GDOCS – FAO

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Small-scale iAVs food production – Integrated fish and plant farming

  1. Introduction to iAVs

Key Features

iAVs: A Solution to the Looming Crisis of Peak Water

The Global Water Crisis

The iAVs Solution

The Way Forward

1.1 HORTICULTURE

1.2 AQUACULTURE

1.3 iAVs

1.4 APPLICABILITY OF iAVs

Added on october 11th

1.5 Goals of iAVs

1.6 CURRENT APPLICATIONS OF AQUAPONICS

1.6.1 Domestic/small-scale aquaponics

1.6.2 Semi-commercial and commercial aquaponics

1.6.3 Education

1.6.4 Humanitarian relief and food security interventions

  1. Understanding iAVs

2.1.1 The nitrogen cycle

Plants are able to use both ammonia and nitrates to perform their growth processes, but nitrates are more easily assimilated by their roots. EXPLAIN MORE….ADD IN AMMONIUM

Nitrifying bacteria, which live in diverse environments such as soil, sand, water and air, are an essential component of the nitrification process that converts plant and animal waste into accessible nutrients for plants. BUT THERE IS ALSO A RANGE OF OTHER SOIL PROCESSES JUST AS, OR EVEN MORE IMPORTANT

This natural process of nitrification by bacteria that happens in soil also takes place in water in the same way. For aquaponics, the animal wastes are the fish excreta released in the culture tanks. The same nitrifying bacteria that live on land will also naturally establish in the water or on every wet surface, converting ammonia from fish waste into the easily assimilated nitrate for plants to use. Nitrification in aquaponic systems provides nutrients for the plants and eliminates ammonia and nitrite which are toxic (Figure 2.5).

2.2 THE BIOFILTER

Formation and Composition

Role in Nutrient Cycling

Algae in the Detritus Layer

Mineralization Process

Maintenance of the Detritus Layer

2.2.3 Depth

Recommended Sand Bed Depth

Considerations for Plant Root Development

Flexibility in Sand Bed Depth

2.3 MAINTAINING A HEALTHY BACTERIAL COLONY

2.3.1 Surface area

GPT-4

2.3.2 Water PH

2.3.3 Water temperature

2.3.4 Dissolved oxygen

2.3.5 Ultraviolet light

2.4 BALANCING THE AQUAPONIC ECOSYSTEM

2.4.1 Nitrate balance

2.4.2 Feed rate ratio

2.4.3 Health check of fish and plants

2.4.4 Nitrogen testing

2.5 CHAPTER SUMMARY

  1. Water quality in aquaponics

3.1 WORKING WITHIN THE TOLERANCE RANGE FOR EACH ORGANISM

3.2 THE FIVE MOST IMPORTANT WATER QUALITY PARAMETERS

3.2.1 Oxygen

3.2.2 PH

Importance of pH

The nitrification process

Fish stocking density

Phytoplankton

3.2.3 Temperature

3.2.4 Total nitrogen: ammonia, nitrite, nitrate

Impacts of high ammonia

Impacts of high nitrite

Impacts of high nitrate

3.2.5 Water hardness

General hardness

Carbonate hardness or alkalinity

Summary of essential points on hardness

3.3 OTHER MAJOR COMPONENTS OF WATER QUALITY: ALGAE AND PARASITES

3.3.1 Photosynthetic activity of algae

3.3.2 Parasites, bacteria and other small organisms living in the water

3.4 SOURCES OF WATER

3.4.1 Rainwater

3.4.2 Cistern or aquifer water

3.4.3 Tap or municipal water

3.4.4 Filtered water

3.5 MANIPULATING PH

3.5.1 Lowering pH with acid

3.5.2 Increasing pH with buffers or bases

3.6 WATER TESTING

3.7 Evaporative Loss Management in iAVs

Transpiration and Biomass Incorporation

Water Exposure and Pumping Regime

Absence of Filters

3.8 CHAPTER SUMMARY

  1. Design of iAVs

4.1 SITE SELECTION

4.1.1 Stability

4.1.2 Exposure to wind, rain and snow

4.1.3 Exposure to sunlight and shade

4.1.4 Utilities, fences and ease of access

4.1.5 Special considerations: rooftop iAVs

4.1.6 Greenhouses and shading net structures

4.2 ESSENTIAL COMPONENTS OF AN AQUAPONIC UNIT

4.2.1 Fish tank

Tank shape

Material

Colour

Covers and shading

Failsafe and redundancy

Mineralization

Using a media bed for a combination of mechanical and biological filtration

4.2.3 Hydroponic components – media beds, NFT, DWC

4.2.4 Water movement

Submersible impeller water pump

Airlift

Human power

4.2.5 Aeration

Sizing aeration systems

Venturi siphons

Cascade Aerators

Cone Aerators

Slat and Coke Aerators

4.2.6 Sump tank

4.2.7 Plumbing materials

4.2.8 Water testing kits

4.3 THE MEDIA BED TECHNIQUE

4.3.1 Water flow dynamics

4.3.2 Biofilter Construction

Materials

Shape

Depth

4.3.3 SAND Choice of medium

Displacement of water by media

4.3.4 Filtration

Mechanical filter

Biological filtration

Mineralization

The Biological Facilitation of Mineralization

The Biofilter and Mineralization

Components of the iAVs System

4.3.5 The three zones of media beds – characteristics and processes

Dry zone

Dry/wet zone

Wet zone

4.3.6 Irrigating media beds

Bell siphon

Timer mechanism

Water flow dynamics

Intermittent Irrigation in iAVs

How Intermittent Irrigation Works

Irrigation Schedule

Nighttime Rest

Pumping Volume

Fine-Tuning and Adaptations

4.4 NUTRIENT FILM TECHNIQUE (NFT)

4.4.1 Water flow dynamics

4.4.2 Mechanical and biological filtration

4.4.3 Nutrient film technique grow pipes, construction and planting

4.5 DEEP WATER CULTURE TECHNIQUE

4.5.1 Water flow dynamics

4.5.2 Mechanical and biological filtration

4.5.3 DWC grow canals, construction and planting

4.5.4 Special case DWC: low fish density, no filters

Low stocking density unit management

Advantages and disadvantages of low stocking density

4.6 COMPARING AQUAPONIC TECHNIQUES

4.7 CHAPTER SUMMARY

  1. Bacteria

5.1 NITRIFYING BACTERIA AND THE BIOFILTER

5.1.1 High surface area

5.1.2 Water pH

5.1.3 Water temperature

5.1.4 Dissolved oxygen

5.1.5 UV light

5.1.6 Monitoring bacterial activity

5.2 HETEROTROPHIC BACTERIA AND MINERALIZATION

5.3 UNWANTED BACTERIA

5.3.1 Sulphate reducing bacteria

5.3.2 Denitrifying bacteria

5.3.3 Pathogenic bacteria

5.4 SYSTEM CYCLING AND STARTING A BIOFILTER COLONY

5.4.1 Adding fish and plants during the cycling process

Inoculating an Integrated AquaVegeculture System

  1. Introducing Fingerlings and Plants
  2. Feeding and Monitoring
  3. Inoculating the System
  4. Alternative Inoculation Methods

5.5 CHAPTER SUMMARY

  1. Plants

6.1 MAJOR DIFFERENCES BETWEEN SOIL AND SOIL-LESS CROP PRODUCTION

6.1.1 Fertilizer

6.1.2 Water use

6.1.3 Utilization of non-arable land

6.1.4 Productivity and yield

6.1.5 Reduced workload

6.1.6 Sustainable monoculture

6.1.7 Increased complication and high initial investment

6.2 BASIC PLANT BIOLOGY

6.2.1 Basic plant anatomy and function

Roots

Stems

Leaves

Flowers

Fruit/seeds

6.2.2 Photosynthesis

6.2.3 Nutrient requirements

Macronutrients

Nitrogen

Phosphorus

Potassium

Calcium

Magnesium

Sulphur

Micronutrients

Iron

Manganese

Boron

Zinc

Copper

Molybdenum

6.2.4 Sources of nutrients

6.3 WATER QUALITY FOR PLANTS

6.3.1 pH

6.3.2 Dissolved oxygen

6.3.3 Temperature and season

6.3.4 Ammonia, nitrite and nitrate

6.4 PLANT SELECTION

6.5 PLANT HEALTH, PEST AND DISEASE CONTROL

6.5.1 Plant pests, integrated production and pest management

Physical, mechanical and cultural controls

Netting/screens

Physical barriers

Hand inspection and removal

Trapping

Environmental management

Plant choice

Indicator plants and sacrificial/catch/trap crops

Companion planting

Fertilization

Spacing

Crop rotation

Sanitation

Chemical controls

Biological controls

Beneficial insects – pest predators

6.5.2 Plant diseases and integrated disease management

Environmental controls

Plant choice

Plant nutrition

Monitoring – inspection and exclusion

Treatment – inorganic or chemical

Treatment – biological

6.6 PLANTING DESIGN

Encouraging plant diversity

Staggered planting

Maximizing space in media beds

6.7 CHAPTER SUMMARY

  1. Fish in aquaponics

7.1 FISH ANATOMY, PHYSIOLOGY AND REPRODUCTION

7.1.1 Fish anatomy

Main external anatomical features

Eyes

Scales

Mouth and jaws

Gill cover/operculum

Vent

Fins

Respiration

Excretion

7.1.2 Fish reproduction and life cycle

7.2 FISH FEED AND NUTRITION

7.2.1 Components and nutrition of fish feed

7.2.2 Pelletized fish feed

Avoid overfeeding

7.2.3 Feed conversion ratio for fish and feeding rate

7.2.4 Integrated AquaVegeculture System (iAVs): Feed and Ratio Guidelines

Feed Rates

Water-to-Sand Ratio

Fish Density

Observations and Adjustments

7.2.5 iAVs Feeding and Pump Schedule

Feeding Times

Pump Cycles

7.3 WATER QUALITY FOR FISH

7.3.1 Nitrogen

7.3.2 pH

7.3.3 Dissolved oxygen

7.3.4 Temperature

7.3.5 Light and darkness

7.4 FISH SELECTION

7.4.1 Tilapia

Main commercial types:

Description

Nile Tilapia: A Resilient and Nutritious Choice for Integrated AquaVegeculture Systems

Resilience and Growth

Nutritional Benefits

Contribution to Plant Growth

Legal Considerations and Recommendations

7.4.2 Carp

Main commercial types:

Description

Other carp species (ornamental fish)

7.4.3 Catfish

Main commercial types:

Description

7.4.4 Trout

Main commercial type:

Description

7.4.5 Largemouth bass

Main commercial type:

Description

7.4.6 Prawns

7.5 ACCLIMATIZING FISH

7.6 FISH HEALTH AND DISEASE

7.6.1 Fish health and well-being

7.6.2 Stress

7.6.3 Fish disease

Preventing disease

Recognizing disease

External signs of disease:

Behavioural signs of disease:

Abiotic diseases

Biotic diseases

Treating disease I

Salt bath treatment

7.7  Fish Harvesting in iAVs

Harvesting Stages

7.8 PRODUCT QUALITY

7.9 CHAPTER SUMMARY

  1. Management and troubleshooting

8.1 COMPONENT CALCULATIONS AND RATIOS

8.1.1 Plant growing area, amount of fish feed and amount of fish

8.1.2 Water volume

8.1.3 Filtration requirements – biofilter and mechanical separator

8.1.4  Sand Testing

Performing the Differential Settling Test and Determining Soil Composition

8.1.5 Understanding Pore Space Volume in iAVs

Role of Pore Space Volume

Measuring Pore Space Volume

Impact of Pore Space Volume

Changes in Pore Space Volume

8.1.6 Sand Hydraulic Conductivity in iAVs

Importance of Hydraulic Conductivity

Flood and Drain Cycle

Oxygen Supply

Measuring Hydraulic Conductivity

Sand Selection

8.1.7 Moisture Management in Integrated AquaVegeculture Systems (iAVs)

Understanding Water Retention

Role of Biofilm in Water Retention

Pore Space and Hydrostatic Tension

Water Retention Variations

Testing Water Retention

8.2 NEW AQUAPONIC SYSTEMS AND INITIAL MANAGEMENT

8.2.1 Building and preparing the unit

Media bed unit preparation

8.2.2 System cycling and establishing the biofilter

8.3 MANAGEMENT PRACTICES FOR PLANTS

8.3.1 Review of planting guidelines

Plant selection

Plant spacing

Supplementing iron

8.3.2 Establishing a plant nursery

Direct seeding in media beds

8.3.3 Transplanting seedlings

Media bed planting

8.3.4 Harvesting plants

Staggered planting and harvesting

Harvesting approaches

8.3.5 Managing plants in mature systems

Stabilizing pH

Organic fertilizers

Pests and disease

Follow seasonal planting advice

8.3.6 Plants – summary

8.4 MANAGEMENT PRACTICES FOR FISH

8.4.1 Fish feeding and growth rates

8.4.2 Harvesting and staggered stocking

8.4.3 Fish – summary

8.5 ROUTINE MANAGEMENT PRACTICES

8.5.1 Daily activities

8.5.2 Weekly activities

8.5.3 Monthly activities

8.6 SAFETY AT WORK

8.6.1 Electrical safety

8.6.2 Food safety

8.6.3 General safety

8.6.4 Safety – summary

8.7 TROUBLESHOOTING

8.8 Backup & Protection

8.8.1 Backup and Protection in iAVs Systems

8.9 CHAPTER SUMMARY

  1. Additional topics on aquaponics

9.1 SUSTAINABLE, LOCAL ALTERNATIVES FOR AQUAPONIC INPUTS

9.1.1 Organic plant fertilizers

General composting process

Compost tea and secondary mineralization

Other nutrient teas

Compost safety

9.1.2 Alternative fish feed

Duckweed

Azolla, a water fern

Insects

Black soldier flies

Moringa or kalamungay

9.1.3 Seed collection

Dry seed pods

Wet seed pods

Seed storage

9.1.4 Rainwater harvesting

9.1.5 Alternative building techniques for aquaponic units

9.1.6 Alternative energy for aquaponic units

Photovoltaic electricity

Insulation

Spiral heating

9.2 SECURING WATER LEVELS FOR A SMALL-SCALE UNIT

9.2.1 Float switches

9.2.2 Overflow pipes

9.2.3 Standpipes

9.2.4 Animal fences

9.3 INTEGRATING AQUAPONICS WITH OTHER GARDENS

9.3.1 Irrigation and fertilization

9.3.2 Irrigating wicking beds

9.4 EXAMPLES OF SMALL-SCALE AQUAPONIC SETUPS

9.4.1 Aquaponics for livelihood in Myanmar

9.4.2 Saline aquaponics

9.4.3 Bumina and Yumina

9.5 CHAPTER SUMMARY

10 – Business / Commercial Aspects

10.1 Investigating the Profitability of Integrated AquaVegeculture Systems

10.2 Commercialization of iAVs

Production and Marketing: Two Sides of the Same Coin

The Art of Pre-Selling

The Importance of Understanding the Market

10.3 Commercialization Challenges in iAVs

Understanding the Novice’s Journey

The Risk of Over-Optimism

The Importance of Collaboration

The Role of Experience

11 – Case Studies

11.1 Gordon Watkins

The Beginning

The Greenhouse

The iAVs

The Plants and Fish

Balancing the System

26 Years Later

11.1.2 Boone Mora

Further reading

Recirculating aquaculture and fish breeding

Species profiles

Aquaponics

Bacteria, microbes and the nitrogen cycle

Bell siphon design and construction

Fish feeds

Compost tea

Fish diseases

Greenhouses and net houses

Nutrient deficiencies

Plant diseases

Pest management

Soil-less culture

Wicking beds

Glossary

Appendix 1 – Vegetable production guidelines for 12 common aquaponic plants

BASIL

Growing basil in aquaponic units:

Growing conditions:

Growing instructions:

Harvesting:

CAULIFLOWER

Growing cauliflower in aquaponic units:

Growing conditions:

Growing instructions:

Harvesting:

LETTUCE (MIXED SALAD LEAVES):

Growing lettuce in aquaponic units:

Growing conditions:

Growing instructions:

Harvesting:

CUCUMBERS

Growing cucumbers in aquaponic units:

Growing conditions:

Growing instructions:

Harvesting:

EGGPLANT

Growing eggplant in aquaponic units:

Growing conditions:

Growing instructions:

Harvesting:

PEPPERS

Growing peppers in aquaponic units:

Growing conditions:

Growing instructions:

Harvesting:

TOMATO

Growing tomatoes in aquaponic units:

Growing conditions:

Planting instructions:

Harvesting:

BEANS AND PEAS

Growing beans in aquaponic units:

Growing conditions for pole beans:

Growing instructions for pole beans:

Harvesting:

Snap bean varieties (green or yellow wax beans) –

Shell beans (black, broad or fava beans) –

Dried beans (kidney beans and soybeans) –

HEAD CABBAGE

Growing cabbage in aquaponic units:

Growing conditions:

Growing instructions:

Harvesting:

BROCCOLI

Growing broccoli in aquaponic units:

Growing conditions:

Growing instructions:

Harvesting:

SWISS CHARD / MANGOLD

Growing Swiss chard in aquaponic units:

Growing conditions:

Growing instructions:

Harvesting:

PARSLEY

Growing parsley in aquaponic units:

Growing conditions:

Growing instructions:

Harvesting:

Appendix 2 – Plant pests and disease control

PEST CONTROL: REPELLENTS, SOFT-CHEMICALS AND PLANT-DERIVED INSECTICIDES

PEST CONTROL: INSECTICIDES, PLANT-DERIVED

PEST CONTROL: BENEFICIAL INSECTS

DISEASE CONTROL: ENVIRONMENTAL

DISEASE CONTROL: INORGANIC CHEMICAL

COMPANION PLANTING CHART

Appendix 3 – Fish pests and disease control

Appendix 4 – Calculating the amount of ammonia and biofilter media for an aquaponic unit

DETERMINING THE AMOUNT OF AMMONIA PRODUCED BY FEED

DETERMINING THE AMOUNT OF BIOFILTER MEDIA NEEDED BY NITRIFYING BACTERIA

Appendix 5 – Making homemade fish feed

COMPOSITION OF FEED

Proteins

Carbohydrates

Lipids

Energy

Vitamins and minerals

ON-FARM FEED PRODUCTION

TABLE SKIPPED

HOMEMADE FISH FEED FORMULATIONS FOR OMNIVOROUS/HERBIVOROUS FISH

Step-by-step preparation of homemade fish feed

TABLE SKIPPED

STORING HOMEMADE FEED

SUPPLEMENTARY FEEDING WITH LIVE FEEDS

Appendix 6 – Key considerations before setting up an iAVs

ECONOMIC FACTORS

ENVIRONMENTAL FACTORS

LOGISTICAL AND MANAGERIAL FACTORS

SOCIAL CONDITIONS

SUMMARY OF ESSENTIAL REQUIREMENTS FOR iAVs AT DIFFERENT SCALES

Appendix 7 – Cost-benefit analysis for small-scale iAVs

CALCULATION ASSUMPTIONS

Important:

Appendix 8 – Step-by-step guide to constructing small-scale aquaponic systems

INITIAL COMMENTS ON THE THREE SYSTEM DESIGNS

SECTION 1 – THE MEDIA BED UNIT

  1. PREPARING THE FISH TANK

SECTION 2 – Building the iAVs in Developing Nations

DSC03874

SECTION 3 – THE DEEP WATER CULTURE (DWC) UNIT

APPENDIX 9

Commercial Production

Production

Marketing

The Interplay of Production and Marketing

The Role of Experience and Enthusiasm

The Importance of Understanding Strengths and Weaknesses

Aquaponics quick-reference handout

INTRODUCTION TO AQUAPONICS

BENEFITS AND WEAKNESSES OF AQUAPONIC FOOD PRODUCTION

Major benefits of aquaponic food production:

Major weaknesses of aquaponic food production:

TECHNICAL INTRODUCTION

WATER QUALITY IN AQUAPONICS

AQUAPONIC UNIT DESIGN

BACTERIA IN AQUAPONICS

PLANTS IN AQUAPONICS

FISH IN AQUAPONICS

BALANCING THE FISH AND PLANTS: COMPONENT CALCULATIONS

ADDITIONAL TOPICS IN AQUAPONICS

TEN KEY GUIDELINES FOR SUCCESSFUL AQUAPONICS

 

Small-scale iAVs food production – Integrated fish and plant farming

NEED TO DO A PASS OVER AND CONSIDER REMOVING ANYTHING THAT COMPLICATES THINGS FOR NO GOOD REASON – PERHAPS LIST THEM AT THE END FOR ARCHIVAL REASONS OR FOR LATER EDITING/INCLUSION – OR FOR OTHER USES?

1. Introduction to iAVs

The Integrated AquaVegeculture System (iAVS) is a sustainable and efficient closed-loop aquaculture system that utilizes sand as a substrate for plant growth. This innovative method of agriculture is designed to maximize resource use while combining horticulture and aquaculture practices.

Key Features

  • Closed-loop System: iAVS recirculates water and nutrients within the system, reducing waste and conserving resources.
  • Sand Substrate: The use of sand as a substrate for plant growth provides a natural, soil-like environment that supports healthy plant development.
  • Resource Efficiency: By integrating aquaculture and horticulture, iAVs maximizes the use of resources such as water, nutrients, and energy.
  • Sustainability: iAVs promotes sustainable agriculture practices by minimizing waste and reducing the environmental impact of traditional farming methods.

TITLE OR REWRITE AND REORGANIZE SECTION

 

This chapter provides a full description of the concept of iAVs, a technique for combining horticulture and aquaculture in a system that cultivates plants in recirculated aquaculture water. 

 

iAVs is described, including additional considerations and a brief history of its development. An account of the strengths of iAVs food production is provided, as well as the places and contexts where iAVs is most, and least, appropriate. Finally, there is a short description of the major applications of iAVs seen today

New version

This chapter offers a comprehensive overview of iAVs, a method that merges horticulture and aquaculture in a system that grows plants in recirculated aquaculture water. The chapter covers the following topics:

  • A description of iAVs, including additional considerations and a brief history of its development
  • An analysis of the strengths of iAVs
  • The most and least appropriate places and contexts for implementing iAVs

Added october 11th

The consistent production of high-quality, substantial food is crucial for individual, cultural, and national survival. For true development, human populations need high-quality proteins, vitamins, and minerals for proper nutrition. Fish and vegetables are excellent sources of these nutrients. Hence, there is a pressing need to establish a technology that enables efficient cultivation of these food groups while preserving freshwater and land resources.

The aim of the [iAVs] technology described here is to aid people in arid and semi-arid regions in their efforts to enhance food security and establish a year-round production capability to cater to the needs of a rapidly growing population. Higher annual growth rates in the agricultural sector will result in increased agricultural incomes and capital formation on farms. Moreover, such changes will have a multiplying effect on rural and industrial employment.

Given that the iAVs technology is highly conservative of indigenous natural resources, particularly fresh water supplies, it is considered most suitable for: application in regions with insufficient rainfall or other water resources, areas with soils unsuitable for traditional agricultural practices, and locales with burgeoning or unsustainable population levels.

The integrated aquaculture approach, specifically the Integrated AquaVegeculture System (iAVs), offers several significant advantages:

  1. Water Conservation: This system allows for the utilization of a given water volume from 120 to 300 times, compared to the 1 to 3 times typically associated with other recirculating systems. This results in a substantial increase in fish yield per unit volume of water consumed, along with the production of vegetable crops.
  2. Waste Utilization: The “waste” products from aquaculture are used to produce food and reduce pollution, creating a more sustainable and efficient system.
  3. Intensive Production: iAVs allows for the intensive production of both fish protein and vegetable crops, maximizing the output from a given area.
  4. Reduced Operating Costs: By integrating aquaculture and olericulture (vegetable farming), the operating costs are lower than if each production system was run separately.
  5. Unrestricted by Environmental Constraints: The use of recirculating systems is not limited by water supply, soil type, or land availability, unlike pond or cage aquaculture. For instance, water consumption in recirculatory integrated systems which culture tilapia is less than 1% of that required in pond culture techniques to produce equivalent yields.

This co-production system is particularly beneficial for arid or semi-arid regions where there is high demand for fish and fresh vegetables, and where water and/or land resources are limited. Each liter of water used in this system can produce 0.7 grams of protein and 7 kilo-calories of food-energy in fish and fruit, along with most essential vitamins. This level of production is at least several orders of magnitude (1,000+ times) more efficient in the use of water than open-field production in the U.S., such as poultry and corn. Therefore, iAVs is a significant innovation in aquaculture practices, especially for regions where water and/or land is limiting to food production.

iAVs: A Solution to the Looming Crisis of Peak Water

The term “peak oil” is familiar to many, referring to the hypothetical point when global oil production reaches its zenith before gradually declining. However, a less familiar but equally critical concept is “peak water” – the point at which freshwater availability reaches its maximum before a steady decline sets in.

In the face of this looming crisis, the Integrated AquaVegeculture System (iAVs) offers a promising solution. This innovative system combines horticulture and aquaculture in a fully organic growing method, using less than 1% of the water per fish biomass production compared to traditional pond culture of tilapia. 

Additionally, the vegetable crops grown in this system require less than 10% of the water compared to traditional field culture, making iAVs a highly water-efficient method of food production.

The Global Water Crisis

The reality of peak water is already being felt in many parts of the world. In Africa, 65% of the arable land is unable to sustain food production due to water scarcity and land degradation(1).  Meanwhile, China, home to the world’s largest population, is grappling with severe water contamination issues. Reports indicate that 75% of China’s rivers and lakes and 50% of its groundwater are contaminated, rendering them unsuitable for agriculture, livestock, or human consumption(3).

The iAVs Solution

The inherent water-use efficiencies of the Integrated AquaVegeculture System (iAVs) could have a profound effect, particularly in regions where water scarcity is a pressing issue. 

For example, in Egypt, implementing iAVs could drastically decrease the resources needed for tomato cultivation. The land area required could be reduced by over 94%, and the water requirement could be cut by more than 92%(1). Additionally, this system allows for the production of fish without any additional water demand, essentially providing a ‘free’ source of protein(3).

This is particularly significant in the context of Egypt’s agricultural sector, which is under increasing pressure to reduce water use, increase crop productivity, and lower production costs due to escalating water pressures(2). The country’s aquaculture industry has seen rapid development over the past seven years, becoming a key contributor to Egypt’s food security and economy(3). However, water scarcity remains a significant challenge(3).

The dual use of water for fish and crop production, as seen in iAVs, could be a promising approach to improve irrigation under arid conditions1. This aligns with Egypt’s nationwide strategy to encourage the use of modern irrigation methods and technologies to save water and reduce production costs(2).

iAVs works by recycling each liter of water between 150 to 300 times before it is ‘lost’ or incorporated into biomass. This high rate of water recycling, combined with the system’s ability to produce both fish and vegetables, makes iAVs a highly sustainable solution to the challenges of peak water.

The Way Forward

 

As the world grapples with the realities of peak water, innovative solutions like iAVs offer a beacon of hope. By adopting such water-efficient methods of food production, countries can not only ensure food security for their populations but also contribute to global efforts to conserve our planet’s precious water resources.

iAVs system provided a sustainable solution to the global water crisis.

 

1.1 HORTICULTURE

MAY NEED A TOTAL REWRITE SO IT PROPERLY MATCHES THE SECTION TITLE

Soil-based culture is the method of growing agricultural crops with the use of soil. To make soil, an inert growing media, also called substrate, is used. This media provide plant support and moisture retention. Irrigation systems are integrated within these media, thereby introducing a nutrient solution to the plants’ root zones. This solution provides all the necessary nutrients for plant growth. 

 

New version

The Integrated AquaVegeculture System (iAVs), employs a unique method of cultivating agricultural crops using sand as the primary medium. The sand serves a dual purpose: it offers structural support to the plants and creates pore space. Incorporated within this medium are furrow irrigation systems, which deliver a nutrient-rich solution directly to the root zones of the plants. This nutrient solution is comprehensive, supplying all the essential elements required for optimal plant growth. THIS IS CRAP

 

Sand can be reused indefinitely, which meets the particular demands of intensive production. Farmers have also improved plant performance through increased control over several crucial factors of plant growth. Nutrient availability at plant roots is better manipulated, monitored and real-time controlled, leading to higher quantitative and qualitative productions. 

 

Beyond its significantly higher yields compared with traditional agriculture, iAVs is important because of its higher water- and fertilizer-use efficiency, which makes iAVs the most suitable farming technique in arid regions or wherever nutrient dispersal is an issue for both environmental and economic reasons. Paraphrased into new comment below

 

iAVs stands out as a crucial farming technique due to its superior water efficiency and significantly higher yields compared to traditional agriculture. This makes iAVs particularly suitable for arid regions.

 

iAVs is a significant advancement in agricultural practices for several reasons:

  1. Higher Yields:

 iAVs has been shown to produce significantly higher yields compared to traditional agriculture. This increase in productivity makes it a promising solution for meeting the growing global demand for food.

  1. Water and Fertilizer Efficiency:

 iAVs is highly efficient in its use of water and fertilizer. The system recycles water and uses fish effluents as crop fertilizers, which not only increases productivity but also contributes to its sustainability.

  1. Suitability for Arid Regions: 

Due to its efficient use of water and nutrients, iAVs is particularly suitable for farming in arid regions. These areas often face challenges in traditional agriculture due to water scarcity and poor soil quality. iAVs, with its ability to utilize sand as a growing medium, provides a viable solution for these regions.

  1. Environmental and Economic Benefits: 

iAVs addresses the issue of nutrient dispersal, which is a significant concern for both environmental and economic reasons. In traditional agriculture, excess nutrients from fertilizers can lead to environmental issues such as eutrophication of water bodies and harmful algal blooms(5). By efficiently utilizing nutrients, iAVs can help mitigate these environmental impacts. Economically, the efficient use of resources in iAVs can lead to cost savings in terms of reduced need for water and fertilizers.

 

iAVs can instead be developed in arid lands, in saline-prone areas, as well as in urban and suburban environments or wherever the competition for land and water or unfavourable climatic conditions require the adoption of intensive production systems. The high productivity for the small space required makes iAVs an interesting method for food security or for the development of micro-scale farming with zero food miles. Paraphrased into new comment below

 

iAVs is a versatile farming method designed for arid regions, saline-prone areas, and urban or suburban environments, or in situations where land and water competition or unfavorable climatic conditions necessitate the use of intensive production systems. 

Due to its high productivity in a small space, iAVs is an appealing approach for enhancing food security and promoting micro-scale farming with zero food miles.

 

To summarize, the four main reasons why iAVs is an expanding agricultural practice are: decreased presence of soil-borne diseases and pathogens because of sterile conditions; improved growing conditions that can be manipulated to meet optimal plant requirements leading to increased yields; increased water- and fertilizer-use efficiency; and the possibility to develop agriculture where suitable land is not available. In addition with the rising in demand for chemical- and pesticide-free produce and more sustainable agricultural practices, there has been extensive research into organic methods. Section 6.1 discusses these differences in more detail. A major concern regarding the sustainability of modern agriculture is the complete reliance on manufactured, chemical fertilizers to produce food. Paraphrased below

 

In summary, iAVs is gaining traction for several key reasons:

 

It offers enhanced growing conditions that can be tailored to meet optimal plant requirements, leading to increased yields; it boasts greater efficiency in water and fertilizer use; and it enables agricultural development in areas where suitable land is scarce. 

 

As the demand for chemical- and pesticide-free produce and sustainable agricultural practices continues to rise, iAVs presents a promising solution for addressing these needs.

Paragraphs dont flow cohesively?

These nutrients can be expensive and hard to source, and often come from environmentally harsh practices accounting for a substantial contribution of all carbon dioxide (CO2) emissions from agriculture. The supply of many of these crucial nutrients is being depleted at a rapid pace, with projections of global shortages within the next few decades. 

 

However, it does not require fuel to plough soil, it does not require additional energy to pump much higher volumes of water for irrigation or to carry out weeding control, and it does not disrupt soil organic matter through intensive agricultural practices. The initial costs, building materials, and reliance on electricity and inputs will also be important limitations to iAVs, but in this case the need for chemical fertilizers is completely removed.

 

1.2 AQUACULTURE

Aquaculture is the captive rearing and production of fish and other aquatic animal and plant species under controlled conditions. Many aquatic species have been cultured, especially fish, crustaceans and molluscs and aquatic plants and algae. Aquaculture production methods have been developed in various regions of the world, and have thus been adapted to the specific environmental and climatic conditions in those regions. Paraphrased below – too long?

 

Aquaculture refers to the controlled cultivation of aquatic species, including fish, crustaceans, mollusks, and aquatic plants, in various water environments. This practice has been adapted to suit the unique environmental and climatic conditions of different regions around the world. Key reasons for the growing popularity of aquaculture include its ability to provide enhanced growing conditions for optimal plant requirements, leading to increased yields; its efficient use of water and fertilizer; and the potential for agricultural development in areas where suitable land is unavailable. As the demand for chemical- and pesticide-free produce and sustainable agricultural practices continues to rise, aquaculture offers a promising solution for addressing these needs.

 

The four major categories of aquaculture include open water systems (e.g. cages, longlines), pond culture, flow-through raceways and recirculating aquaculture systems (RAS). paraphrased The four primary categories of aquaculture encompass open water systems (such as cages and longlines), pond culture, flow-through raceways, and recirculating aquaculture systems (RAS). 

 

In a RAS operation, water is reused for the fish after a cleaning and a filtering process. Although a RAS is not the cheapest production system owing to its higher investment, energy and management costs, it can considerably increase productivity per unit of land and is the most efficient water-saving technology in fish farming. A RAS is the most applicable method for the development of integrated aquaculture agriculture systems because of the possible use of by-products and the higher water nutrient concentrations for vegetable crop production.

 

iAVs has been developed from the beneficial buildup of nutrients occurring in RAS’s and, therefore, is the prime focus of this manual. 

 

Aquaculture is an increasingly important source of global protein production. In fact, aquaculture accounts for almost one-half of the fish eaten in the world, with aquaculture production matching capture fisheries landings for the first time in 2012. 

 

Aquaculture has the potential to decrease the pressure on the world’s fisheries and to significantly reduce the footprint of less-sustainable terrestrial animal farming systems in supplying humans with animal protein. 

 

However, two aspects of aquaculture may be addressed to improve the sustainability of this agricultural technique. One major problem for the sustainability of aquaculture is the treatment of nutrient-rich wastewater, which is a by-product of all the aquaculture methods mentioned above. Depending on the environmental regulations set by each country, farmers must either treat or dispose of the effluent, which can be both expensive and environmentally harmful. 

 

Without treatment, the release of nutrient-rich water can lead to eutrophication and hypoxia in the watershed and localized coastal areas, as well as macroalgae overgrowth of coral reefs and other ecological and economical disturbances. 

 

Growing plants within the effluent stream is one method of preventing its release into the environment and of obtaining additional economic benefits from crops growing with costless by-products through irrigation, artificial wetlands, and other techniques. Another sustainability concern is that aquaculture relies heavily on fishmeal as the primary fish feed. From a conservation standpoint, this is discharging one debt by incurring another, and alternative feed ingredients are an important consideration for the future of aquaculture. 

 

The majority of this publication is dedicated to reusing aquaculture effluent as a value added product, while alternative fish feeds and their ways to contribute to reducing the aquaculture footprint are discussed in Section 9.1.2.

 

1.3 iAVs

iAVs is the integration of recirculating aquaculture and horticulture in one production system.

 

In an iAVs, water from the fish tank cycles through plant grow beds, referred to as a biofilter, and then back to the fish. In the grow bed (biofilter), the fish waste is removed from the water,

 

The biofilter provides a location for bacteria to convert ammonia, which is toxic for fish, into nitrate and ammonium, more accessible nutrients for plants. ADD A SECTION ABOUT SOIL BIOLOGY, AND ALSO HOW ALGAE IS A NUTRIENT SINK, AND ALSO HOW PH ALLOWS FOR A CHEMICAL REACTION WHEREBY AMMONIA IS CONVERTED TO AMMONIUM.  This process is called nitrification. 

 

As the water (containing nitrate and other nutrients) travels through the biofilter, the plants uptake these nutrients, and finally the water returns to the fish tank, purified. 

 

This process allows the fish, plants, and bacteria to thrive symbiotically and to work together to create a healthy growing environment for each other, provided that the system is properly balanced.

 

In iAVs, the aquaculture effluent is diverted through plant beds and not released to the environment, while at the same time the nutrients for the plants are supplied from a sustainable, cost-effective and non-chemical source. This integration removes some of the unsustainable factors of running aquaculture and horticulture systems independently. 

 

Beyond the benefits derived by this integration, iAVs has shown that its plant and fish productions are comparable with, not only hydroponics and recirculating aquaculture systems, but also land-based agriculture.

 

iAVs has been proven to be more productive and economically feasible in certain situations, especially where land and water are limited. 

However, aquaponics is complicated and requires substantial start-up costs. The increased production must compensate for the higher investment costs needed to integrate the two systems.

 

Before committing to a large or expensive system, a full business plan considering economic, environmental, social and logistical aspects should be conducted. 

 

Although the production of vegetables and fruit is the most visible output of iAVs, it is essential to understand that iAVs is the management of a complete ecosystem that includes three major groups of organisms: fish, plants and bacteria, with bacteria being the most important.

 

1.4 APPLICABILITY OF iAVs

iAVs combines two of the most productive systems in their respective fields. Recirculating aquaculture systems and horticulture have experienced widespread expansion in the world not only for their higher yields, but also for their better use of land and water, simpler methods of pollution control, improved management of productive factors, their higher quality of products and greater food safety. 

 

Environmentally, iAVs prevents aquaculture effluent from escaping and polluting the watershed. 

 

iAVs enables greater water and production control.  iAVsdoes not rely on chemicals for fertilizer, or control of pests or weeds, which makes food safer against potential residues. 

 

Socially, iAVs can offer quality-of-life improvements because the food is grown locally, and culturally appropriate crops can be grown. 

 

iAVs can integrate livelihood strategies to secure food and small incomes for landless and poor households. Domestic production of food, access to markets and the acquisition of skills are invaluable tools for securing the empowerment and emancipation of women in developing countries, and iAVs can provide the foundation for fair and sustainable socio-economic growth. 

 

Fish protein is a valuable addition to the dietary needs of many people, as protein is often lacking in small-scale gardening. 

 

iAVs is most appropriate where land is expensive, water is scarce, and soil is poor. 

 

Deserts and arid areas, sandy islands and urban gardens are the locations most appropriate for  iAVs because it uses an absolute minimum of water.  iAVs avoids the issues associated with soil compaction, salinization, pollution, disease and tiredness. 

 

Similarly, iAVs can be used in urban and peri-urban environments where no or very little land is available, providing a means to grow dense crops on small balconies, patios, indoors or on rooftops.

 

iAVs is quite adaptable and can be developed with local materials and domestic knowledge, and to suit local cultural and environmental conditions. It will always require a dedicated and interested person, or group of persons, to maintain and manage the system on a daily basis. 

 

Success is derived from the local, sustainable and intensive production of both fish and plants and, possibly, these could be higher than the two components taken separately, so long as iAVs is used in appropriate locations while considering its limitations.

 

Added on october 11th

The first application of iAVs is on a small scale, specifically tailored for small-holder activities. This approach utilizes local inputs, making it an ideal solution for communities aiming for food self-sufficiency. By leveraging local resources, small-holder iAVs can produce enough food to sustain the community, with surplus produce available for sale in the cash market. 

 

This not only ensures food security but also provides an additional income stream for the community, contributing to economic stability and growth.

 

The second application of iAVs is on a larger scale, designed for commercial enterprises located near population centers. These large-scale operations can produce significant quantities of food, meeting the demands of a larger population and potentially contributing to regional or even national food supply chains. 

 

This approach can be particularly beneficial in urban or peri-urban areas, where traditional farming methods may be impractical due to space constraints.

 

Regardless of the scale, iAVs can be seamlessly integrated with existing or planned water harvesting, gardening, or greenhouse projects. This flexibility allows for the optimization of resources and space, further enhancing the efficiency and sustainability of food production.

 

The versatility of iAVs makes it particularly suitable for regions where water and land resources are limiting factors in food production. By efficiently using water and land, iAVs can help overcome these challenges, enabling sustainable and productive food production even in the most resource-constrained environments.

 

1.5 A BRIEF HISTORY OF MODERN AQUAPONIC TECHNOLOGY

 

The concept of using faecal waste and overall excrement from fish to fertilize plants has existed for millennia, with early civilizations in both Asia and South America applying this method. 

 

Through the pioneering work of the New Alchemy Institute and other North American and European academic institutions in the late 1970s, and further research in the following decades, this basic form of aquaculture evolved into the modern food production systems of today. 

 

Prior to the technological advances of the 1980s, most attempts to integrate hydroponics and aquaculture had limited success. 

 

The 1980s and 1990s saw advances in system design, biofiltration and the identification of the optimal fish-to-plant ratios that led to the creation of closed systems that allow for the recycling of water and nutrient buildup for plant growth. 

 

In its early systems, North Carolina State University (United States of America) demonstrated that water consumption in integrated systems was just 5 percent of that used in pond culture for growing tilapia. This development, among other key initiatives, pointed to the suitability of integrated aquaculture and horticulture for raising fish and growing vegetables, particularly in arid and water poor regions. 

 

Although in use since the 1980s, iAVs is still a relatively new method of food production, with only a small number of research and practitioner hubs worldwide with comprehensive experience. 

 

1.5 Goals of iAVs

 

The goal of iAVs is to assist the peoples of the arid and semiarid regions in their endeavors to increase food security and establish a year-round production capability to meet the demands of a rapidly increasing population. 

Increased annual growth rates in the agricultural sector will produce increases in agricultural incomes and on-farm capital formation. In addition, such changes will produce multiplying effects on rural and industrial employment.

Because iAVs is extremely conservative of the indigenous natural resources, especially of fresh water supplies, it is deemed most appropriate for: application in the regions with inadequate rainfall or other water-resources, areas with soils unsuitable for the practice of traditional agriculture methodologies, and locals with burgeoning or unsustainable levels of population.”

 

1.6 CURRENT APPLICATIONS OF iAVs

 

This final section briefly discusses some of the major applications of iAVs seen around the world. This list is by no means exhaustive, but rather a small window into activities that are using the iAVs concept. WHERE IS THE LIST?!

 

Appendix 6 includes further explanation as to where and in what contexts iAVs is most applicable.

 

1.6.1 Domestic/small-scale 

iAVs units with a fish tank size of about 500 -1000  liters are considered small-scale, and are appropriate for domestic production for a family household. 

 

Units of this size have been trialed and tested with great success in many regions around the world. The main purpose of these units is food production for subsistence and domestic use, as many units can have various types of vegetables, herbs as well as fruit growing at once. 

 

1.6.2 Semi-commercial and commercial iAVs

 

Detailed business plans with thorough market research on the most lucrative plants and fish in local and regional markets are essential for any successful venture, 

 

ADD LINK TO COMMERCIAL SECTION? OR REMOVE THIS BIT?

 

1.6.3 Education

Small-scale aquaponic units are being championed in various educational institutes including, primary and secondary schools, colleges and universities, special and adult education centres, as well as community-based organizations (Figure 1.8). Aquaponics is being used as a vehicle to bridge the gap between the general population and sustainable agricultural techniques, including congruent sustainable activities such as rainwater harvesting, nutrient recycling and organic food production, which can be integrated within the lesson plans. Moreover, this integrated nature of aquaponics provides hands-on learning experience of wide-ranging topics such as anatomy and physiology, biology and botany, physics and chemistry, as well as ethics, cooking, and general sustainability studies.

 

1.6.4 Humanitarian relief and food security interventions

With the advent of highly efficient aquaponic systems, there has been an interest in discovering how the concept fares in developing countries. Examples of aquaponic initiatives can be seen in Barbados, Brazil, Botswana, Ethiopia, Ghana, Guatemala, Haiti, India, Jamaica, Malaysia, Mexico, Nigeria, Panama, the Philippines, Thailand and Zimbabwe (Figure 1.9). At first glance, there appears to be a considerable amount of aquaponic activity within the humanitarian sphere. In addition, small-scale aquaponic units are components of some urban or peri-urban agriculture initiatives, particularly with non-governments organizations and other stakeholders in urban food and nutrition security, because of their ability to be installed in many different urban landscapes. In particular, the Food and Agriculture Organization of the United Nations (FAO) has piloted small-scale aquaponic units on rooftops in The West Bank and Gaza Strip – in response to the chronic food and nutrition security issues seen across the region (Figure 1.10). To date, this pilot project and subsequent scale-up are one of a growing number of examples around the world where aquaponics is being successfully integrated into medium-scale emergency food security interventions. However, many attempts are ad hoc and opportunistic, in many cases leading to stand-alone, low-impact interventions, so caution should be used when evaluating the success of humanitarian aquaponics. In the recent years there has been a surge of aquaponic conferences worldwide. Furthermore, aquaponics is increasingly a part of conferences on aquaculture and hydroponics. Many of these panels outline the raising concerns among researchers from different backgrounds and specializations, policy makers and stakeholders to find sustainable solutions to ensure a long-lasting growth and secure increased food output for a growing world population.

 

2. Understanding iAVs

Building from the initial explanation of iAVs in Chapter 1 NEED TO CHECK, this chapter discusses the biological processes occurring within an iAVs. 

 

First, the chapter explains the major concepts and processes involved, including the nitrification process. It then examines the vital role of bacteria and their key biological processes. 

 

Finally, there is a discussion of the importance of balancing the ecosystem consisting of the fish, plants and bacteria, including how this can be achieved while maintaining an iAVs over time. 

 

2.1 IMPORTANT BIOLOGICAL COMPONENTS OF AQUAPONICS

 

As described in Chapter 1, iAVs is a form of integrated agriculture that combines two major techniques, aquaculture and horticulture. In one continuously recirculating unit, culture water exits the fish tank containing the metabolic wastes of fish. The water first passes through a biofilter that captures solid waste and also oxidizes ammonia to nitrate. 

 

The water then returns purified, to the fish tank. The biofilter provides a habitat for bacteria to convert fish waste into accessible nutrients for plants. 

 

These nutrients, which are dissolved in the water, are then absorbed by the plants. 

 

This process of nutrient removal cleans the water, preventing the water from becoming toxic with harmful forms of nitrogen (ammonia and nitrite), and allows the fish, plants, and bacteria to thrive symbiotically. 

 

Thus, all the organisms work together to create a healthy growing environment for one another, provided that the system is properly balanced.

 

2.1.1 The nitrogen cycle 

The most important biological process in aquaponics is the nitrification process, which is an essential component of the overall nitrogen cycle seen in nature. 

 

Nitrogen (N) is a chemical element and an essential building block for all life forms. It is present in all amino acids, which make up all proteins which are essential for many key biological processes for animals such as enzyme regulation, cell signalling and the building of structures. 

 

Nitrogen is the most important inorganic nutrient for all plants. Nitrogen, in gas form, is actually the most abundant element present in the Earth’s atmosphere making up about 78 percent of it, with oxygen only making up 21 percent. 

 

Yet, despite nitrogen being so abundant, it is only present in the atmosphere as molecular nitrogen (N2), which is a very stable triple bond of nitrogen atoms and is inaccessible to plants. Therefore, nitrogen in its N2 form has to be changed before plants use it for growth. 

 

This process is called nitrogen-fixation. It is part of the nitrogen cycle, seen throughout nature. Nitrogen fixation is facilitated by bacteria that chemically alter the N2 by adding other elements such as hydrogen or oxygen, thereby creating new chemical compounds such as ammonia (NH3) and nitrate (NO3 – ) that plants can easily use. AND AMMONIUM

 

Also, atmospheric nitrogen can be fixed through an energy-intensive manufacturing process known as the Haber Process, used to produce synthetic fertilizers. 

 

Plants are able to use both ammonia and nitrates to perform their growth processes, but nitrates are more easily assimilated by their roots. EXPLAIN MORE….ADD IN AMMONIUM
Nitrifying bacteria, which live in diverse environments such as soil, sand, water and air, are an essential component of the nitrification process that converts plant and animal waste into accessible nutrients for plants. BUT THERE IS ALSO A RANGE OF OTHER SOIL PROCESSES JUST AS, OR EVEN MORE IMPORTANT

 

 This natural process of nitrification by bacteria that happens in soil also takes place in water in the same way. For aquaponics, the animal wastes are the fish excreta released in the culture tanks. The same nitrifying bacteria that live on land will also naturally establish in the water or on every wet surface, converting ammonia from fish waste into the easily assimilated nitrate for plants to use. Nitrification in aquaponic systems provides nutrients for the plants and eliminates ammonia and nitrite which are toxic (Figure 2.5).

 

2.2 THE BIOFILTER

 

Nitrifying bacteria are vital for the overall functioning of an aquaponic unit. Chapter 4 describes how the biofilter component for each aquaponic method works, and Chapter  5 describes the different bacteria groups that operate in an aquaponic unit. 

MENTION THAT THE BIOFILTER CONTAINS SAND…SAND NEEDS IT’S OWN SECTION AND SHOULD BE LINKED FROM HERE

 

Two major groups of nitrifying bacteria are involved in the nitrification process: 1) the ammonia-oxidizing bacteria (AOB), and 2) the nitrite-oxidizing bacteria (NOB) (Figure 2.6). They metabolize the ammonia in the following order: UPDATE THIS TO ADD INFORMATION ABOUT COMMAMOX, AND ALSO THE FACT THAT AMINO ACIDS AND OTHER INORGANIC FORMS CAN BE TAKEN UP BY PLANTS TOO

 

  1. AOB bacteria convert ammonia (NH₃) into nitrite (NO₂- ) 

 

  1. NOB bacteria then convert nitrite (NO₂- ) into nitrate (NO₃- ) As shown in the chemical symbols, the AOB oxidize (add oxygen to) the ammonia and create nitrite (NO₂- ) and the NOB further oxidize the nitrite (NO₂- ) into nitrate (NO₃- ). 

 

The genus Nitrosomonas is the most common AOB in aquaponics, and the genus Nitrobacter is the most common NOB; these names are frequently used interchangeably in the literature and are used throughout this publication. MENTION HOW THE CHEMICAL REACTION OF AMMONIA TO AMMONIUM IS PH DEPENDENT) – 

 

In summary, the ecosystem within the iAVs is totally reliant on the bacteria.

 

 If the bacteria are not present or if they are not functioning properly, ammonia concentrations in the water will kill the fish. It is vital to keep and manage a healthy bacterial colony in the system at all times in order to keep ammonia levels close to zero.

 

2.2.? The Detritus Layer 

Formation and Composition

The Detritus Layer forms within the furrows of the biofilter. When the system’s pump is activated, fish waste and nutrient laden water is transported into the furrows of the biofilter. This waste accumulates along the furrows, forming the Detritus Layer, which often appears dark in photographs. The layer is composed of organic matter that has been broken down by decomposers such as bacteria, fungi, and other microorganisms. It includes dead plant and animal material, fish waste, and uneaten food.

Role in Nutrient Cycling

The Detritus Layer serves as a vital source of nutrients for the rhizosphere, the area around the roots of plants. It provides food for the microorganisms in the rhizosphere, enabling the plants to access the nutrients they need for growth. The layer also acts as a filter for water passing through it, trapping pollutants before they can enter the aquatic environment below. Microbial activity within the layer helps to break down toxins from fish waste or other sources before they reach deeper levels in the system.

Algae in the Detritus Layer

The Detritus Layer also contains algae, which provides additional nutrition for the microorganisms in the rhizosphere. The algae do not compete with plants for nutrients. 

 

When the algae die, their nutrients become available to the microorganisms and plants in the rhizosphere. Some chemical compounds produced by certain types of algae may also be beneficial for plants and microbes, providing nutrition or protection against disease-causing organisms.

Mineralization Process

Mineralization occurs in the furrows of the detritus layer. This process involves the conversion of organic matter into inorganic forms that can be used by plants as nutrients. Bacteria and other microorganisms break down the organic solids in the detritus layer in the presence of oxygen, which accelerates the process. 

 

Each time the pump is activated, the fish waste is pumped up to the biofilter and into the furrows, where the organic solids are deposited. The intermittent irrigation regime exposes the detritus layer to an ongoing cycle of wetting and drying, which accelerates the decomposition of the organic solids, converting them into plant-available nutrients.

Maintenance of the Detritus Layer

The Detritus Layer requires minimal maintenance. However, in certain circumstances, such as when algae populations become excessive, the layer may need to be disturbed or ‘interrupted’ to prevent blockage of percolation. This can be done by scratching the surface with a stick or small hoe. If the system maintains active plant growth year-round, even this minimal maintenance may not be necessary.

 

2.2.3 Depth

 

This section provides a summary of research conducted on sand bed depths in iAVs and offers recommendations for optimal results.

 

Historical Research on Sand Bed Depths

 

Research on sand bed depths in iAVs has been conducted since the 1980s. In 1984, home aquarium filters with a depth of 6-8 inches were used to grow lettuce, dill, and basil. In 1985, a comparison with hydroponics used a sand bed depth of 8 to 10 inches (along a slope) plus 2-inch ridges and a 2-inch freeboard. This setup, which was 6 feet long, supported five species of plants, none of which were large. 

 

In 1986, a comparison with soil-based systems used sand beds up to 0.5 meters deep, including the ridge, slope, and freeboard. These 32-foot-long beds supported eight species of plants, half of which were large. In 1988-89, a 4×4 CBD ratio study used a minimum sand bed depth of 0.3 meters plus ridges, slope, and freeboard.

Recommended Sand Bed Depth

Based on the historical research, a minimum sand bed depth of 300mm (12 inches) is recommended for iAVs. While shallow beds of 200mm (8 inches) may be suitable for some plant species, this has yet to be tested. 

 

Any reduction in sand volume in the bed will result in a proportionate reduction in the micro-fauna in the bed. Deeper beds may be appropriate for very large plants and/or longer-term crops.

Considerations for Plant Root Development

Plants will develop only as much root volume as they need to support the aerial mass, not more than they need. In NFT and other various “hydroponic” techniques, plants do just fine, often far more than fine with only a few centimeters of root depth available. One should not extrapolate what is typically found in one circumstance/media to their requirements under entirely different conditions.

Flexibility in Sand Bed Depth

While a sand bed depth of 1/3 meter has been proven to be at least adequate for good results, it is not mandatory for every species of interest. If one wishes to increase the sand bed depth beyond what has been suggested, there is no good reason not to do so other than the additional cost and/or work involved. 

 

Whether said additional cost/work has a discernible positive impact on productivity remains to be anecdotally demonstrated much less clinically established. Deeper beds (increased volume) could actually benefit longer-term and vertical crops (greater rooting volumes). MAYBE REWRITE THE LAST SECTION

 

2.3 MAINTAINING A HEALTHY BACTERIAL COLONY

 

The major parameters affecting bacteria growth that should be considered when maintaining a healthy biofilter are adequate surface area BY USING SAND THAT HAS PASSED THE TESTS and appropriate water conditions.

 

2.3.1 Surface area

Bacterial colonies will thrive on any material, such as plant roots and along fish tank walls.

 

The total available area available for these bacteria will determine how much ammonia they are able to metabolize. AND THE OXYGEN AVAILABILITY – AS WELL AS THE REDUCTION OF AMMONIA BY CHEMICAL REACTION ALLOWS THE BACTERIA TO WORK BETTER

 

GPT-4

The Integrated AquaVegeculture System (iAVs) utilizes the unique properties of coarse sand and the biofilms that develop on them to create a highly efficient and organic growing method. The surface area of the sand and the biofilms play a crucial role in this system.

Coarse Sand and Surface Area

Coarse sand, used as the primary medium in iAVs, has a high surface area due to its roughness. This increased surface area provides an ample space for bacterial attachment and biofilm formation(4). The rough surfaces of the sand grains can also provide protection for bacteria against shear forces, thereby resisting the detachment of bound bacteria(4).

Biofilms and Their Role

Biofilms are complex structures formed by microorganisms that attach to surfaces and develop communities. These communities are differentiated from their suspended counterparts by the generation of an extracellular polymeric substance (EPS) matrix, reduced growth rates, and the up- and down- regulation of specific genes(2).

The development of a biofilm is a sequential process that starts with a loose association of the microorganisms to a surface, which then converts to strong adhesion. 

Once the microorganisms adhere to a surface, they often aggregate and form microcolonies that mature over time. The structured channels within the biofilm facilitate the exchanges of nutrients and byproducts between the embedded microorganisms and the external environment, which contributes to the microorganisms’ colonization growth and maturation(4).

Increased Surface Area through Biofilms

The formation of biofilms on the sand grains significantly increases the overall surface area in the iAVs system. This is because the biofilm, being a three-dimensional structure, adds to the surface area available for nutrient exchange and microbial activity(2).

Implications for iAVs

In the context of iAVs, the increased surface area provided by the coarse sand and the biofilms enhances the system’s efficiency. The biofilms house beneficial bacteria that contribute to the nutrient cycling in the system, aiding in the breakdown of fish waste into nutrients that the plants can absorb. The high surface area ensures a high level of contact between the water, nutrients, and plant roots, facilitating efficient nutrient uptake.

 

2.3.2 Water PH

 

The pH is how acidic or basic the water is. 

 

The pH level of the water has an impact on the biological activity of the nitrifying bacteria and their ability to convert ammonia and nitrite. The ranges for the two nitrifying groups below have been identified as ideal, yet the literature on bacteria growth also suggests a much larger tolerance range (6–8.5) because of the ability of bacteria to adapt to their surroundings.

 

However, for iAVs, a more appropriate pH range is 6.4 (+/-.04) because this range is better for the plants and fish (Chapter 3 discusses the compromise on water quality parameters). 

 

2.3.3 Water temperature

Water temperature is an important parameter for bacteria, and for iAVs in general. The ideal temperature range for bacteria growth and productivity is 17–34 °C. If the water temperature drops below 17  °C, bacteria productivity will decrease. Below 10 °C, productivity can be reduced by 50 percent or more. 

 

Low temperatures have major impacts on unit management during winter (see Chapter 8).

 

2.3.4 Dissolved oxygen

 

Nitrifying bacteria need an adequate level of dissolved oxygen (DO) in the water at all times in order to maintain high levels of productivity. Nitrification is an oxidative reaction, where oxygen is used as a reagent; without oxygen, the reaction stops. Optimum levels of DO are 4–8 mg/litre. Nitrification will decrease if DO concentrations drop below 2.0 mg/ litre. SHOULD THIS BE CHANGED SO THAT THE FOCUS IS ON ATMOSPHERIC OXYGEN INSTEAD – AND ONLY FOCUS ON THE DO WHEN DISCUSSING FISH?

 

2.3.5 Ultraviolet light

Nitrifying bacteria are photosensitive organisms, meaning that ultraviolet (UV) light from the sun is a threat. This is particularly the case during the initial formation of the bacteria colonies when a new system is set up. Once the bacteria have colonized a surface (3–5  days), UV light poses no major problem. A simple way to remove this threat is to cover the fish tank and filtration components with UV protective material while making sure no water is exposed to the sun, at least until the bacteria colonies are fully formed. 

 

Nitrifying bacteria will grow on material with a high surface area, sheltered using UV protective material, and under appropriate water conditions.

 

2.4 BALANCING THE ECOSYSTEM  

 

The term balancing is used to describe all the measures a farmer takes to ensure that the ecosystem of fish, plants and bacteria is at a dynamic equilibrium. It cannot be overstated that successful farming is primarily about maintaining a balanced ecosystem. 

 

Simply put, this means that there is a balance between the amount of fish, the amount of plants and the size of the biofilter, which really means the amount of bacteria. 

 

There are experimentally determined ratios between biofilter size  and fish TANK. It is unwise, and very difficult, to operate beyond these optimal ratios without disastrous consequences for the overall ecosystem.

 

2.4.1 Nitrate balance

 

The equilibrium in the iAVs can be compared with a balancing scale, where fish and plants are the weights standing at opposite arms. The balance’s arms are made of nitrifying bacteria. It is thus fundamental that the biofiltration is robust enough to support the other two components. 

 

This corresponds to the thickness of the lever in Figure 2.10. Note that the arms were not strong enough to support the amount of fish waste and that the arm broke. This means that the biofiltration was insufficient. If the fish biomass and biofilter size are in balance, the aquaponic unit will adequately process the ammonia into nitrate. However, if the plant component is undersized, then the system will start to accumulate nutrients (Figure 2.11). In practical terms, higher concentrations of nutrients are not harmful to fish nor plants, but they are an indication that the system is underperforming on the plant side. A common management mistake is when too many plants and too few fish are used, as seen in the third scenario shown in Figure 2.12. In this case, ammonia is processed by nitrifying bacteria, but the amount of resulting nitrate and other nutrients is insufficient to cover the plants’ needs. This condition eventually leads to a progressive reduction in nutrient concentrations and, consequently, plant yields. 

 

The major lesson from both examples is that achieving maximum production from aquaponics requires the maintaining of an appropriate balance between fish waste and vegetable nutrient demand, while ensuring adequate surface area to grow a bacterial colony in order to convert all the fish wastes. This balanced scenario is shown in Figure  2.13. This balance between fish and plants is also referred to as the biomass ratio. Successful aquaponic units have an appropriate biomass of fish in relation to the number of plants, or more accurately, the ratio of fish feed to plant nutrient demand is balanced. Although it is important to follow the suggested ratios for good aquaponic food production, there is a wide range of workable ratios, and experienced aquaponic farmers will notice how aquaponics becomes a self-regulating system. Moreover, the aquaponic system provides an attentive farmer with warning signs as the system begins to slip out of balance, in the form of water-quality metrics and the health of the fish and plants, all of which are discussed in detail throughout this publication.

 

2.4.2 Feed rate ratio

 

Many variables are considered when balancing a system, but extensive research has simplified the method of balancing a unit to a single ratio called the feed rate ratio.

 

The feed rate ratio is a summation of the three most important variables, which are: the daily amount of fish feed in grams per day, the plant type (vegetative vs. fruiting) and the plant growing space in square metres. This ratio suggests the amount of daily fish feed for every square metre of growing space. It is more useful to balance a system on the amount of feed entering the system than it is to calculate the amount of fish directly. 

 

By using the amount of feed, it is then possible to calculate how many fish based on their average daily consumption. The feed rate ratios will provide a balanced ecosystem for the fish, plants and bacteria, provided there is adequate biofiltration. 

 

Use this ratio when designing an iAVs. It is important to note that the feed rate ratio is only a guide to balancing, as other variables may have larger impacts at different stages in the season, such as seasonal changes in water temperature. The higher feed rate ratio for fruiting vegetables accounts for the greater amount of nutrients needed for these plants to produce flowers and fruits compared with leafy green vegetables. 

 

Along with the feed rate ratio, there are two other simple and complementary methods to ensure a balanced system: health check, and nitrogen testing.

 

2.4.3 Health check of fish and plants

Unhealthy fish or plants are often a warning that the system is out of balance. Symptoms of deficiencies on the plants usually indicate that not enough nutrients from fish waste are being produced. 

 

Nutrient deficiencies often manifest as poor growth, yellow leaves and poor root development, all of which are discussed in Chapter 6. In this case, the fish feed (if eaten by fish) or plants can be removed. 

 

Similarly, if fish exhibit signs of stress, such as gasping at the surface, rubbing on the sides of the tank, or showing red areas around the fins, eyes and gills, or in extreme cases dying, it is often because of a buildup of toxic ammonia or nitrite levels. 

 

This often happens when there is too much dissolved waste for the biofilter to process. Any of these symptoms in the fish or plants indicates that the farmer needs to actively investigate and rectify the cause ALL OF THIS IS NOT RELEVANT BUT SHOULD BE RE-WRITTEN FOR THOSE THAT HAVE NOT ADAPTED PROPER PROTOCOLS

 

2.4.4 Nitrogen testing

This method involves testing the nitrogen levels in the water using simple and inexpensive water test kits. If ammonia or nitrite are high (> 1 mg/litre), it indicates that the biofiltration is inadequate and the biofilter surface area available should be increased. 

 

Most fish are intolerant of these levels for more than a few days. An increasing level of nitrate is desired, and implies sufficient levels of the other nutrients required for plant growth. Fish can tolerate elevated levels of nitrate, but if the levels remain high (> 150 mg/litre) for several weeks some of the water should be removed and used to irrigate other crops. 

 

If nitrate levels are low (< 10 mg/litre) over a period of several weeks, the fish feed can be increased slightly to make sure there are enough nutrients for the vegetables. However, never leave uneaten fish feed in the aquaculture tank, so increasing the stocking density of the fish may be necessary. 

 

Alternatively, plants can be removed so that there are enough nutrients for those that remain. It is worthwhile and recommended testing for nitrogen levels every week to make sure the system is properly balanced. 

 

Moreover, nitrate levels are an indicator of the level of other nutrients in the water. Again, all the calculations and ratios mentioned above, including fish stocking, planting capacity and biofilter sizes, are explained in much greater depth in the following chapters (especially in Chapter  8). 

 

The aim of this section was to provide an understanding of how vital it is to balance the ecosystem within iAVs and to highlight the simple methods and strategies to do so.

 

2.5-CHAPTER SUMMARY 

  • iAVs is a production system that combines aquaculture with horticulture in one recirculating system.

 

  • Nitrifying bacteria convert fish waste (ammonia) into plant food (nitrate). 
  • The  most important part of iAVs, the bacteria, is invisible to the naked eye.
  • The key factors for maintaining healthy bacteria are water temperature, pH, dissolved oxygen and adequate surface area on which the bacteria can grow. 

 

  • Successful iAVs are balanced. The feed rate ratio is the main guideline to balance the amount of fish feed to plant growing area, which is measured in grams of daily feed per square metre of plant growing space. 

 

  • The feed rate ratio for leafy vegetables is 40–50  g/m2 /day; fruiting vegetables require 50–80 g/m2 /day.
  • Daily health monitoring of the fish and the plants will provide feedback on the balance of the system. Disease, nutritional deficiencies and death are symptoms of an unbalanced system. 

 

  • Water testing will provide information on the balance of the system. High ammonia or nitrite indicates insufficient biofiltration; low nitrate indicates too many plants or not enough fish; increasing nitrate is desirable and indicates adequate nutrients for the plants, though water needs to be exchanged when nitrate is greater than 150 mg/litre.

 

3. Water quality 

 

This chapter describes the basic concepts of managing the water within an iAVs. The chapter begins by setting the framework and comments on the importance of good water quality for successful iAVs food production. 

 

Following this, the major water quality parameters are discussed in detail. Management and manipulation of some of the parameters are discussed, especially in regard to sourcing water when replenishing an iAVs. 

 

Water is the life-blood of an iAVs. It is the medium through which all essential macro- and micronutrients are transported to the plants, and the medium through which the fish receive oxygen. Thus, it is one of the most important topics to understand.

 

Five key water quality parameters are discussed: dissolved oxygen (DO), pH, temperature, total nitrogen, and water alkalinity. Each parameter has an impact on all three organisms in the unit (fish, plants and bacteria), and understanding the effects of each parameter is crucial. 

 

Although some aspects of the knowledge on water quality and water chemistry needed for iAVs seem complicated, the actual management is relatively simple with the help of simple test kits. 

 

Water testing is essential to keeping good water quality in the system. 

A LOT OF THIS NEEDS TO BE CHANGED BECAUSE IAVS WAS MADE FOR PEOPLE TO NOT HAVE TO KNOW OR DO ALL THESE OTHER COMPLICATED THINGS

 

3.1 WORKING WITHIN THE TOLERANCE RANGE FOR EACH ORGANISM

 

As discussed in Chapter 2, iAVs is primarily about balancing an ecosystem of three groups of organisms: fish, plants and bacteria (Figure 3.2). 

 

Each organism in an aquaponic unit has a specific tolerance range for each parameter of water quality (Table 3.1). The tolerance ranges are relatively similar for all three organisms, but there is need for compromise and therefore some organisms will not be functioning at their optimum level. 

 

Table 3.2 illustrates the ideal compromise for iAVs that is needed for the key water quality parameters.

 

The two most important parameters to balance are pH and temperature. It is recommended that the pH be maintained at a compromised level of 6.4 +/-0.4. 

 

The general temperature range is 18–30  °C, and should be managed in regard to the target fish or plant species cultivated; bacteria thrive throughout this range. It is important to choose appropriate pairings of fish and plant species that match well with the environmental conditions. 

 

Chapter 7 and Appendix 1 describe the optimal growing temperatures of common fish and plants. The overall goal is to maintain a healthy ecosystem with water quality parameters that satisfy the requirements for growing fish, vegetables and bacteria simultaneously. 

 

There are occasions when the water quality may need to be actively manipulated to meet these criteria and keep the system functioning properly.

 

3.2 THE FIVE MOST IMPORTANT WATER QUALITY PARAMETERS

3.2.1 Oxygen

Oxygen is essential for all three organisms involved in iAVs; plants, fish and bacteria all need oxygen to live. The DO level describes the amount of molecular oxygen within the water, and it is measured in milligrams per litre. 

 

It is the water quality parameter that has the most immediate and drastic effect in iAVs. Indeed, fish may die within hours when exposed to low DO within the fish tanks. Thus, ensuring adequate DO levels is crucial to aquaponics

 

Although monitoring DO levels is very important, it can be challenging because accurate DO measuring devices can be very expensive or difficult to find. It is often sufficient for small-scale units to instead rely on frequent monitoring of fish behaviour and plant growth, and ensuring water and air pumps are in proper working order. MAY NEED TO ADD BATTERY BACKUP AND MENTION CASCADE AERATORS. Oxygen dissolves directly into the water surface from the atmosphere. MENTION DIFFERENCE BETWEEN OXYGEN IN AIR CMPARED TO THAT IN WATER, MAY EVEN NEED TO REWRITE THIS SECTION AS IT IS SORT OF TRYING TO SOLVE A PROBLEM THAT IAVS ALREADY SOLVED. In natural conditions, fish can survive in such water, but in intensive production systems with higher fish densities, this amount of DO diffusion is insufficient to meet the demands of fish, plants and bacteria. THIS NEEDS TO BE CHANGED AND RE-WRITTEN BECAUSE IN IAVS THE IDEA IS TO NEVER OVER STOCK AND AS SUCH THE LINE ABOUT BEING INSUFFICIENT IS INCORRECT. Thus, the DO needs to be supplemented through management strategies

 

In addition to cascade aerators, two other strategies for small-scale systems are to use water pumps to create dynamic water flow, and to use aerators that produce air bubbles in the water. Water movement and aeration are critical aspects of every iAVs, and their importance cannot be overstressed. 

 

These topics, including methods of design and redundancy, are discussed further in Chapter  4. The optimum DO levels for each organism to thrive are 5–8 mg/litre (Figure 3.3). Some species of fish, including carp and tilapia, can tolerate DO levels as low as 2–3 mg/litre, but it is much safer to have the levels higher for iAVs, as all three organisms demand the use of the DO in the water. THIS IS NOT THE CASE SO MUCH WITH THE PLANTS AND THE BACTERIA. 

 

Water temperature and DO have a unique relationship that can affect food production. As water temperature rises, the solubility of oxygen decreases. Put another way, the capacity of water to hold DO decreases as temperature increases; warm water holds less oxygen than does cold water (Figure  3.4).  IS THIS WHERE WE MENTION THE DIFFERENCE BETWEEN MAXIMUM OXYGEN THAT CAN BE DISSOLVED IN WATER COMPARED TO THAT WHAT IS AVAILABLE IN AIR

 

As such, it is recommended that aeration be increased using air pumps in warm locations or during the hottest times of the year, especially if raising delicate fish.

 

3.2.2 PH

 

A general knowledge of pH is useful for managing iAVs. 

 

The pH of a solution is a measure of how acidic or basic the solution is on a scale ranging from 1 to 14. A pH of 7 is neutral; anything below 7 is acidic, while anything above 7 is basic. The term pH is defined as the amount of hydrogen ions (H+) in a solution; the more hydrogen ions, the more acidic. 

 

Two important aspects of the pH scale are illustrated in Figure 3.5.

  •  The pH scale is negative a pH of has fewer hydrogen ions than a pH of 6. 
  • The pH scale is logarithmic a pH of has10 times fewer hydrogen ions than a pH of 6, 100 times fewer than a pH of 5, and 1 000 times fewer than a pH of 4. 

 

For example, if the pH of an iAVs is recorded as 7, and later the value is recorded as 8, the water now has ten times fewer freely associated H+ ions because the scale is negative and logarithmic. 

 

It is important to be aware of the logarithmic nature of the pH scale because it is not necessarily intuitive. For the previous example, if a later reading showed the pH to be 9, the problem would be 100 times worse, and therefore hypercritical, instead of just being two times worse.

 

Importance of pH

The pH of the water has a major impact on all aspects of iAVs, especially the plants and bacteria. For plants, the pH controls the plants’ access to micro- and macronutrients.

 

At a pH of 6.0–6.5, all of the nutrients are readily available, but outside this range the nutrients become difficult for plants to access. 

 

In fact, a pH of 7.5 can lead to nutrient deficiencies of iron, phosphorus and manganese. This phenomenon is known as nutrient lock-out and is discussed in Chapter 6. Nitrifying bacteria experience difficulty below a pH of 6, and the bacteria’s capacity to convert ammonia into nitrate reduces in acidic, low pH conditions. MENTION A SECTION ABOUT THE ABUNDANCE OF OXYGEN AND REDUCTION OF AMMONIA THAT CAUSES BACTERIA TO THRIVE DESPITE BEING IN AN ACIDIC ENVIRONMENT.  

 

This can lead to reduced biofiltration, and as a result the bacteria decrease the conversion of ammonia to nitrate, and ammonia levels can begin to increase, leading to an unbalanced system stressful to the other organisms. MENTION THE CHEMICAL REACTION OF AMMONIA TO AMMONIUM THAT ACTS AS A BUFFER TO PROTECT AGAINST AMMONIA SPIKES, MAY NEED TO REWRITE SECTION IF IT IS REDUNDANT IN IAVS – NEED TO SEE IF IT IS IN SECTION 3.4 TO AVOID DUPLICATE CONTENT.  

 

Fish have specific tolerance ranges for pH as well, but most fish used in iAVs have a pH tolerance range of 6.0–8.5. 

 

However, the pH affects the toxicity of ammonia to fish, with higher pH leading to higher toxicity. This concept is more fully discussed in the Section 3.4. In conclusion, the ideal iAVs water is slightly acidic, with an optimum pH range of 6.4 (+/-.04). This range will keep the bacteria functioning at a high capacity, while allowing the plants full access to all the essential micro- and macronutrients. 

 

pH values between 5.5 and 7.5 require management attention and manipulation through slow and measured means, discussed in Section 3.5 and in Chapter 6. However, 

 

A pH lower than 5 or above 8 can quickly become a critical problem for the entire ecosystem and thus immediate attention is required. There are many biological and chemical processes that take place in an aquaponics system that affect the pH of the water, some more significantly than others, including: the nitrification process; fish stocking density; and phytoplankton.

 

The nitrification process

The nitrification process of bacteria naturally lowers the pH of an aquaponic system. Weak concentrations of nitric acid are produced from the nitrification process as the bacteria liberate hydrogen ions during the conversion of ammonia to nitrate. Over time, the aquaponic system will gradually become more acidic primarily as a result of this bacterial activity. 

NOT APPLICABLE IN IAVS, NEED TO ADD A SECTION TO EXPLAIN WHY

 

Fish stocking density

The respiration, or breathing, of the fish releases carbon dioxide (CO2) into the water. 

 

This carbon dioxide lowers pH because carbon dioxide converts naturally into carbonic acid (H2CO3) upon contact with water. 

 

The higher the fish stocking density of the unit, the more carbon dioxide will be released, hence lowering the overall pH level. This effect is increased when the fish are more active, such as at warmer temperatures. NEED TO REWRITE SO THE TERM ‘STOCKING DENSITY’ IS REPLACED

 

Phytoplankton

Respiration by fish lowers the pH by releasing carbon dioxide into the water; conversely, the photosynthesis of plankton, algae and aquatic plants remove carbon dioxide from the water and raises the pH. The effect of algae on pH follows a daily pattern, where the pH rises during the day as the aquatic plants photosynthesize and remove carbonic acid, and then falls overnight as the plants respire and release carbonic acid. Therefore, the pH is at a minimum at sunrise and a maximum at sunset. In standard RAS or aquaponic systems, phytoplankton levels are usually low and, therefore, the daily pH cycle is not affected. However, some aquaculture techniques, such as pond aquaculture and some fish breeding techniques, deliberately use phytoplankton, so the time of monitoring should be chosen wisely. NOT SURE IF THIS SECTION IS RELEVANT 

 

3.2.3 Temperature 

 

Water temperature affects all aspects of iAVs. 

 

Overall, a general compromise range is 18–30  °C. Temperature has an effect on DO as well as on the toxicity (ionization) of ammonia; high temperatures have less DO and more unionized (toxic) ammonia. 

 

Also, high temperatures can restrict the absorption of calcium in plants. The combination of fish and plants should be chosen to match the ambient temperature for the systems’ location, and changing the temperature of the water can be very energy-intensive and expensive. Warm-water fish (e.g. tilapia, common carp, catfish) and nitrifying bacteria thrive in higher water temperatures of 22–29 °C, as do some popular vegetables such as okra, Asian cabbages, and basil. 

 

Contrarily, some common vegetables such as lettuce, Swiss chard and cucumbers grow better in cooler temperatures of 18–26 °C, and cold-water fish such as trout will not tolerate temperatures higher than 18 °C. 

 

For more information on optimal temperature ranges for individual plants and fish, see Chapters 6 and 7 on plant and fish production, respectively, and Appendix 1 for key growing information on 12 popular vegetables. 

 

Although it is best to choose plants and fish already adapted to the local climate, there are management techniques that can minimize temperature fluctuations and extend the growing season. 

 

Systems are also more productive if the daily, day to night, temperature fluctuations are minimal. Therefore, the water surface itself in the fish tank should be shielded from the sun using shade structures. 

 

Similarly, the unit can be thermally protected using insulation against cool night temperatures wherever these occur. 

 

Alternatively, there are methods to passively heat an iAVs using greenhouses or solar energy with coiled agricultural pipes, which are most useful when temperatures are lower than 15  °C; these methods are described in more detail in Chapters 4 and 9. 

 

It is also possible to adopt a fish production strategy to cater for temperature differences between winter and summer, particularly if winter has average temperatures of less than 15  °C for more than three months. 

 

Generally, this means cold-adapted fish and plants are grown during winter, and the system is changed over to warm-water fish and plants as the temperatures climb again in spring. 

 

If these methods are not feasible during cold winter seasons, it is also possible to simply harvest the fish and plants at the start of winter and shut down the systems until spring. 

 

During summer seasons with extremely warm temperatures (more than 35 °C), it is essential to select the appropriate fish and plants to grow (see Chapters 6 and 7) and shade all containers and the plant growing space.

 

3.2.4 Total nitrogen: ammonia, nitrite, nitrate

Nitrogen is the fourth crucial water quality parameter. 

 

It is required by all life, and part of all proteins. Nitrogen originally enters an iAVs from the fish feed, usually labelled as crude protein and measured as a percentage. Some of this protein is used by the fish for growth, and the remainder is released by the fish as waste. 

 

This waste is mostly in the form of ammonia (NH3) and is released through the gills and as urine. Solid waste is also released, some of which is converted into ammonia by microbial activity. 

 

This ammonia is then nitrified by bacteria, discussed in Section 2.1, and converted into nitrite (NO2 – ) and nitrate (NO3 – ). Nitrogenous wastes are poisonous to fish at certain concentrations, although ammonia and nitrite are approximately 100 times more poisonous than nitrate. Although toxic to fish, nitrogen compounds are nutritious for plants, and indeed are the basic component of plant fertilizers. All three forms of nitrogen (NH3, NO2 – and NO3 – ) can be used by plants, but nitrate is by far the most accessible. 

 

In a fully functioning iAVs, ammonia and nitrite levels should be close to zero, or at most 0.25–1.0 mg/litre. CHECK THIS AGAINST THE RESEARCH LEVELS The bacteria present in the biofilter should be converting almost all the ammonia and nitrite into nitrate before any accumulation can occur.

 

Impacts of high ammonia

Ammonia is toxic to fish. 

 

Tilapia and carp can show symptoms of ammonia poisoning at levels as low as 1.0 mg/litre. Prolonged exposure at or above this level will cause damage to the fishes’ central nervous system and gills, resulting in loss of equilibrium, impaired respiration and convulsions. 

 

The damage to the gills, often evidenced by red colouration and inflammation on the gills, will restrict the correct functioning of other physiological processes, leading to a suppressed immune system and eventual death.

 

Other symptoms include red streaks on the body, lethargy and gasping at the surface for air. At higher levels of ammonia, effects are immediate and numerous deaths can occur rapidly. However, lower levels over a long period can still result in fish stress, increased incidence of disease and more fish loss. 

 

As discussed above, ammonia toxicity is actually dependent on both pH and temperature, where higher pH and water temperature make ammonia more toxic. Chemically, ammonia can exist in two forms in water, ionized and unionized. 

 

Together, these two forms together are called total ammonia nitrogen (TAN), and water testing kits are unable to distinguish between the two. In acidic conditions, the ammonia binds with the excess hydrogen ions (low pH means a high concentration of H+) and becomes less toxic. 

 

This ionized form is called ammonium. However, in basic conditions (high pH, above 7), there are not enough hydrogen ions and the ammonia remains in its more toxic state, and even low levels of ammonia can be highly stressful for the fish. 

 

This problem is exacerbated in warm water conditions. Activity of nitrifying bacteria declines dramatically at high levels of ammonia. Ammonia can be used as an antibacterial agent, and at levels higher than 4 mg/litre it will inhibit and drastically reduce the effectiveness of the nitrifying bacteria. 

 

This can result in an exponentially deteriorating situation when an undersized biofilter is overwhelmed by ammonia, the bacteria die and the ammonia increases even more.

 

Impacts of high nitrite 

 

Nitrite is toxic to fish. Similar to ammonia, problems with fish health can arise with concentrations as low as 0.25 mg/litre. 

 

High levels of NO2 – can immediately lead to rapid fish deaths. 

 

Again, even low levels over an extended period can result in increased fish stress, disease and death. 

 

Toxic levels of NO2 – prevent the transport of oxygen within the bloodstream of fish, which causes the blood to turn a chocolate-brown colour and is sometimes known as “brown blood disease”. 

This effect can be seen in fish gills as well. Affected fish exhibit similar symptoms to ammonia poisoning, particularly where fish appear to be oxygen deprived, seen gasping at the surface even in water with a high concentration of DO. 

 

Fish health is covered in more detail in Chapter 7.

 

Impacts of high nitrate 

 

Nitrate is a far less toxic than the other forms of nitrogen. 

It is the most accessible form of nitrogen for plants, and the production of nitrate is the goal of the biofilter. Fish can tolerate levels of up to 300 mg/litre, with some fish tolerating levels as high as 400 mg/litre. 

 

High levels (> 250 mg/litre) will have a negative impact on plants, leading to excessive vegetative growth and hazardous accumulation of nitrates in leaves, which is dangerous for human health. 

 

It is recommended to keep the nitrate levels at 5–150 mg/litre and to exchange water when levels become higher. 

 

3.2.5 Water hardness 

 

The final water quality parameter is water hardness. 

 

There are two major types of hardness: general hardness (GH), and carbonate hardness (KH). General hardness is a measure of positive ions in the water. 

 

Carbonate hardness, also known as alkalinity, is a measure of the buffering capacity of water. The first type of hardness does not have a major impact on iAVs NEED TO CONFIRM, but KH has a unique relationship with pH that deserves further explanation.

 

General hardness 

 

General hardness is essentially the amount of calcium (Ca2+), magnesium (Mg2+) and, to a lesser extent, iron (Fe+) ions present in water. It is measured in parts per million (equivalent to milligrams per litre). 

 

High GH concentrations are found in water sources such as limestone-based aquifers and/or river beds, as limestone is essentially composed of calcium carbonate (CaCO3). Both Ca2+ and Mg2+ ions are essential plant nutrients, and they are taken up by plants as the water flows through the biofilter. 

 

Rainwater has low water hardness because these ions are not found in the atmosphere. Hard water can be a useful source of micronutrients for iAVs, and has no health effects on the organisms. 

 

In fact, the presence of calcium in the water can prevent fish from losing other salts and lead to a healthier stock. CHECK

 

Carbonate hardness or alkalinity 

 

Carbonate hardness is the total amount of carbonates (CO3 2-) and bicarbonates (HCO3 – ) dissolved in water.

 

It is also measured in milligrams of CaCO3 per litre. In general, water is considered to have high KH at levels of 121–180 mg/litre. Water sourced from limestone bedrock wells/aquifers will normally have a high carbonate hardness of about 150–180 mg/litre. 

 

Carbonate hardness in water has an impact on the pH level. Simply put, KH acts as a buffer (or a resistance) to the lowering of pH. 

 

Carbonate and bicarbonate present in the water will bind to the H+ ions released by any acid, thus removing these free H+ ions from the water. 

 

Therefore, the pH will stay constant even as new H+ ions from the acid are added to the water. This KH buffering is important, because rapid changes in pH are stressful to the entire iAVs ecosystem. The nitrification process generates nitric acid (HNO3), as discussed in Section  3.2.2, 

 

UNLESS THAT SECTION IS REMOVED! which is dissociated in water in its two components, hydrogen ions (H+) and nitrate (NO3 – ), with the latter used as source of nutrients for plants. However, with adequate KH the water does not actually become more acidic. If no carbonates and bicarbonates were present in the water, the pH would quickly drop in the aquaponic unit. The higher the concentration of KH in the water, the longer it will act as a buffer for pH to keep the system stable against the acidification caused by the nitrification process.  NOT RELEVANT IN IAVS?

 

The next section describes this process in more detail. It is a rather complicated process but it is important to understand for iAVs practitioners where the available water is naturally very hard (which is normally the case in regions with limestone or chalk bedrock), as pH manipulation will become a vital part of unit management. 

 

Section 3.5 contains specific techniques of pH manipulation. 

The summary following the extended description will list what is essential for all practitioners to know regarding hardness. As mentioned above, the constant nitrification in an aquaponic unit produces nitric acid and increases the number of H+ ions, which would lower the pH in the water. If no carbonates or bicarbonates are present to buffer the H+ ions in the water, the pH will quickly drop as more H+ ions are added into the water. Carbonates and bicarbonates, as shown in Figure 3.6, bind the hydrogen ions (H+) released from the nitric acid and maintain a constant pH by balancing the surplus of H+ with the production of carbonic acid, which is a very weak acid. The H+ ions remain bound to the compound and are not free in the water. Figure 3.7 shows in more detail the bonding process occurring with nitric acid. It is essential for aquaponics that a certain concentration of KH is present at all times in the water, as it can neutralize the acids created naturally and keep the pH constant. Without adequate KH, the unit could be subjected to rapid pH changes that would have negative impacts on the whole system, especially the fish. However, KH is present in many water sources. Replenishing the unit with water from these sources will also replenish the levels of KH. However, rainwater is low in KH, and in rainfed systems it is helpful to add external sources of carbonate, as explained below. CHECK TO SEE IF ANY OF THIS IS ACTUALLY NEEDED

 

FIGURE 3.6 AND 3.7 NOT ADDED

 

Summary of essential points on hardness 

 

General Hardness (GH) is the measurement of positive ions, especially calcium and magnesium. 

 

Carbonate Hardness (KH) measures the concentration of carbonates and bicarbonates that buffer the pH (create resistance to pH change). 

 

Hardness can be classified along the water hardness scale as shown below: 

 

The optimum level of both hardness types for iAVs is about 60–140 mg/litre. CHECK THIS  It is not vital to check the levels in the unit, but it is important that the water being used to replenish the unit has adequate concentrations of KH to continue neutralizing the nitric acid produced during the nitrification process and to buffer the pH at its optimum level (6–7).

3.3 OTHER MAJOR COMPONENTS OF WATER QUALITY: ALGAE AND PARASITES 

 

3.3.1 Photosynthetic activity of algae

 

WILL NEED TO ADD A SECTION ON DETRITUS – ALSO ADD NOTES FROM RESEARCH ABOUT TILAPIA GRAZING ON ALGAE

 

Photosynthetic growth and activity by algae in the fish tank affect the water quality parameters of pH, DO, and nitrogen levels. 

 

Algae are a class of photosynthetic organisms that are similar to plants, and they will readily grow in any body of water that is rich in nutrients and exposed to sunlight. Some algae are microscopic, single-celled organisms called phytoplankton, which can colour the water green (Figure  3.8). 

 

Macroalgae are much larger, commonly forming filamentous mats attached to the bottoms and sides of tanks (Figure 3.9). For iAVs, it is important to prevent algae growing because they are problematic for several reasons. ARE THEY? OR IS IT ONLY WHEN IN EXCESS? 

 

First, they will consume the nutrients in the water and compete with the target vegetables. In addition, algae act as both a source and sink of DO, producing oxygen during the day through photosynthesis and consuming oxygen at night during respiration. They can dramatically reduce the DO levels in water at night, so causing fish death. 

 

This production and consumption of oxygen is related to the production and consumption of carbon dioxide, which causes daily shifts in pH as carbonic acid is either removed (daytime – higher water pH) from or returned (night time – lower water pH) to the system. 

 

Finally, filamentous algae can clog drains and block filters within the unit, leading to problems with water circulation. Brown filamentous algae can also grow on the roots of the hydroponic plants, especially in deep water culture, and negatively affects plant growth. However, 

 

Some aquaculture operations benefit greatly from culturing algae for feed, referred to as green-water culture, including tilapia breeding, shrimp culture, and biodiesel production, but these topics are not directly related to iAVs and are not discussed here. 

 

Preventing algae is relatively easy. All water surfaces should be shaded. 

 

Shade cloth, tarps, woven palm fronds or plastic lids should be used to cover fish tanks and biofilters such that no water is in direct contact with sunlight. This will inhibit algae from blooming in the fish tank.

 

3.3.2 Parasites, bacteria and other small organisms living in the water 

 

iAVs is an ecosystem comprised mainly of fish, bacteria, and plants. 

 

However, over time, there may be many other organisms contributing to this ecosystem. Some of these organisms with be helpful, such as earthworms, and facilitate the decomposition of fish waste. 

 

Others are benign, neither helping nor harming the system, such as various crustaceans, living in the biofilters. 

 

Others are threats; parasites, pests and bacteria are impossible to avoid completely because iAVs is not a sterile endeavour. 

 

The best management practice to prevent these small threats from becoming dangerous infestations is to grow healthy, stress-free fish and plants by ensuring highly aerobic conditions with access to all essential nutrients. WHICH IS PART OF THE DESIGN OF IAVS

 

In this way, the organisms can stave off infection or disease using their own healthy immune systems. Chapters 6 and 7 discuss additional management of fish and plant diseases, and 

 

Chapter 8 covers food safety and other biothreats in more detail.

 

3.4 SOURCES OF WATER

 

 On average, an iAVs uses 1–3 percent of its total water volume per day, CHECK AND CONFIRM TO THE RESEARCH depending on the type of plants being grown and the location. 

 

Water is used by the plants through natural evapotranspiration as well as being retained within the plant tissues. 

 

Additional water is lost from direct evaporation and splashing. As such, the unit will need to be replenished periodically. The water source used will have an impact on the water chemistry of the unit. Below is a description of some common water sources and the common chemical composition of that water. 

 

New water sources should always be tested for pH, hardness, salinity, chlorine and for any pollutants in order to ensure the water is safe to use. 

 

Here, it is important to consider an additional water quality parameter: salinity. Salinity indicates the concentration of salts in water, which include table salt (sodium chloride  – NaCl), as well as plant nutrients, which are in fact salts. 

 

Salinity levels will have a large bearing when deciding which water to use because high salinity can negatively affect vegetable production, especially if it is of sodium chloride origin, as sodium is toxic for plants. Water salinity can be measured with an electrical conductivity (EC) meter, a total dissolved solids (TDS) meter, a refractometer, or a hydrometer or operators can refer to local government reports on water quality. Salinity is measured either as conductivity, or how much electricity will pass through the water, as units of microSiemens per centimetre (μS/cm), or in TDS as parts per thousand (ppt) or parts per million (ppm or mg/litre). 

 

For reference, seawater has a conductivity of 50 000 μS/ cm and TDS of 35 ppt (35 000 ppm). Although the impact of salinity on plant growth varies greatly between plants (Section 9.4.2, Appendix 1), it is recommended that low salinity water sources be used. Salinity, generally, is too high if sourcing water has a conductivity more than 1 500 μS/cm or a TDS concentration of more than 800 ppm. 

 

Although EC and TDS meters are commonly used for hydroponics to measure the total amount of nutrient salts in the water, these meters do not provide a precise reading of the nitrate levels, which can be better monitored with nitrogen test kits.

 

3.4.1 Rainwater 

 

Collected rainwater is an excellent source of water for iAVs.

 

 The water will usually have a neutral pH and very low concentrations of both types of hardness (KH and GH) and almost zero salinity, which is optimal to replenish the system and avoid long-term salinity buildups. 

 

However, in some areas affected by acid rain as recorded in a number of localities in Eastern Europe, eastern United States of America and areas of Southeast Asia, rainwater will have an acidic pH. 

 

Generally, it is good practice to buffer rainwater and increase the KH as indicated in Section 3.5.2. In addition, rainwater harvesting will reduce the overhead costs of running the unit, and it is more sustainable.

 

3.4.2 Cistern or aquifer water

 

 The quality of water taken from wells or cisterns will largely depend on the material of the cistern and bedrock of the aquifer. 

 

If the bedrock is limestone, then the water will probably have quite high concentrations of hardness, which may have an impact on the pH of the water.

 

Aquifers on coral islands often have saltwater intrusion into the freshwater lens, and can have salinity levels too high for iAVs, so monitoring is necessary and rainwater collection or reverse osmosis filtration may be better options.

 

3.4.3 Tap or municipal water 

 

Water from the municipal supplies is often treated with different chemicals to remove pathogens. The most common chemicals used for water treatment are chlorine and chloramines. 

 

These chemicals are toxic to fish, plants and bacteria; these chemicals are used to kill bacteria in water and as such are detrimental to the health of the overall iAVs ecosystem. 

 

Chlorine test kits are available; and if high levels of chlorine are detected, the water needs to be treated before being used. The simplest method is to store the water before use, thereby allowing all the chlorine to dissipate into the atmosphere. This can take upwards of 48 hours, but can occur faster if the water is heavily aerated with air stones. 

 

Chloramines are more stable and do not off-gas as readily. If the municipality uses chloramines, it may be necessary to use chemical treatment techniques such as charcoal filtration or other dechlorinating chemicals. 

 

Even so, off-gassing is usually enough in small-scale units using municipal water. A good guideline is to never replace more than 10 percent of the water without testing and removing the chlorine first. 

 

Moreover, the quality of the water will depend on the bedrock where the initial water is sourced. Always check new sources of water for hardness levels and pH, and use acid if appropriate and necessary to maintain the pH within the optimum levels indicated above.

 

3.4.4 Filtered water 

 

Depending on the type of filtration (i.e. reverse osmosis or carbon filtering), filtered water will have most of the metals and ions removed, making the water very safe to use and relatively easy to manipulate. 

 

3.5 MANIPULATING PH

 

 There are simple methods to manipulate the pH of source water to be used in an iAVs if it is not at the ideal range of 6.4 +/-0.4. 

 

3.5.1 Lowering pH with acid

 

Adding acid directly to an iAVs is dangerous. The danger is that at first the acid reacts with buffers and no pH change is noticed. More and more acid is added with no pH change, until finally all the buffers have reacted and the pH drops drastically, often resulting in a terrible and stressful shock to the system. 

 

It is better practice, if necessary to add acid, to treat a reservoir of this resupply water with acid, and then add the treated water to the system (Figure 3.10). This removes the risk to the system if too much acid is used. The acid should always be added to a volume of resupply water, and extreme care should be used not to add too much acid to the system. If the system is designed with an automatic water supply line it may be necessary to add acid directly to the system, but the danger is increased. 

 

Phosphoric acid (H3PO4) can be used to lower the pH. Phosphoric acid is a relatively mild acid. It can be found in food-grade quality from hydroponic or agricultural supply stores under various trade names. 

 

Phosphorus is an important macronutrient for plants, but overuse of phosphoric acid can lead to toxic concentration of phosphorous in the system. In situations with extremely hard and basic source water  (high KH, high pH), sulphuric acid (H2SO4) has been used. However, owing to its high corrosiveness and even higher level of danger, its use is not recommended to beginners. 

 

Nitric acid (HNO3) has also been used as a relatively neutral acid. Citric acid, while tempting to use, is antimicrobial and can kill the bacteria in the biofilter; citric acid should not be used. 

 

Concentrated acids are dangerous, both to the system and to the operator. Proper safety precautions should be used, including safety goggles and gloves (Figure 3.11). Never add water to acid, always add acid to water. 

 

3.5.2 Increasing pH with buffers or bases

 

Commonly used bases are potassium hydroxide (KOH) and calcium hydroxide (Ca(OH)2). These bases are strong, and should be added in the same way as acids; always change pH slowly. However, a safer and easier solution is to add calcium carbonate (CaCO3) or potassium carbonate (K2CO3), which will increase both the KH and pH. 

 

The choice of the bases and buffers can also be driven by the type of plants growing in the system, as each of these compounds adds an important macronutrient. Leafy vegetables can be favoured by calcium bases to avoid tip burns on leaves; while potassium is optimal in fruit plants to favour flowering, fruit settings and optimal ripening. 

 

Sodium bicarbonate (baking soda) is often used to increase carbonate hardness but should never be used in iAVs because of the resulting increase in sodium, which is detrimental to the plants.

 

3.6 WATER TESTING 

 

In order to maintain good water quality in iAVs, it is recommended to perform water tests once per week to make sure all the parameters are within the optimum levels. 

 

However, a mature and seasoned iAVs will have consistent water chemistry and does not need to be tested as often. In these cases, water testing is only needed if a problem is suspected. In addition, daily health monitoring of the fish and the plants growing in the unit will indicate if something is wrong, although this method is not a substitution for water testing. 

 

Access to simple water tests are strongly recommended for every iAVs. Colour-coded freshwater test kits are readily available and easy to use (Figure 3.13). 

 

These kits include tests for pH, ammonia, nitrite, nitrate, GH, and KH. Each test involves adding 5–10 drops of a reagent into 5 millilitres of iAVs water; each test takes no more than five minutes to complete. 

 

Other methods include digital pH or nitrate meters (relatively expensive and very accurate) or water test strips (cheapest and moderately accurate, Figure 3.14).

 

The most important tests to perform weekly are pH, nitrate, carbonate hardness and water temperature, because these results will indicate whether the system is in balance. 

 

The results should be recorded each week in a dedicated logbook so trends and changes can be monitored throughout growing seasons. Testing for ammonia and nitrite is also extremely helpful in order to diagnose problems in the unit, especially in new units or if an increase in fish mortality raises toxicity concerns in an ongoing system. 

 

Although they are not essential for weekly monitoring in established units, they can provide very strong indicators of how well the bacteria are converting the fish waste and the health of the biofilter. 

 

Testing for ammonia and nitrate are the first action if any problems are noticed with the fish or plants.

 

3.7 Evaporative Loss Management in iAVs

 

Integrated AquaVegeculture Systems (iAVs) effectively manage evaporative loss through a combination of unique design features and operational practices. This section explores the factors contributing to this efficiency and dispels some common misconceptions.

Transpiration and Biomass Incorporation

A significant portion of water loss in iAVs is attributed to transpiration, a natural and unavoidable process that varies by location, season, and crop type. Additionally, a considerable fraction of water is incorporated into plant tissues, contributing to biomass production. These factors are integral to the functioning of the system and are not considered wasteful losses.

Water Exposure and Pumping Regime

The design and operation of iAVs contribute to its efficient water use. Key factors include:

  • Water Soaking: Once water soaks into the sand beds, the surface quickly dries out, reducing the amount of water exposed to evaporation-inducing elements.
  • Intermittent Pumping: The intermittent pumping regime in iAVs means that water is in play for less time compared to other systems, further limiting evaporative loss.

Absence of Filters

Unlike many other aquaculture systems, iAVs do not require filters beyond the sand beds. This eliminates the need for filter cleaning, a process that often leads to additional water loss in other systems.

 

3.8 CHAPTER SUMMARY 

 

  • Water is the lifeblood of an iAVs. It is the medium through which plants receive their nutrients and the fish receive their oxygen. It is beneficial to understand water quality and basic water chemistry in order to properly manage an iAVs. 
  • There are five key water quality parameters for iAVs:dissolved oxygen (DO), pH, water temperature, total nitrogen concentrations and hardness (KH). Knowing the effects of each parameter on fish, plants and bacteria is crucial.
  • Compromises are made for some water quality parameters to meet the needs of each organism in iAVs. 
  • The target ranges for each parameter are as follows:

pH 6.4 (+/- .04 )

Water temperature 18–30 °C 

DO 5–8 mg/litre  DOES THIS MATTER IN IAVS

Ammonia 0 mg/litre 

Nitrite 0 mg/litre 

Nitrate 5–150 mg/litre 

KH 60–140 mg/litre 

  • There are simple ways to adjust pH. Bases, and less often acids, can be added in small amounts to the water in order to increase or lower the pH, respectively. Acids and bases should always be added slowly, deliberately and carefully. 
  • Some aspects of the water quality and water chemistry knowledge needed THIS GOES AGAINST THE LO TECH PHILOSOPHY OF IAVS  for iAVs can be complicated, in particular the relationship between pH and hardness, but basic water tests are used to simplify water quality management.
  • Water testing is essential to maintaining good water quality in the system. IS IT THOUGH? Test and record the following water quality parameters each week: pH, water temperature, nitrate and carbonate hardness. Ammonia and nitrite tests should be used, especially at system start-up and if abnormal fish mortality raises toxicity concerns. 

 

4. Design of iAVs

 

This chapter discusses the theory and design of iAVs. 

 

This section delves into the principles and construction of iAVs, highlighting the numerous design elements that need to be considered due to their influence on the iAVs ecosystem. The objective of this section is to explain these elements in a comprehensible manner and to offer an in-depth understanding of each component within an iAVs.

 

The first part of the chapter (Section 4.1) talks about what you need to think about when choosing a place for your iAVs. This includes things like how much sun the area gets, how exposed it is to wind and rain, and what the average temperature is.

 

The second part of the chapter (Section 4.2) goes over the basic parts you need for an iAVs. This includes the fish tank, the water, and the plumbing materials that help move the water around the system.

 

This chapter is intended only to explain the essential unit components. NEED TO REPLACE THE PICTURE AS THE SUMP (SHOWN) IS NOT ESSENTIAL

 

For a more comprehensive understanding of the dimensions and design proportions of various unit components, refer to Chapter 8. It offers in-depth information, diagrams, and design blueprints necessary for the actual design and construction of a small-scale iAVs. 

 

Appendix 8 provides a comprehensive, step-by-step manual for constructing a small-scale model of the three methods discussed in this chapter, utilizing materials that are readily accessible. CHECK AND MAKE SURE IT DOES! AND CONFIRM ITS NOT DUPLICATED ELSEWHERE

 

REPLACE THE IMAGE BELOW

 

4.1 SITE SELECTION 

 

Choosing the appropriate location is a crucial step that needs to be taken into account before setting up an iAVs.

 

This part mainly pertains to an iAVs constructed outdoors, however, it is always advisable to incorporate a greenhouse or shading structure. It’s also essential to bear in mind that certain elements of the system, particularly the water and sand, are hefty and challenging to transport, thus it’s beneficial to construct the system at its permanent site.

 

The selected location should be on a steady and even surface, in a region that is safeguarded from extreme weather conditions yet receives plenty of sunlight.

4.1.1 Stability 

 

Ensure that you select a location that is stable and level. 

 

Several key elements of an iAVs are hefty, which could potentially cause the system to sink into the ground if it were to have legs. If not properly managed, this could result in disrupted water flow, flooding, or even a disastrous collapse. It’s crucial to select the most level and firm ground possible. 

 

Concrete slabs are appropriate, but they prevent any components from being buried, which could create tripping hazards. If the system is constructed on soil, it’s beneficial to level the soil and lay down material to control weed growth.

 

Moreover, for systems that do have legs, placing concrete or cement blocks under the legs of the grow beds can enhance stability. Stone chips are frequently utilized to level and stabilize soil-based locations.

 

However, the low-tech version, which is built directly on the ground and doesn’t have legs, is the ideal model for conserving labour and resources.

 

4.1.2 Exposure to wind, rain and snow

 

Severe weather conditions can put plants under stress and ruin structures.

 

Dominant winds can significantly hinder plant growth and inflict damage to stems and reproductive components.

 

Moreover, heavy rainfall can injure the plants and damage exposed electrical outlets. Excessive rain can dilute the nutrient-dense water, and potentially flood the system if it lacks an overflow mechanism.

 

If the area is prone to heavy rainfall, it might be beneficial to shield the system with a plastic-lined hoop house, though this may not be required in every location.

 

4.1.3 Exposure to sunlight and shade 

 

Sunlight is critical for plants, and as such, the plants need to receive the optimum amount of sunlight during the day. Most of the common plants grow well in full sun conditions; however, if the sunlight is too intense, a simple shade structure can be installed over the grow beds. 

 

Some light sensitive plants, including lettuce, salad greens and some cabbages, will bolt in too much sun, go to seed and become bitter and unpalatable. 

 

Other tropical plants adapted to the jungle floor such as turmeric and certain ornamentals can exhibit leaf burn when exposed to excessive sun, and they do better with some shade. On the other hand, with insufficient sunlight, some plants can have slow growth rates. 

 

This situation can be avoided by placing the iAVs in a sunny location. If a shady area is the only location available, it is recommended that shade-tolerant species be planted. Systems should be designed to take advantage of the sun travelling from east to west through the sky. 

 

Generally, the grow beds should be spatially arranged such that the longest side is on a north–south axis. This makes the most efficient use of the sun during the day. 

 

Alternatively, if less light is preferable, orient the beds, pipes and canals following the east–west axis. Also consider where and when there are shadows that cross the chosen site. 

 

Be careful in the arrangement of plants such that they do not inadvertently shade one another. However, it is possible to use tall, sun-loving plants to shade low, light-sensitive plants from intense afternoon sun by placing the tall plants to the west or by alternating the two in a scattered distribution.

 

Unlike the plants, the fish do not need direct sunlight. In fact, it is important for the fish tanks to be in the shade. 

 

Normally, the fish tanks are covered with a removable shading material that is placed on top of the tank. However, where possible, it is better to isolate the fish tanks using a separate shading structure. This will prevent algae growth (see Chapter 3) and will help to maintain a stable water temperature during the day. 

 

It is also worth preventing leaves and organic debris from entering the fish tanks, as the decaying leaf matter can stain the water, affect water chemistry and clog pipes. Either locate the system away from overhanging vegetation or keep the tank covered with a screen. 

 

Moreover, fish tanks are vulnerable to predators. Using shade netting, tarps or other screening over the fish tanks will prevent all of these threats. 

 

4.1.4 Utilities, fences and ease of access 

 

When choosing a location, the accessibility of utilities is a crucial factor to consider.

Electrical outlets are required for water and air pumps. These outlets should be protected from water and fitted with a residual-current device (RCD) to minimize the risk of electric shock; RCD adapters can be obtained from regular hardware stores.

 

It’s worth mentioning that ‘low-tech’ versions of iAVs can operate manually, without the need for electricity.

 

Furthermore, the water source, whether it’s municipal water or rain collection units, should be readily available. The system should be situated in a place that allows easy daily access, as regular checks and daily feeding are necessary.

 

Lastly, consider whether it’s essential to enclose the entire area with a fence. Fences are sometimes needed to deter theft and vandalism, keep out animal pests, and comply with certain food safety regulations.

 

4.1.5 Special considerations: rooftop iAVs

 

Flat rooftops frequently make ideal locations for iAVs as they are level, steady, receive ample sunlight, and are typically not already utilized for farming (Figures 4.16). REPLACE PICTURE

 

However, when constructing a system on a rooftop, it’s vital to take into account the system’s weight and whether the roof can bear it. It’s crucial to seek advice from an architect or civil engineer prior to building a rooftop system.

 

Furthermore, ensure that materials can be safely and efficiently transported to the rooftop location.

 

4.1.6 Greenhouses and shading net structures 

 

While greenhouses aren’t necessary for small-scale iAVs, they can be beneficial in prolonging the growing season in certain areas. This is especially true in temperate and other cooler regions globally, as greenhouses can help maintain warm water temperatures during colder months, enabling year-round production.

 

A greenhouse is a structure made of metal, wood, or plastic, covered with transparent nylon, plastic, or glass. Its purpose is to let sunlight (solar radiation) in and trap it, thereby heating the air inside. 

 

As the sun sets, the heat is kept inside by the roof and walls, ensuring a warmer and more stable temperature over a 24-hour period.

 

Greenhouses offer protection from wind, snow, and heavy rain. They extend the growing season by retaining solar heat and can also be heated internally. They can deter animals and pests and provide some security against theft. Greenhouses are comfortable to work in during colder seasons, protecting the grower from the weather. The frames can support climbing plants or hang shade material.

 

These greenhouse benefits can lead to increased productivity and an extended cropping season. However, these advantages must be weighed against the downsides. The initial investment for a greenhouse can be high, depending on the level of technology and sophistication desired.

 

Greenhouses also incur additional operating costs as fans are needed to circulate air to prevent overheating and excessive humidity. Some diseases and insect pests are more prevalent in greenhouses and must be managed accordingly (e.g., using insect nets on doors and windows), although the enclosed environment can facilitate certain pest controls.

 

In some tropical regions, net houses are more suitable than traditional greenhouses covered with polyethylene plastic or glass (Figure 4.21). This is due to the hot climates in the tropics or subtropics, which necessitate better ventilation to avoid high temperatures and humidity.

 

Net houses are structures built over the grow beds, featuring mesh netting on all four sides and a plastic roof on top. The plastic roof is crucial to prevent rain from getting in, especially in regions with heavy rainy seasons, as the units could overflow within a few days.

 

Net houses are utilized to mitigate the risk of numerous harmful pests associated with tropical climates, as well as birds and larger animals. The optimal mesh size for the four walls is dependent on the local pests.

 

For larger insects, a mesh size of 0.5 mm is suitable. For smaller ones, often carriers of viral diseases, a denser mesh (i.e., mesh 50) should be used.

 

Net houses can also provide some shade if the sunlight is overly intense. Typical shade materials range from 25 to 60 percent sunblock.

 

4.2 ESSENTIAL COMPONENTS OF AN AQUAPONIC UNIT 

 

Every iAVs has several common and essential components. These include: a fish tank, and a biofilter. Each system uses energy MANUAL OR OTHERWISE  to circulate water through pipes and plumbing 

 

while aerating the water. As introduced above, there are three main designs of the plant growing areas including: grow beds, grow pipes and grow canals. AT SOME POINT FURROWS AND RIDGES NEED TO BE ADDED TO THIS DOCUMENT AS AN ESSENTIAL COMPONENT IN THE BIOFILTER SECTION

 

 This section discusses the mandatory components, including the fish tank, biofilter, plumbing and pumps.NEED TO REWRITE TO INCLUDE POSSIBLE MANUAL OPERATIONS AND WITHOUT PIPES 

 

The following sections are dedicated to the separate hydroponic techniques, and a comparison is made to determine the most appropriate combination of techniques for different circumstance.

 

4.2.1 Fish tank 

 

Fish tanks are a vital part of every unit, and they can make up to 20 percent of the total expense of an iAVs.

 

Fish need specific conditions to live and prosper, so the selection of the fish tank should be done with care. Several key factors to consider include the shape, material, and colour of the tank. 

 

It’s also important to mention the significance of solids removal. Removing solids is crucial for ensuring that plants have sufficient nutrients and for maintaining fish health to optimize growth.

 

Tank shape 

 

REWRITE THIS TO MENTION A CATENARY SHAPED TANK AND ETC.. Although any shape of fish tank will work, round tanks with flat bottoms are recommended. The round shape allows water to circulate uniformly and transports solid wastes towards the centre of the tank by centripetal force. REWRITE THIS SO THE FOCUS IS MORE ON THE SHAPE OF THE BOTTOM OF THE TANK

 

Square tanks with flat bottoms are perfectly acceptable, but require more active solid-waste removal. Tank shape greatly affects water circulation, and it is quite risky REWRITE THIS to have a tank with poor circulation. 

 

Artistically shaped tanks with non-geometric shapes with many curves and bends can create dead spots in the water with no circulation. These areas can gather wastes and create anoxic, dangerous conditions for the fish. If an odd-shaped tank is to be used, it may be necessary to add water pumps or air pumps to ensure proper circulation and remove the solids. 

 

It is important to choose a tank to fit the characteristics of the aquatic species reared because many species of bottom dwelling fish show better growth and less stress with adequate horizontal space.

 

Material 

 

Either strong inert plastic or fibreglass is recommended because of their durability and long life span. Metal is not possible because of rust. 

 

Plastic and fibreglass are convenient to install (also for plumbing) and are fairly light and maneuverable. 

 

Animal-watering troughs are commonly used, as they tend to be cheap. If using plastic containers, make sure that they are UV-resistant because direct sunlight can destroy plastic.

 

In general, low-density polyethylene (LDPE) tanks are preferable because of their high resistance and food-grade characteristics. Indeed, LDPE is the most commonly used material for water storage tanks for civil uses. 

 

Another option is an in-ground pond. Natural ponds are very difficult to manage for iAVs because the natural biological processes, already occurring within the substrate and mud at the bottom, can be hard to manipulate and the nutrients are often already used by aquatic plants. REWRITE THIS BECAUSE THE IAVS DESIGN WORKS GREAT WITH PONDS – PERHAPS AND ADD-ON SECTION FOR THIS PDF 

 

Cement or plastic-lined ponds are much more acceptable, and can be an inexpensive option. WHAT ADD SECTION – OR LINK TO SECTION – ABOUT CONCRETE LEACHING AND CHANGING THE PH

 

 In-ground ponds can make plumbing operations difficult, and the plumbing design should be carefully considered before embarking on this option. MENTION THE BENEFITS OF AN IN-GROUND TANK 

 

One of the simplest fish tanks is a hole dug in the ground, lined with bricks or cinderblocks, and then lined with a waterproof liner such as polyethylene plastic. 

 

Other options include secondhand containers, such as barrels or intermediate bulk containers (IBCs). It is very important to make sure the container has not been used previously to store toxic material. 

 

Contaminants, such as solvent-borne chemicals, will have penetrated into the porous plastic itself and are impossible to remove with washing. Thus, choose used containers carefully, and know the seller if possible.

 

Colour 

 

White or other light colours are strongly advised as they allow easier viewing of the fish in order to easily check behaviour and the amount of waste settled at the bottom of the tank (Figures 4.22). 

 

White tanks will also reflect sunlight and keep the water cool. 

 

Alternatively, the outside of darker coloured tanks can be painted white. In very hot or cold areas, it may be necessary to further thermally insulate the tanks.

 

Covers and shading 

 

Every fish tank should have a cover. These shade covers help inhibit the growth of algae.

 

Moreover, the covers stop fish from leaping out, keep leaves and debris from getting in, and protect the fish from predators like cats and birds.

 

Frequently, agricultural shading nets are utilized. The shade cloth can be affixed to a basic wooden frame to add weight and make the cover easy to remove.

 

Failsafe and redundancy 

 

Do not let the fish tank lose its water; fish will die if the fish tank accidentally drains. Although some accidents are unavoidable, most catastrophic fish kills are the result of human error. Ensure that there is no way for the tank to drain without a deliberate choice by the operator. 

 

If the water pump is located in the fish tank, be sure to lift the pump off the bottom so that the tank can never be pumped dry. Use a standpipe inside the tank to guarantee a minimum water level. This is discussed further in Section 4.2.6. REWRITE AND ADD INFO ABOUT FLOAT SWITCHES AS WELL AS ENSURING PROPER DRAINAGE AND PROPER FLOW RATES

 

4.2.2 Filtration – mechanical and biological 

 

REPLACE THIS SECTION OTHERWISE EVERY CHAPTER NEEDS TO BE RENUMBERED IF THIS SECTION IS DELETED!!!PERHAPS REWRITE IT SHORT AND SWEET TO SAY THAT THE MECHANICAL FILTRATION IS DONE IN THE BIOFILTER (SANDBED) 

 

Mechanical filtration For RASs, mechanical filtration is arguably the most important aspect of the design. Mechanical filtration is the separation and removal of solid and suspended fish waste from fish tanks. 

 

It is essential to remove these wastes for the health of the system, because harmful gases are released by anaerobic bacteria if solid waste is left to decompose inside the fish tanks. 

 

Mechanical separators (clarifiers)

SKIPPED – 

 

Biofiltration

SKIPPED – 

 

A required component for the biofilter is aeration. Nitrifying bacteria need adequate access to oxygen in order to oxidize the ammonia.  

 

Mineralization 

 

Mineralization refers to the way that solid wastes are processed and metabolized by bacteria into nutrients for plants. Solid wastes that are trapped by the mechanical filter contain nutrients; although processing these wastes is different from biofiltration and requires separate consideration. Retaining the solids within the overall system will add more nutrients back to the plants. Any waste that remains on the mechanical filters, within the biofilters or in the grow beds is subjected to some mineralization. Leaving the waste in place for longer allows more mineralization; longer residence time of the waste in the filters will lead to more mineralization and more nutrients being retained in the system. However, this same solid waste, if not properly managed and mineralized, will block water flow, consume oxygen and lead to anoxic conditions, which in turn lead to dangerous hydrogen sulphide gas production and denitrification. Some large systems therefore deliberately leave the solid waste within the filters, ensuring adequate water flow and oxygenation, so that a maximum of the nutrients is released. THIS WHOLE SECTION NEEDS TO BE REWRITTEN AND IT SHOULD NOT BE IN THE FISH TANK SECTION – IT WILL BE ADDED TO THE BIOFILTER SECTION

 

Using a media bed for a combination of mechanical and biological filtration

SKIPPED – 

REPLACE THIS WITH A SECTION THAT EXPLAINS THE SAND BEDS ARE THE COMBINATION OF…

 

4.2.3 Hydroponic components – media beds, NFT, DWC

SKIPPED – 

 

4.2.4 Water movement

SKIPPED – 

 There are three commonly used methods of moving water through a system: submersible impeller pumps, airlifts and human power. 

 

Submersible impeller water pump 

 

Most commonly, an impeller-type submersible water pump is used and this type of pump is recommended for small scale units (Figure 4.41). REPLACE IMAGE

 

External pumps could be used, but they require further plumbing and are more appropriate for larger designs. 

 

High-quality water pumps should preferably be used in order to guarantee a long life span and energy efficiency. Top-quality pumps will maintain their pumping capacity and efficiency for least 1–2 years, with an overall life span of 3–5 years, whereas inferior products will lose their pumping power in a shorter time, leading to significantly reduced water flows. 

 

Regarding flow rate, the small-scale units described in this publication need a flow rate of 2 000 litres/h at a head height of 1.5 meters; a submersible pump of this capacity would consume 25–50 W/h. REPLACE

 

A helpful approximation to calculate energy efficiency for submersible pumps is that a pump can move 40 litres of water per hour for every watt per hour consumed, although some models claim twice this efficiency. CHECK THIS

 

When designing the plumbing for the pump, it is important to realize that pumping power is reduced at every pipe fitting; up to 5 percent of the total flow rate can be lost at each pipe connection when water is forced through. Thus, use the minimal number of connections between the pump and the fish tanks. 

 

It is also important to note that the smaller the diameter of the pipes, the larger the water flow loss. A 30 mm pipe has twice the flow of a 20 mm pipe even if served from pumps with same capacity. In addition, a larger pipe does not require any maintenance to remove the buildup of solids accumulating inside. 

 

In practical terms, this results in significant savings on electricity and operating costs. Submersible water pumps will break if they are run without water; never run a pump dry. 

 

Airlift 

 

Airlifts are another technique of lifting water (Figure  4.42). They use an air pump rather a water pump. Air is forced to the bottom of a pipe within the fish tank, bubbles form and burst, and during their rise to the surface the bubbles transport water with them. 

 

One benefit is that airlifts can be more electrically efficient, but only at small head heights (30–40  cm). Air lifts gain power in deeper tanks, and are best at a depth greater than one metre. An added value is that airlifts do not clog the way that submersible impeller-type pumps do. 

 

In addition, water is also oxygenated through the vertical movement operated by the air bubbles. However, the volume of air pumped should be adequate to move the water along the pipe. 

 

Air pumps generally have a longer life than submersible water pumps. The main benefit comes from an economy of scale – a single air pump can be purchased for both aeration and water circulation, which reduces the capital investment in a second pump. 

 

Human power 

 

Some iAVs have been designed to use human power to move water (Figure 4.43). Water can be lifted in buckets or by using pulleys, modified bicycles, calabash or other means. 

 

4.2.5 Aeration 

 

ADD TO THIS SECTION THEY ARE OPTIONAL AND WHY BUT ALSO HOW THIS PERTAINS TO FISH NOT USED IN THE RESEARCH 

 

Air pumps introduce air into the water via air pipes and air stones situated inside the water tanks, which enhances the Dissolved Oxygen (DO) levels in the water (Figure 4.44).

 

Air stones are positioned at the end of the air line and function to disperse the air into tinier bubbles (Figure 4.45).

 

Smaller bubbles have a larger surface area, and thus, they infuse oxygen into the water more effectively than larger bubbles; this increases the efficiency of the aeration system and helps to reduce costs.

 

It’s advisable to use high-quality air stones to achieve the smallest air bubbles.

 

Biofouling is inevitable, and air stones should be routinely cleaned, initially with a chlorine solution to eliminate bacterial deposits, and then, if required, with a very mild acid to remove mineralization, or replaced when the bubble flow is uneven.

 

If feasible, it’s better to use an AC/DC combination air pump to prepare for potential power outages. This is because, during a power failure, the charged DC batteries can continue to operate even when disconnected from AC power.

Sizing aeration systems 

 

TOTAL REWRITE For small-scale units, with about 1000 litre fish tanks, it is recommended that at least two air lines, also called injectors, with air stones should be placed in the fish tank, and one injector in the biofilter container. To understand the volume of air entering the system, it is worth measuring the flow rate. To do this, simply invert a volumetric measuring device (a 2 litre bottle, measuring cup, graduated beaker) in the fish tank. With the help of an assistant, begin a stopwatch at the same time as the bubbling air stone is inserted into the measuring device. Stop the stopwatch when the container is full of air. Then, determine the flow rate in litres per minute using a ratio. The target for systems described here is 4–8 litres/ min for all of the air stones combined. It is always better to have extra DO rather than not enough. Try to place air stones so that they do not re-suspend settling solids, thus preventing their removal through the centre drain.

 

Venturi siphons

SKIPPED – REPLACE IT WITH A SECTION ABOUT CASCADE AERATORS AND UPDATE THE CONTENTS PAGE

 

Cascade Aerators

When a location lacks alternatives – that is, there’s no electrical power for devices like blowers, compressors, or pumps – cascade aerators can enhance the Dissolved Oxygen (DO) levels in an aquaculture body of water. The central concept is to utilize gravity to fragment a water flow into the maximum number of droplets possible, repeatedly. This significantly expands the surface area that directly interacts with the atmosphere, which contains 21% Oxygen.

 There is nearly an infinite number of ways to accomplish this.  Below are but a few examples.

 

In addition to aerating the biofilter drainage following irrigation events, it would also be possible to aerate the grow-out tank/pool volume without the water passing thru the sand (any hour of the day/night if desired).  Pour/move water onto the top of the cascade directly by whatever means is available.

Also, do try to shade the cascade from direct sunlight.  This reduces evaporation ‘loss’ and heat gained by the water.

Further, even with access to electrical energy for aeration, adding a cascade can increase DO saturation and/or reduce your energy bill.

Cone Aerators   

Cone aerators are used primarily to oxidize iron and manganese from the ferrous state to the ferric state prior to filtration. The design of the aerator is similar to the cascade type, with the water being pumped to the top of the cones and then being allowed to cascade down through the aerator.

Slat and Coke Aerators  

The slat and coke trays are similar to the cascade and cone types. They usually consist of three-to-five stacked trays, which have spaced wooden slats in them. The trays are filled with fist-sized pieces of coke, rock, ceramic balls, limestone, or other materials. The primary purpose of the materials is to provide additional surface contact area between the air and water.”

Open channel Low-Profile Cascade Aerator 

Stepped Cascade, Cone and Stack types mentioned here

Pooled Stepped Cascade design parameters (technical)  True, this technique is ‘powered’, but some of the same principles apply.

4.2.6 Sump tank 

 

REWRITE THIS AS A SUMP IS NOT THE IDEAL, PERHAPS LINK IT TO THE DESIGN SECTION ABOUT VARIOUS BUILD MODELS 

 

The sump tank is a water collection tank at the lowest point in the system; water always runs downhill to the sump (Figure 4.47). 

 

Although helpful, it is not an essential system component, and many designs do not employ an external sump tank. However, for larger units it is very useful to have a sump.

 

4.2.7 Plumbing materials 

 

TOTAL REWRITE NEEDED HERE Every system requires a selection of PVC pipe, PVC connections and fittings, hoses and tubes (Figure  4.48). These provide the channels for water to flow into each component. Bulkhead valves, Uniseals® (hereafter uniseal), silicone sealant and Teflon tape are also needed. The PVC components are connected together in a permanent way using PVC cement, although silicone sealant can be temporarily used if the plumbing is not permanent and the joints are not under high water pressure. In addition, some general tools are needed such as hammers, drills, hand saws, electric saws, measuring tapes, pliers, channel-locking pliers, screwdrivers, levels, etc. One special tool is a hole-saw and/ or spade bit, which are used in an electric drill to make holes up to 8 cm, necessary for inserting the pipes into the fish tanks and filters, as well as for making holes in the PVC or polystyrene grow beds in NFT and DWC systems. Appendix 8 contains a detailed list of materials needed for each unit described in this publication. Make sure that the pipes and plumbing used in the system have never previously been used to hold toxic substances. It is also important that the plumbing used is of food-grade quality to prevent possible leeching of chemicals into the system water. It is also important to use pipes that are black and/or non-transparent to light, which will stop algae from growing

 

4.2.8 Water testing kits 

 

Simple water tests are an easy way to determine water quality.

 

 Colour-coded freshwater test kits are readily available, fairly economical and easy to use, and thus these are recommended. CHECK TO SEE IF THIS IS ACCURATE These can be purchased in aquarium stores or online. These kits include tests for pH, ammonia, nitrite, nitrate, GH and KH (Figure  4.49). Be sure that the manufacturers are reliable and that the expiration date is still valid. 

 

Other methods include digital meters or test strips. If using digital meters for pH or nitrate, be sure to calibrate the units according to the manufacturer’s directions. 

 

A thermometer is necessary to measure water temperature. 

 

In addition, if there is risk of saltwater in the source water, a cheap hydrometer, or a more accurate but more expensive refractometer, is worthwhile. 

 

More details on the use of colourimetric test kits are included in Section 3.3.6.

 

4.3 THE MEDIA BED TECHNIQUE

 

In media bed units, the medium is used to support the roots of the plants and also the same medium functions as a filter, both mechanical and biological.

 

MOVE SAND TO THIS SECTION 

 

4.3.1 Water flow dynamics 

 

THIS SECTION NEEDS TO BE CLEANED UP AND REWRITTEN WITH LNKS TO IRRIGATION, FURROWS, SATURATION AND DRAINAGE

 

Figure  4.50 shows the main components of an iAVs using media beds, including the fish tank, the media beds, the sump tank and water pump, as well as concrete blocks for support. It is easiest to understand by following the water flow through the system.

 

Water flows from the fish tank into the media beds. These media beds are full coarse sand that serves as both the mechanical and biological filter and location for mineralization. AS MENTIONED IN SECTION ??

 

These beds both host the colony of nitrifying soil bacteria and provide the place for the plants to grow. On exiting the media beds, the water travels down,by gravity back to the fish tank completing the cycle. At this point, the water is free of solid and dissolved wastes. 

 

Media beds are designed to flood-and-drain, which means that the sand is saturated and then completely drains. This adds oxygen to the plant roots and aids in the biofiltration of the ammonia. REWRITE

 

4.3.2 Biofilter Construction 

ADD IN SECTIONS FROM THE COURSE

 

Materials 

 

Media beds can be made from plastic, fibreglass or a wooden frame with water-tight rubber or polyethylene sheeting on the base and inside the walls. 

 

The most popular “do-it-yourself” (DIY) media beds are made from plastic containers, modified IBCs or even old bathtubs. It is possible to use all of the above as beds and other kinds of tanks so long as they meet these following requirements: 

 

  • strong enough to hold water and sand without breaking; 
  • able to withstand difficult weather conditions; 
  • Made of food grade material that is safe for the fish, plants and bacteria;
  •  can be easily connected to other unit components through simple plumbing parts and 
  • can be placed in proximity to the other unit component

 

Shape 

 

The standard shape for media beds is a rectangle, with a width of about 1.2m and a length of 1–3 m. Larger beds can be used / manufactured, but they require additional support (i.e. concrete blocks) in order to hold their weight. 

 

The beds should not be so wide that the farmer/ operator is unable to reach across, at least half-way.

 

Depth 

 

REWRITE TO MENTION THE RESEARCH AND ALSO ABOU SURFACE AREA, LINK TO OTHER SECTION IF NEEDED 

 

Media bed depth is important because it controls the amount of root space volume in the unit which determines the types of vegetables that can be grown. If growing large fruiting vegetables such as tomatoes, okra or cabbage, the media bed should have a depth of 30 cm, without which the larger vegetables would not have sufficient root space, would experience root matting and nutrient deficiencies, and would probably topple over. 

 

Small leafy green vegetables only require 15–20 cm of media depth, making them a good choice if the media bed size is limited. Even so, some experiments have shown that even the larger crops can be grown in shallow beds if the nutrient concentrations are sufficient.

 

4.3.3 SAND Choice of medium

 

The medium needs to have adequate surface area while remaining permeable for water and air, thus allowing the bacteria to grow, the water to flow and the plants roots to breathe. REWRITE

 

The medium must be inert, not dusty, and non-toxic, and it must have a neutral pH so as not to affect the water quality.

 

These essential criteria are listed below:

 

  • Large surface area for bacterial growth
  • neutral pH and inert
  • Good drainage properties
  • Easy to work with
  • Sufficient space for air and water to flow within the medium

 

ADD A SECTION HERE – IF NEEDED – TO ADD MORE INFO ABOUT SAND

 

Displacement of water by media 

 

IS THIS SECTION NEEDED? Depending on the medium, it will occupy roughly 30–60 percent of the total media bed volume. This percentage will help decide on the sump tank size for each unit, because the sump tank, at the very least, will need to hold the total water volume contained in all the media beds. Sump tanks should be slightly oversized to ensure that there is always adequate water for the pump to run without ever running dry.

 

 For example, for a media bed of 1  000  litres (dimensions 2  m long × 2  m wide ×  0.25  m medium depth), the growing medium will displace 300–600  litres of this space, and therefore the water volume of the media bed would be 400–700 litres.

 

 It is recommended that the sump volume be at least 70 percent of the total media bed volume. For this example, the sump tank should be approximately 700 litres.

 

4.3.4 Filtration 

 

The biofilter serves as both mechanical and biological filtration and plant growing area.

 

 In addition, the biofilter provides a place for mineralization to occur. 

 

However, at high stocking densities (>15 kg/m3 ), the mechanical filtration can be overwhelmed and can face the risk of having the media clogged and producing dangerous anaerobic spots. 

 

Mechanical filter 

 

The biofilter functions as a large physical filter, capturing and containing the solid and suspended fish waste and other floating organic debris.

 

 The effectiveness of this filter will depend on the particle size of the medium because smaller particles are more densely packed and capture more solids. Moreover, a high water flow rate can force particles through the media bed and escape the filter. 

 

Over time, the captured solid wastes will break down and be mineralized. A properly balanced system will process all the incoming solid wastes. When biofilters are improperly sized for the stocking density, the media bed can become clogged with solids. EXPLAIN HOW THIS CAN EASILY BE FIXED 

 

This indicates a mistake in the original design when the feed rate ratio was used to balance the system. 

 

This situation leads to beds clogged with solid waste, poor water circulation, anoxic areas and dangerous conditions. 

 

To avoid this situation be sure that the original design considered the stocking density, feeding regime, and used the feed rate ratio to calculate the required area of the media bed.

 

Biological filtration 

SKIPPED 

 

Mineralization 

RELINK OR MOVE OTHER MENTIONS OF THIS BACK TO THIS SECTION

 

Over time, the solid and suspended fish waste and all other debris are slowly broken down by biological and physical processes into simple nutrients in the form of simple molecules and ions that the plants can easily absorb.

 

This process is described in more detail in Section 4.2.2 and Chapter 5. CHECK LINKS

 

The Biological Facilitation of Mineralization

iAVs utilizes a sand biofilter to facilitate a process often referred to as ‘mineralization’. This process is not merely a chemical reaction, but a biologically mediated transformation that is more effective, complete, and organic in nature.

The Biofilter and Mineralization

In the context of iAVs, the term ‘biofilter’ signifies the biologically mediated chemical processes that occur within the system. The ‘mineralization’ that takes place in the sand biofilter of an iAVs system is a complex process involving redox reactions, which are a type of chemical reaction where the oxidation states of substrates change.

Components of the iAVs System

The iAVs system is a combination of several key components:

  • Sand: The medium in which the biofilter operates.
  • Microbial Communities: The biological component that facilitates the chemical transformations.
  • Organic Compounds: The substrate that includes complex biomolecules.
  • Molecular Oxygen: The energy source for the system.
  • Water: The solvent that enables the reactions.

When these components interact, they create a system that functions similarly to soil, but with enhanced capabilities for mineralization.

 

4.3.5 The three zones of media beds – characteristics and processes 

 

THIS MAY NEED A TOTAL REWRITE 

 

The nature of a flood-and-drain media bed creates three separate zones that can be considered microecosystems, which are differentiated by their water and oxygen content. Each zone hosts a diverse group of bacteria, fungi, micro-organisms, worms, insects and crustaceans. 

 

One of the most important is the nitrifying bacteria used for biofiltration, but there are many other species that all have a role in the breaking down of fish wastes. 

 

It is not essential to be aware of all these organisms, but this section briefly outlines the differences between these three zones and some of the ecological processes occurring in each.

 

Dry zone 

 

THIS SECTION SEEMS NOT NEEDED UNLESS IT IS REWRITTEN TO DESCRIBE THE DIFFERENT SECTIONS OF THE RIDGES AND FURROWS 

 

The top 2–5 cm of the ridges is the dry zone. This zone functions as a light barrier, preventing the light from hitting the water directly which can lead to algal growth. It also prevents the growth of fungus and harmful bacteria at the base of the plant stem, which can cause collar rot and other plant diseases. 

 

Another reason to have a dry zone is to minimize evaporation from beds by covering the wet zone from direct light. Moreover, beneficial bacteria are sensitive to direct sunlight. 

 

Dry/wet zone 

 

This is the zone that has both moisture and high gas exchange. 

 

In flood-and-drain techniques (discussed below) this is the 10–20  cm space where the media bed intermittingly floods and drains (Figure 4.57). Most of the biological activity will occur in this zone. 

 

The root development, the beneficial bacteria colonies and beneficial micro-organisms are active in this zone. The plants and the animals receive their water, nutrients and oxygen because of the interface between air and water. 

 

Wet zone

SKIPPED

 

4.3.6 Irrigating media beds 

 

REPLACE THIS SECTION WITH THE ‘INTERMITTENT IRRIGATION REGIME’ There are different techniques to deliver water to media beds, each can be relevant depending on the local availability of materials, the degree of technology desired or the experience of the operators. 

 

A method called flood-and-drain, also known as ebb-and-flow, is used where the system of plumbing causes the media beds to flood with water from the fish tank and then drain back in the fish/sump tank. This is accomplished through timed pumping. This alternation between flooding and draining ensures that the plants have both fresh nutrients and adequate air flow in the root zone. 

 

This thereby replenishes the oxygen levels for plants and bacteria. It also ensures that enough moisture is in the bed at all times so the bacteria can thrive in their optimum conditions. Usually, these systems go through the complete cycle 1–2 times every hour, but some successful systems only cycle 3–4 times per day. 

 

Bell siphon

SKIPPED

 

Timer mechanism 

 

REWRITE This method of flood-and-drain irrigation relies on a timer switch on the water pump to control the periodic flooding and draining (Figure 4.59). The benefit of this method is that there is no autosiphon. 

 

Water flow dynamics 

 

REWRITE THIS SO IT IS ABOUT THE FURROWS AND SATURATION Water flows into the grow bed, flooding the bed until the water reaches the top of the standpipe. The water then drains through this standpipe and down into the sump tank. The large standpipe is of sufficient diameter to drain all of the inflowing water; the top of the large standpipe is the deepest flood that the grow bed will experience. There is also a small inlet, 6–12 mm diameter, into this same standpipe located near the bottom. This small inlet is insufficient to drain all of the incoming water and, therefore, even as water enters the small inlet, the grow bed continues to flood until it reaches the top. At some point after the bed is full, the timer cuts the power to the water pump. Water in the media bed begins to flow out through the small inlet hole, continuing to drain the grow bed until the water reaches the level of the bottom hole. At this point, the power is returned to the water pump and the grow bed is refilled with fresh fish-tank water. It is very important that the water flowing into the media bed is greater than the water flowing through the small inlet in the standpipe so that the bed will fully flood again. The flooding and draining cycle length and the diameter of the dripping hole are determined by the size of the media bed and the incoming flow rate. To ensure adequate filtration, the entire fish tank volume should be pumped through the grow beds every hour. Finally, make sure to flush the beds out once every week by temporarily removing the standpipe and allowing the remaining water to drain. The materials involved for the timer method for the aquaponic designs included in this publication are as follows: a standpipe, 2.5 cm diameter, of a height of 23 cm that has a secondary dripping hole, 6–12 mm diameter, 2.5 cm above the bottom; a media guard, 11 cm diameter and 32 cm in height, encircling the standpipe to prevent media from clogging it; and a timer that controls the pump that is calibrated based on the flow rate of the pump and the drain rate of the standpipe.

 

THE SECTION BELOW MAY NEED TO REPLACE EVERYTHING ABOVE

 

Intermittent Irrigation in iAVs

SOME PARTS SEEM MISSING – LIKE ALTERNATING BEDS FOR EXAMPLE – CHECK THE IRRIGATION SECTION IN SOURCE

Intermittent irrigation is a crucial aspect of the Integrated AquaVegeculture System (iAVs). This method controls the water flow through the biofilter, ensuring optimal water and nutrient distribution for plant growth.

How Intermittent Irrigation Works

The intermittent irrigation process is typically controlled by a timer, which activates a water pump at predetermined intervals. The pump floods the furrows in the biofilter with nutrient-rich water until saturation is reached. Once the pump stops, the biofilter begins to drain, and the sand grains retain an adequate amount of water, neither too wet nor too dry.

 

This irrigation regime provides water and nutrients to the biofilter in a timely manner while maintaining the ideal moisture level for plant growth. The process is repeated every two hours during daylight hours, as photosynthesis cannot occur in darkness.

Irrigation Schedule

An example of an irrigation schedule is as follows:

  1. At 6:00 am, the pump is activated, and nutrient-rich water enters the biofilter, moving along the furrows and percolating down through the sand.
  2. Within seconds, the water begins to flow from the biofilter drain back into the water tank.
  3. After 15 minutes, the water reaches the top of the sand, and the pump stops.
  4. For the next 1 hour and 45 minutes, the biofilter drains.
  5. At 8:00 am, the pump starts again, runs for 15 minutes, and then stops.

This process is repeated every two hours during daylight hours.

Nighttime Rest

The biofilteris designed to rest overnight, meaning it is not irrigated by the pump during this time. This allows the biofilter to catch and store organic deposits, forming a detritus layer. CHECK THIS LINE The resting period also benefits the roots and rhizosphere processes, as well as the aerobic soil organisms, by providing abundant oxygen. HOW AND WHY?

Pumping Volume

It is recommended that the pumping event is equal to one-fourth of the total volume of the fish tank. This helps the biofilter effectively clean the water.

Fine-Tuning and Adaptations

Fine-tuning the irrigation volume and on/off cycle times depends on the drainage characteristics of the specific sand used in the system. Establishing baseline conditions and understanding the relationships involved in the system is crucial before making any adaptations.

 

4.4 NUTRIENT FILM TECHNIQUE (NFT)

SKIPPED – REPLACE AND UPDATE THE CONTENTS OTHERWISE EVERY OTHER SECTION NEEDS TO BE RENUMBERED!

 

4.4.1 Water flow dynamics 

 

TOTAL REWRITE The water flows by gravity from the fish tank, through the mechanical filter and into the combination biofilter/sump. From the sump, the water is pumped in two directions through a “Y” connector and valves. Some water is pumped directly back to the fish tank. The remaining water is pumped into a manifold that distributes the water equally through the NFT pipes. The water flows, again by gravity, down through the grow pipes where the plants are located. On exiting the grow pipes, the water is returned to the biofilter/sump, where again it is pumped either into the fish tank or grow pipes. The water that enters the fish tank causes the fish tank to overflow through the exit pipe and back into mechanical filter, thus completing the cycle. This design, as described in this publication, is called a “Figure 8” design because of the path of the water. This design ensures that filtered water enters both the fish tank and the grow pipes, while only using one pump. There is no need to place the sump lower than the rest of the unit, making this design possible to use on existing concrete floors or on rooftops. All components are at a comfortable working level for the farmer without stooping or using ladders. Moreover, the design fully utilizes the size of the IBC container to ensure adequate room for the fish. One drawback is that the combination sump/biofilter works to dilute the nutrient concentration of the water reaching the grow pipes, and at the same time, returns water to the fish before the water has been fully stripped of nutrients. However, the slight dilution is managed by controlling the bidirectional flow leaving the sump/biofilter and, overall, it has little effect on the efficacy of this system in light of the benefits provided. Generally, the pump returns 80 percent of the water to the fish tanks and the remaining 20 percent to the grow beds or canals, and this can be controlled with the valve.

 

4.4.2 Mechanical and biological filtration

SKIPPED

 

4.4.3 Nutrient film technique grow pipes, construction and planting

SKIPPED

 

4.5 DEEP WATER CULTURE TECHNIQUE

SKIPPED

 

4.5.1 Water flow dynamics

SKIPPED

 

4.5.2 Mechanical and biological filtration 

SKIPPED

 

4.5.3 DWC grow canals, construction and planting

SKIPPED

 

4.5.4 Special case DWC: low fish density, no filters

SKIPPED

 

Low stocking density unit management

REMOVE THIS OR MOVE IT? Previously, it has been suggested that the balance between fish and plants follows the feed rate ratio, which helps to calculate the amount of fish feed entering the system given a set growing area for the plants. These low stocking density units still follow the suggested daily feed rate ratio of 40–50 g/m2 , CONFIRM THISbut should be towards the lower end. 

 

A useful technique is to allow fish to feed for 15 minutes, 2 times per day, and then remove all uneaten food. Overfeeding will result in an accumulation of waste in the fish tanks and may lead to diseases and fish stress.

 

Advantages and disadvantages of low stocking density

THIS SECTION IS ABOUT DWC AND WILL BE REMOVED BUT PERHAPS ADD THIS INFO IN ANOTHER PLACE?? 

 

The major advantage is a simpler unit. This system is easier to construct and cheaper to begin, having lower capital costs. The fish are less stressed because they are grown in more spacious conditions. 

 

Overall, this technique can be very useful for initial projects with low capital. These systems can be very useful for growing high-value fish, such as ornamental fish, or specialty crops, such as medicinal herbs, where the lower production is compensated with higher value. 

 

4.6 COMPARING AQUAPONIC TECHNIQUES

SKIPPED

 

4.7 CHAPTER SUMMARY

NEEDS TO BE CHECKED AND REWRITTEN

  • The main factors when deciding where to place a unit are: stability of ground, access to sunlight and shading, exposure to wind and rain, availability of utilities, and availability of a greenhouse or shading structure.
  • The essential components for an iAVs are: the fish tank, the the grow beds, sand, and the water/air pumps.
  • The sand in an iAVs must inert, meaning there should be no chemical reaction when the sand comes in contact with water. It should also be free of silt or clay and must drain effectively.
  • High DO concentration is essential to secure good fish, plant, and bacteria growth. The ridges and furrows provide an interface between the wet zone and dry zone that provides a high availability of atmospheric oxygen. ????

 

5. Bacteria

Bacteria are a crucial and pivotal aspect of iAVs, serving as the bridge that connects the fish waste to the plant fertilizer.

 

 This biological engine removes toxic wastes by transforming them into accessible plant nutrients. Chapter 2 discussed the nitrogen cycle, especially the critical role of nitrifying SOIL? bacteria, and outlined the essential parameters for maintaining a healthy colony. Chapter 4 discussed the aspects of biofilter materials that host these same bacteria. CHECK CHAPTER 4 AND UPDATE THIS IF IT DISCUSSES SAND/BACTERIA 

 

This brief chapter serves as a review of the bacteria, including details of the important bacterial groups. Heterotrophic bacterial activity is more fully discussed in terms of its role in the mineralization of solid fish waste. Unwanted bacteria are discussed, including: denitrifying bacteria, sulphate-reducing bacteria and pathogens. SHOULD THESE BE ADDED, CHANGED OR REMOVED?  

 

Finally, the timeline of bacterial cycling is discussed in regard to the establishment of a new iAVs. 

 

5.1 NITRIFYING BACTERIA AND THE BIOFILTER 

SHOULD THESE BE ADDED, CHANGED OR REMOVED? SHOULD A SECTION ABOUT SIOL BIOLOGY BE INCLUDED??? WHY IS AMMONIUM NOT MENTIONED?

Chapter 2 discussed the vital role of nitrifying bacteria in regard to the overall iAVs process. 

 

The nitrifying bacteria convert the fish waste, which enters the system mainly as ammonia, into nitrate, which is fertilizer for the plants (Figure 5.1). This is a twostep process, and two separate groups of nitrifying bacteria are involved. The first step is converting ammonia to nitrite, which is done by the ammonia-oxidizing bacteria (AOB). These bacteria are often referred to by the genus name of the most common group, the Nitrosomonas. 

 

The second step is converting nitrite to nitrate is done by the nitrite-oxidizing bacteria (NOB). These are commonly referred to by the genus name of the most common group, the Nitrobacter. There are many species within these groups, but for the purposes of this publication, the individual differences are not important, and it is more useful to consider the group as a whole. The nitrification process occurs as follows: 

 

1) AOB bacteria convert ammonia (NH₃) into nitrite (NO₂- ) 

2) NOB bacteria then convert nitrite (NO₂- ) into nitrate (NO₃- )

 

REPLACE PICTURE

 

A healthy bacterial colony is essential to a functioning iAVs. 

 

Nitrifying Soil bacteria are relatively slow to reproduce and establish colonies, requiring days and sometimes weeks, and therefore the patience of the farmer is one of the most important management parameters when establishing a new iAVs. 

 

Many aquariums and aquaculture systems have failed because too many fish were added before the colony of bacteria was fully developed. AND/OR OVERFED

 

There are several other key parameters to support nitrifying bacteria. Generally, bacteria require a large, dark location to colonize with good water quality, adequate food and oxygen. 

 

Often, nitrifying bacteria form a slimy, light brown or beige matrix on the biofilter, and have a distinctive odour that is difficult to describe, but does not smell particularly foul which could indicate other micro-organisms. REMOVE?

 

5.1.1 High surface area 

 

Sand has a high specific surface area (SSA) ADD WHAT THE AMOUNT IS which is optimal to develop extensive colonies of nitrifying bacteria. SSA is a ratio defining the surface area exposed from a given volume of media, and is expressed in square metres per cubic metres (m2 /m3 ). 

 

The greater the surface area available for bacteria to colonize, the more efficient the biofiltration becomes.  

 

Further characteristics and SSA of the sand used in iAVs is summarized in Table 4.1 and Appendix 4.CHECK AND ADD INFO NEEDED  An oversized biofilter cannot harm an iAVs, and although overly large biofilters would add unnecessary expense, excess biofiltration capacity has saved many systems from collapse. 

 

5.1.2 Water pH 

SECTION NEEDS TO BE REWRITTEN OR REMOVED Nitrifying bacteria function adequately through a pH range of 6–8.5. 

 

Generally, these bacteria work better at higher pH, with the Nitrosomonas group preferring a pH of 7.2–7.8, and the Nitrobacter group preferring a pH of 7.2–8.2. 

 

However, the target pH for iAVs is 6.4, which is a compromise between all the organisms within this ecosystem. Nitrifying bacteria function adequately within this range, and any decrease in bacterial activity can be offset with a larger biofilter. ADD INFO AS TO WHY THIS IS NOT AN ISSUE IN IAVS WITH EXCESS OXYGEN AND THE CHEMICAL REACTION REDUCING AMMONIA TO AMMONIUM ENABLING THE MICROBES TO FUNCTION BETTER

 

5.1.3 Water temperature 

 

The ideal temperature spectrum for the growth and activity of nitrifying bacteria lies between 17 and 34 degrees Celsius. 

 

A decrease in water temperature below this spectrum can lead to a reduction in bacterial productivity.

 

Specifically, the Nitrobacter group is less adaptable to colder temperatures compared to the Nitrosomonas group. Therefore, during colder times, it’s crucial to keep a closer eye on nitrite levels to prevent potentially harmful build-ups.

 

5.1.4 Dissolved oxygen 

 

Nitrifying bacteria need adequate levels of DO in the water at all times to grow healthily and maintain high levels of productivity. 

 

Nitrification is a reduction/oxidation (redox) reaction, where the bacteria derive the energy to live when oxygen is combined with the nitrogen. 

 

Optimum levels of DO are 4–8 mg/litre, which is also the level required for the fish and the plants. 

 

Nitrification does not occur if the DO concentration drops below 2 mg/litre. Ensure adequate biofiltration by dedicating aeration to the biofilter, either through flood-and-drain cycles in media beds, air stones in external biofilters, or cascading water return lines to the canals and sump tanks. MAYBE REWRITE THIS AND ADD MISSING INFO ABOUT ATMOSPHERIC OXYGEN AND FORCED CONTACT AND THAT PERHAPS (CHECK) MENTION THAT DO IS LESS IMPORTANT THAN IN OTHER SYSTEMS

 

5.1.5 UV light 

SKIPPED

 

5.1.6 Monitoring bacterial activity 

 

If all of these five parameters are respected, it is safe to assume that the bacteria are present and functioning properly. REMOVE OR CHANGE THIS? That said, bacteria are so important to iAVs that it is worth knowing the overall health of the bacteria at any given time. 

 

However, bacteria are microscopic organisms, and it is impossible to see them without a microscope. There is a simple method to monitor the bacterial function; testing for ammonia, nitrite and nitrate provides information on the health of the bacterial colony. 

 

Ammonia and nitrite should always be 0–1 mg/litre in a functioning and balanced iAVs. If either is detectable, it indicates a problem with the nitrifying bacteria. There are two possible, common reasons for this to occur. 

 

First, the biofilter is too small for the amount of fish and fish feed. Therefore, there is an imbalance and there are too many fish. To rectify, either increase the biofilter size or reduce the number of fish, or the fish feeding regime. 

 

Sometimes, this problem can occur when the system started out balanced when the fish were smaller, but gradually became unbalanced as the fish grew and were fed more with the same size biofilter. THIS IS WHY WE START HARVESTING AT 250GRAMS – ADD LINK TO SECTION ON FISH

 

Second, if the system is balanced in size, then the bacteria themselves may not be functioning properly. This could indicate a problem with the water quality, and each parameter listed above should be checked. Often, this can occur during winter seasons as the water temperature begins to fall and bacterial activity slows. 

 

5.2 HETEROTROPHIC BACTERIA AND MINERALIZATION

IS THIS GOING TO OPEN A CAN OF WORMS – REMOVE IT OR REWRITE IT ALL?? THIS S DISCUSSED ALSO IN THE BIOFILTER SECTION SO THIS NEEDS TO MOVE THERE OR VICE VERSA! 

 

There is another important bacteria group, as well as other microorganisms, involved in iAVs. This bacteria group is generally called the heterotrophic group. These bacteria utilize organic carbon as its food source, and are mainly involved in the decomposition of solid fish and plant waste. 

 

Most fish only retain 30–40 percent of the food they eat, meaning that 60–70 percent of what they eat is released as waste. 

 

Of this waste, 50–70  percent is dissolved waste released as ammonia. However, the remaining waste is an organic mix containing proteins, carbohydrates, fats, vitamins and minerals. The heterotrophic bacteria metabolize these solid wastes in a process called mineralization, which makes essential micronutrients available for plants in iAVs CONFIRM THIS (Figure 5.2). 

 

These heterotrophic bacteria, as well as some naturally occurring fungi, help decompose the solid portion of the fish waste. In doing so, they release the nutrients locked in the solid waste into the water

 

This mineralization process is essential because plants cannot take up nutrients in solid form. The wastes must be broken into simple molecules in order to be absorbed by plants’ roots. 

 

Heterotrophic bacteria feed on any form of organic material, such as solid fish waste and even dead bacteria. There are many sources of food available for these bacteria in an iAVs. 

 

Heterotrophic bacteria require similar growing conditions to the nitrifying bacteria, especially in high levels of DO AND/OR AN ABUNDANCE OF OXYGEN. The heterotrophic bacteria colonize all components of the biofilter, but are especially concentrated in the furrows where the solid waste accumulates. 

 

Heterotrophic bacteria grow much faster than the nitrifying bacteria, reproducing in hours rather than days. In the biofilter, the wastes collect in the furrows, and many heterotrophic bacteria are found here.

 

Mineralization is important because it releases several micronutrients that are necessary to plant growth. Without mineralization, some plants may experience nutrient deficiencies and would need supplemental fertilizer. 

 

Heterotrophic bacteria are aided in the decomposition of solid waste by a community of other organisms. Often, earthworms, isopods, amphipods, larvae and other small animals can be found in an iAVs biofilter. CHANGE THIS SO IT DESCRIBES A SOIL ECOSYSTEM AND NOT AN AQUACULTURE SYSTEM These organisms work together with the bacteria to decompose the solid waste, and having this community can prevent accumulation of solids.

 

5.3 UNWANTED BACTERIA 

 

5.3.1 Sulphate reducing bacteria 

SHOULD THIS BE REMOVED SINCE ANAEROBIC ZONES ARE NOT AN ISSUE? Nitrifying and mineralizing bacteria are useful to an iAVs, but some other types of bacteria are harmful. One of these harmful groups of bacteria is the sulphate reducing group. These bacteria are found in anaerobic conditions (no oxygen), where they obtain energy through a redox reaction using sulphur. The problem is that this process produces hydrogen sulphide (H2S), which is extremely toxic to fish. These bacteria are common, found in lakes, saltmarshes and estuaries around the world, and are part of the natural sulphur cycle. These bacteria are responsible for the odour of rotten eggs, and also the grey-black colour of sediments. The problem in aquaponics is when solid wastes accumulate at a faster pace than the heterotrophic bacteria and associated community can effectively process and mineralize them, which can in turn lead to anoxic festering conditions that support these sulphate-reducing bacteria. In high fish density systems, the fish produce so much solid waste that the mechanical filters cannot be cleaned fast enough, which encourages these bacteria to multiply and produce their noxious metabolites. Large aquaponic systems often contain a degassing tank where the hydrogen sulphide can be released safely back to the atmosphere. Degassing is unnecessary in small-scale systems. However, even in small-scale systems, if a foul odor is detected, reminiscent of rotten eggs or raw sewage, it is necessary to take appropriate management action. These bacteria only grow in anoxic conditions, so to prevent them, be sure to supply adequate aeration and increase mechanical filtration to prevent sludge accumulation. 

 

5.3.2 Denitrifying bacteria

SKIPPED AS NO ANAEROBIC ZONES

 

5.3.3 Pathogenic bacteria 

 

A final group of unwanted bacteria are those that cause diseases in plants, fish and humans. These diseases are treated separately in other parts of this publication, with Chapters 6 and 7 discussing plant and fish disease, respectively, and Section 8.6 discussing human safety. 

 

Overall, it is important that there are good agricultural practices (GAPs) that mitigate and minimize the risk of bacterial diseases within an iAVs. Prevent pathogens from entering the system by: ensuring good worker hygiene; preventing rodents from defecating in the system; keeping wild mammals (and dogs and cats) away; avoiding using water that is contaminated; and being aware that any live feed can be a vector for introducing alien micro-organisms into the system. It is especially important not to use rainwater collection from roofs with bird faeces unless the water is treated first. 

 

The major risk from warm-blooded animals is the introduction of Escherichia coli, and birds often carry Salmonella spp.; dangerous bacteria can enter the system with animal faeces. 

 

Second, after prevention, never let the water come into contact with the leaves of the plants. This can be accomplished by sizing the ridges appropriately to suit the size of the plants being grown AND ALSO TRIMMING THE BOTTOM SECTIONS OF THE PLANTS. This prevents many plant diseases as well as potential contamination of fish water to human produce, especially if the produce is to be eaten raw. 

 

Always wash vegetables before consumption, iAVs or otherwise. Generally, common sense and cleanliness are the best guards against diseases. Additional sources for food safety are provided throughout this publication and in the section on Further Reading.

 

5.4 SYSTEM CYCLING AND STARTING A BIOFILTER COLONY

System cycling is a term that describes the initial process of building a bacterial colony when first starting any RAS, including an iAVs. Under normal circumstances, this takes 3–5  weeks; cycling is a slow process that requires patience. 

 

SHOULD THIS BE LISTED AS OPTIONAL – OR CHANGED TO JUST USE INOCULANT OR COMPOST INSTEAD OF AMMONIA?

 

Overall, the process involves constantly introducing an ammonia source into the iAVs feeding the new bacterial colony. The progress is measured by monitoring the nitrogen levels. 

 

Generally, cycling takes place once a system is built, but it is possible to give the biofilter a head start when creating a new system. It is important to understand that during the cycling process there will be high levels of ammonia and nitrite, which could be harmful to fish. Also, make sure the biofilter and fish tank, are protected from direct sunlight before starting the process. 

 

Once introduced into the unit, the ammonia becomes an initial food source for the AOB, a few of which are naturally occurring and recruit to the system on their own. They can be found on land, in water and in the air. Within 5–7 days after the first addition of ammonia, the AOB start forming a colony and begin to oxidize the ammonia into nitrite. Ammonia should be continuously, but cautiously, added to ensure adequate food for the developing colony without becoming toxic. 

 

After another 5–7 days the nitrite levels in the water will have started to rise, which in turn attracts the NOB. As the NOB populations increase, the nitrite levels in the water will start to decline as nitrite is oxidized into nitrate. The full process is illustrated in Figure 5.3, which shows the trends of ammonia, nitrite and nitrate in the water over the first 20–25 days of cycling. 

 

 

The end of the cycling process is defined as when the nitrate level is steadily increasing, the nitrite level is 0  mg/litre and the ammonia level is less than 1 mg/litre. In good conditions, this takes about 25–40  days, but if the water temperature is cool, complete cycling may take up to two months to finish. 

 

At this point, a sufficient bacterial colony has formed and is actively converting the ammonia to nitrate. The reason this process is long is that nitrifying bacteria grow relatively slowly, requiring 10–15 hours to double in population. 

 

However, some heterotrophic bacteria can double in as little as 20 minutes. Aquarium or aquaculture retailers sell various products containing living nitrifying bacteria (in a bottle). Once added to the unit, they immediately colonize a system thus avoiding the cycling process explained above. 

 

However, these products may be expensive or unavailable and ultimately unnecessary, as the cycling process can be achieved using organic means. Alternatively, if another aquatic system is available, it is extremely helpful to share part of the biofilter as a seed of bacteria for the new system. This greatly decreases the time necessary for cycling the system. 

 

It can also be useful to separately start a biofilter medium by continuously trickling a solution containing 2–3  mg/litre of ammonia for a few weeks in advance.

 

Many people use fish as the original source of ammonia in a new tank. However, these fish suffer the effects of high ammonia and high nitrite throughout the cycling process. Many new aquarists do not have the patience to allow a tank to fully cycle and the result is that the new fish die, commonly referred to as “new tank syndrome”. 

 

If using fish, it is recommended to use a very low stocking density (≤ 1 kg/m3 ). Instead of using fish, there are other sources of this initial ammonia to start feeding the biofilter colony. Some possible sources include fish feed, sterilized animal waste, ammonium nitrate fertilizer and pure ammonia. 

 

Each of these sources has positives and negatives, and some sources are far better and safer to use than others. The best ammonia source is finely ground fish food because it is a biologically safe product, and it is relatively easy to control the amount of ammonia being added (Figure  5.4). 

 

Be sure to use fresh, unspoiled and disease-free fish feed only. Chicken waste, despite being an excellent ammonia source, can be very risky and can introduce dangerous bacteria into the iAVs. Escherichia coli and Salmonella spp. are commonly found in chicken and other animal manure and, therefore, any manure must be sterilized before use. 

 

Household ammonia products can be used, but be sure that the product is 100 percent ammonia and does not include other ingredients such as detergents, colourants or heavy metals that could ruin the entire system. 

 

Once the ammonia source has been selected, it is important to add the ammonia slowly and consistently, and to monitor the nitrogen levels every 2–3  days (Figure  5.6). 

 

It is useful to record levels on a graph to track the process of the cycling. It is important not to add too much ammonia, and it is better to have a little bit too little than too much. The target level is 1–2  mg/litre. If ammonia levels ever exceed 3 mg/litre, it is necessary to do a water exchange to dilute the ammonia in order to prevent it from inhibiting the bacteria. 

5.4.1 Adding fish and plants during the cycling process 

 

Plants and fish should be added only after the cycle is complete. CONFIRM  Plants can be added a little bit earlier, but expect nutrient deficiencies in these early plants during this period because other nutrients take time to reach optimal concentrations.

 

Only once the ammonia and nitrite levels are below 1 mg/litre it is safe to start stocking the fish. Always start stocking the fish slowly. 

 

Once fish have been stocked, it is not uncommon to see a secondary and smaller ammonia and nitrite spike. This happens if the ammonia created from the newly stocked fish is much greater than the daily ammonia amounts added during the cycling process. 

 

NOT SURE IF ANY OF THIS IS A PROBLEM (OR NEEDED) IN IAVS?

 

Continue to monitor the levels of all three types of nitrogen, and be prepared to do water exchanges if ammonia or nitrite levels rise above 1 mg/litre while the system continues to cycle.

 

THE SECTION BELOW MAY NEED TO REPLACE OR BE INCORPORATED WITH THE SECTION ABOVE

 

Inoculating an Integrated AquaVegeculture System

To set up an iAVs, follow these steps:

1. Introducing Fingerlings and Plants
  • Add the first batch of young fingerlings, weighing between 5 to 10 grams, to the two culture tanks.
  • Introduce a small batch of plants to the respective two modules of sand beds, divided into six modules in total.
2. Feeding and Monitoring
  • Feed the fish at a reduced rate, gradually increasing it in direct proportion to plant growth and water quality factors.
  • As the system normalizes, incrementally increase the plant population based on the feed input.
3. Inoculating the System
  • To ‘jump-start’ the system, inoculate it with a suspension of Nitrosomonas and Nitrobacter bacteria, which can reduce the initial cycling time to a few days.
  • One such product is Fritz-Zyme #7, REMOVE MENTION OF PRODUCT NAME? which can be used at approximately half the recommended concentration for near-immediate results.
  • The fish added in step 1 ensure a source of ammonia is available for the bacteria to survive and multiply.
4. Alternative Inoculation Methods
  • If you have access to well-developed organic compost, sprinkle a small handful into the furrows nearest the water inlet end to inoculate the media with indigenous strains of amoeba, mycorrhiza, nematodes, protozoa, etc., and accelerate the development of soil microflora.
  • Another possible inoculant source is a small amount of very humus-rich soil, using only a couple of tablespoons per furrow to initiate the process.

 

5.5 CHAPTER SUMMARY

 

  • The most important factors for good nitrification are: high surface area media for bacteria to grow and colonize; pH (6.4); and water temperature (17–34 °C).
  • System cycling is the initial process of building a nitrifying bacteria colony in a new iAVs. This 3–5 week process involves adding an ammonia source into the system (fish feed, ammonia-based fertilizer, up to a concentration in water of 1-2 mg/litre) in order to stimulate nitrifying bacteria growth. This should be done slowly and consistently. Ammonia, nitrite, and nitrate are monitored to determine the status of the biofilter: the peak and subsequent drop of ammonia is followed by a similar pattern of nitrite before nitrate starts to accumulate. Fish and plants are only added when ammonia and nitrite levels are low and the nitrate level begins to rise. IS THE LAST LINE ACCURATE OR NEEDED?
  • Ammonia and nitrite tests are used to monitor the function of the nitrifying bacteria and the performance of the biofilter. In a functioning system, ammonia and nitrite should be close to 0 mg/litre. High levels of either ammonia or nitrite require a water change and management action. Usually, poor nitrification is due to a change in water temperature, DO or pH levels.
  • Ammonia and nitrite tests are used to monitor the function of the nitrifying bacteria and the performance of the biofilter. In a functioning system, ammonia and nitrite should be close to 0 mg/litre. High levels of either ammonia or nitrite require a water change and management action. Usually, poor nitrification is due to a change in water temperature, DO or pH levels.

 

6. Plants

 

This chapter discusses the theory and practice needed for successful plant production in iAVs.

 

First, there is a discussion on some essential plant biology and plant nutrition concepts, focusing on the most important aspects for iAVs. After, there is a brief section on recommendations for selecting vegetables to grow.

 

 The final two sections cover plant health, methods to maintain plant health, and some advice on how to make the most of the plant growing space. 

 

In many commercial ventures, the vegetable production is more profitable than the fish. However, there are exceptions, and some farmers earn more from particularly valuable fish.

 

Estimates from commercial aquaponic units predominantly in the West suggest that up to 90 percent of the financial gains can come from plant production. One reason is the fast turnover rate of vegetables compared with the fish. 

 

Further information on plant production is covered in Chapter 8 and in the appendixes.  Appendix 1 is a technical description of 12 popular vegetables to grow; Appendix 2 contains descriptions and tables detailing several organic treatments of pests and diseases.

 

6.1 MAJOR DIFFERENCES BETWEEN SOIL AND SOIL-LESS CROP PRODUCTION 

REMOVE OR REWRITE THIS SECTION

 

There are many similarities between in-ground soil-based agriculture and soilless production, while the basic plant biology is always the same (Figures  6.1). 

 

However it is worth investigating major differences between soil and soil-less production (Table  6.1) in order to bridge the gap between traditional in-ground practices and newer soil-less techniques. Generally, the differences are between the use of fertilizer and consumption of water, the ability to use non-arable land, and overall productivity. In addition, soil-less agriculture is typically less labour-intensive. Finally, soil-less techniques support monocultures better than does in-ground agriculture.

 

6.1.1 Fertilizer 

 

Soil chemistry, especially relating to the availability of nutrients and the dynamics of fertilizers, is a full discipline and fairly complex. Fertilizer addition is required for intensive in-ground cultivation. However, farmers cannot fully control the delivery of these nutrients to plants because of the complex processes occurring in the soil, including biotic and abiotic interactions. The sum of these interactions determines the availability of the nutrients to the plant roots. 

 

6.1.2 Water use 

 

Water use in iAVs is much lower than in soil production. 

 

Water is lost from in-ground agriculture through evaporation from the surface, transpiration through the leaves, percolation into the subsoil, runoff and weed growth. 

 

However, in iAVs, the only water use is through crop growth and transpiration through the leaves. The water used is the absolute minimum needed to grow the plants, and only a negligible amount of water is lost for evaporation.

 

Overall, iAVs uses only about 10 percent CHECK THE AMOUNT AS IT’S PROBABLY HIGHER of the water needed to grow the same plant in soil. 

 

Thus, iAVs has great potential to allow production where water is scarce or expensive.

 

6.1.3 Utilization of non-arable land 

 

iAVs can be used in areas with non-arable land. 

 

One common place for iAVs is in urban and peri-urban areas that cannot support traditional soil agriculture. iAVs can be used on the ground floor, in basements (using grow lights) or on rooftops. 

 

Urban-based agriculture can also reduce the production footprint because transport needs are greatly reduced; urban agriculture is local agriculture and contributes to the local economy and local food security. 

 

Another important application for iAVs is in other areas where traditional agriculture cannot be employed, such as in areas that are extremely dry (e.g. deserts and other arid climates), where the soil has high salinity (e.g. costal and estuarine areas or coral sand islands), where the soil quality has been degraded through over-use of fertilizers or lost because of erosion or mining, or in general where arable land is unavailable owing to tenure, purchase costs and land rights. 

 

Globally, the arable land suitable for farming is decreasing, and iAVs is one method that allows people to intensively grow food where in-ground agriculture is difficult or impossible. 

 

6.1.4 Productivity and yield 

 

The most intensive hydroponic culture can achieve 20–25 percent higher yields than the most intensive soil-based culture, although rounded down data by hydroponic experts claim productivity 2–5  times higher. This is when hydroponic culture uses exhaustive greenhouse management, including expensive inputs to sterilize and fertilize the plants. Even without the expensive inputs, the aquaponic techniques described in this publication can equal hydroponic yields and be more productive than soil. The main reason is the fact that soil-less culture allows the farmer to monitor, maintain and adjust the growing conditions for the plants, ensuring optimal real-time nutrient balances, water delivery, pH and temperature. In addition, in soil-less culture, there is no competition with weeds and plant benefit from higher control of pests and diseases.

 

6.1.5 Reduced workload 

 

Soil-less culture does not require ploughing, tilling, mulching or weeding. On large farms, this equates to lower reliance on agriculture machinery and fossil fuel usage. In small-scale agriculture, this equates to an easier, less labour-intensive exercise for the farmer, especially because most aquaponic units are raised off the ground, which avoids stooping. Harvesting is also a simple procedure compared with soil-based agriculture, and products do not need extensive cleaning to remove soil contamination. Aquaponics is suitable for any gender and many age classes and ability levels of people. 

 

6.1.6 Sustainable monoculture 

 

With soil-less culture, it is entirely possible to grow the same crops in monoculture, year after year. In-ground monocultures are more challenging because the soil becomes “tired”, loses fertility, and pests and diseases increase. In soil-less culture, there is simply no soil to lose fertility or show tiredness, and all the biotic and abiotic factors that prevent monoculture are controlled. However, all monocultures require a higher degree of attention to control epidemics compared with polyculture.

 

6.1.7 Increased complication and high initial investment 

 

The labour required for the initial set-up and installation, as well as the cost, can discourage farmers from iAVs. Aquaponics is a fairly complex system and requires daily management of three groups of organisms. If any one part of the system fails, the entire system can collapse. In addition, aquaponics requires reliable electricity. Overall, aquaponics is far more complicated than soil-based gardening. Once people are familiar with the process, aquaponics becomes very simple and the daily management becomes easier. There is a learning curve, as with many new technologies, and any new aquaponic farmer needs to be dedicated to learn. Aquaponics is not appropriate for every situation, and the benefits should be weighed against the costs before embarking on any new venture

 

6.2 BASIC PLANT BIOLOGY 

 

This section comments briefly on the major parts of the plant and then discusses plant nutrition (Figure 6.3). 

 

Further discussion is outside the scope of this publication, but more information can be found in the section on Further Reading.

 

6.2.1 Basic plant anatomy and function 

 

Roots 

 

Roots absorb water and minerals from the soil. Tiny root hairs stick out of the root, helping the absorption process. Roots help to anchor the plant in the soil, preventing it from falling over. Roots also store extra food for future use. 

 

Roots in soil-less culture show interesting differences from standard in-ground plants. In soil-less culture, water and nutrients are constantly supplied to the plants, which are facilitated in their nutrient search and can grow faster. Root growth in hydroponics can be significant for the intense uptake and the optimal delivery of phosphorus that stimulates their growth. 

 

It is worth noting that roots retain almost 90 percent of the metals absorbed by the plants, which include iron, zinc and other useful micronutrients.

 

Stems 

 

Stems are the main support structure of the plant.

 

They also act as the plant’s plumbing system, conducting water and nutrients from the roots to other parts of the plant, while also transporting food from the leaves to other areas. Stems can be herbaceous, like the bendable stem of a daisy, or woody, like the trunk of an oak tree. 

 

Leaves 

 

Most of the food in a plant is produced in the leaves. Leaves are designed to capture sunlight, which the plant then uses to make food through a process called photosynthesis. Leaves are also important for the transpiration of water. 

 

Flowers 

 

Flowers are the reproductive part of most plants. Flowers contain pollen and tiny eggs called ovules. After pollination of the flower and fertilization of the ovule, the ovule develops into a fruit. 

Fruit/seeds 

 

Fruits are developed parts of flower ovaries that contain seeds. 

 

Fruits include apples, lemons, and pomegranates, but also include tomatoes, eggplants, corn kernels and cucumbers. The latter are considered fruits in a botanical sense because they contain seeds, though in a culinary definition they are often referred to as vegetables.

 

Seeds are the reproductive structures of plants, and fruits serve to help disseminate these seeds. Fruiting plants have different nutrient requirements than leafy green vegetables, especially requiring more potassium and phosphorous. 

 

6.2.2 Photosynthesis 

 

All green plants are designed to generate their own food using the process of photosynthesis (Figure 6.4). 

 

Photosynthesis requires oxygen, carbon dioxide, water and light. 

 

Within the plant are small organelles called chloroplasts that contain chlorophyll, an enzyme that uses the energy from sunlight to break apart atmospheric carbon dioxide (CO2) and create high-energy sugar molecules such as glucose. 

 

Essential to this process is water (H2O). This process releases oxygen (O2), and is historically responsible for all the oxygen in the atmosphere. 

 

Once created, the sugar molecules are transported throughout the plant and used later for all of the physiological processes such as growth, reproduction and metabolism. 

 

At night, plants use these same sugars, as well as oxygen, to generate the energy needed for growth. This process is called respiration. 

 

Respiration occurs when glucose (sugar produced during photosynthesis) combines with oxygen to produce usable cellular energy. This energy is used to fuel growth and all of the normal cellular functions. 

 

Respiration occurs in all living cells, including leaves and roots, and does not require light energy, so it can be conducted at night or during the day.

 

It is vital to locate an iAVs in a place where each plant will have access to sunlight. This ensures adequate energy for photosynthesis. Water should always be available to the roots through the system. 

 

Carbon dioxide is freely available from the atmosphere, although in very intensive indoor culture it is possible that plants use all the carbon dioxide in the enclosed area and require ventilation.

 

6.2.3 Nutrient requirements 

 

In addition to these basic requirements for photosynthesis, plants need a number of nutrients, also referred to as inorganic salts. These nutrients are required for the enzymes that facilitate photosynthesis, for growth and reproduction. These nutrients can be sourced from the soil. 

 

In iAVs, all of these essential nutrients come from the fish waste. There are two major categories of nutrients: macronutrients and micronutrients. Both types of nutrient are essential for plants, but in differing amounts. Much larger quantities of the six macronutrients are needed compared with the micronutrients, which are only needed in trace amounts. 

 

Although all of these nutrients exist in solid fish waste, some nutrients may be limited in quantity in aquaponics and result in deficiencies, e.g. potassium, calcium and iron. MENTION HOW THE FISH FOODS CAN BE CHANGED TO FIX THIS AND ALSO MENTION WHAT HAPPENED IN THE IAVS RESEARCH

 

A basic understanding of the function of each nutrient is important to appreciate how they affect plant growth. If nutrient deficiencies occur, it is important to identify which element is absent or lacking in the system and adjust the system accordingly by adjusting the type of fish feed used or increase the feed amount.

 

Macronutrients 

 

There are six nutrients that plants need in relatively large amounts. These nutrients are nitrogen, phosphorous, potassium, calcium, magnesium and sulphur.

 

The following discussion outlines the function of these macronutrients within the plant. Symptoms of deficiencies are also listed in order to help identify problems.

 

Nitrogen 

 

NEED TO ADD MENTION OF AMMONIUM   (N) is the basis of all proteins. It is essential for building structures, photosynthesis, cell growth, metabolic processes and the production of chlorophyll. 

 

As such, nitrogen is the most common element in a plant after carbon and oxygen, both of which are obtained from the air. 

 

Nitrogen is therefore the key element in the aquaponic nutrient solution and serves as an easy-to-measure proxy indicator for other nutrients. 

 

Usually, dissolved nitrogen is in the form of nitrate, but plants can utilize moderate quantities of ammonia and even free amino acids to enable their growth. 

 

Nitrogen deficiencies are obvious, and include yellowing of older leaves, thin stems, and poor vigour (Figure 6.5a). 

 

Nitrogen can be reallocated within plant tissues and therefore is mobilized from older leaves and delivered to new growth, which is why deficiencies are seen in older growth. 

 

An overabundance of nitrogen can cause excess vegetative growth, resulting in lush, soft plants susceptible to disease and insect damage, as well as causing difficulties in flower and fruit set.

 

Phosphorus 

 

(P) is used by plants as the backbone of DNA (deoxyribonucleic acid), as a structural component of phospholipid membranes, and as adenosine triphosphate (the component to store energy in the cells). 

 

It is essential for photosynthesis, as well as the formation of oils and sugars. It encourages germination and root development in seedlings. 

 

Phosphorous deficiencies commonly cause poor root development because energy cannot be properly transported through the plant; older leaves appear dull green or even purplish brown, and leaf tips appear burnt. 

 

Potassium 

 

(K) is used for cell signalling via controlled ion flow through membranes. 

 

Potassium also controls stomatic opening, and is involved in flower and fruit set. It is involved in the production and transportation of sugars, water uptake, disease resistance and the ripening of fruits. Potassium deficiency manifests as burned spots on older leaves and poor plant vigour and turgor (Figure 6.5b). 

 

Without potassium, flowers and fruits will not develop correctly. Interveinal chlorosis, or yellowing between the veins of the leaves, may be seen on the margins. 

 

Calcium 

 

(Ca) is used as a structural component of both cell walls and cell membranes.

 

It is involved in strengthening stems, and contributes to root development. Tip burn of lettuces and blossom-end rot of tomatoes and zucchinis are examples of deficiency. 

 

Often, new leaves are distorted with hooked tips and irregular shapes. 

 

Calcium can only be transported through active xylem transpiration, so when conditions are too humid, calcium can be available but locked-out because the plants are not transpiring. Increasing air flow with vents or fans can prevent this problem. 

Magnesium 

 

(Mg) is the centre electron acceptor in chlorophyll molecules and is a key element in photosynthesis. 

 

Deficiencies can be seen as yellowing of leaves between the veins especially in older parts of the plant. 

 

Sulphur 

 

(S) is essential to the production of some proteins, including chlorophyll and other photosynthetic enzymes. 

The amino acids methionine and cysteine both contain sulphur, which contributes to some proteins’ tertiary structure. 

 

Deficiencies are rare, but include general yellowing of the entire foliage in new growth (Figure 6.5c). Leaves may become yellow, stiff and brittle, and fall off. 

 

Micronutrients 

 

Below is a list of nutrients that are only needed in trace amounts. 

 

Most micronutrient deficiencies involve yellowing of the leaves (such as iron, manganese, molybdenum and zinc). 

 

However, copper deficiencies cause leaves to darken their green colour. 

Iron 

 

(Fe) is used in chloroplasts and the electron transport chain, and is critical for proper photosynthesis. 

 

Deficiencies are seen as intervenous yellowing, followed by the entire foliage turning pale yellow (chlorotic) and eventually white with necrotic patches and distorted leaf margins. 

 

As iron is a non-movable element, iron deficiencies (Figure 6.5d) are easily identified if new leaves appear chlorotic. 

 

Iron has to be added as chelated iron, otherwise known as sequestered iron or Fe*EDTA, because iron is apt to precipitate at pH greater than 7. The suggested addition is 5 millilitres per 1 m2 of grow bed whenever deficiencies are suspected; a larger quantity does not harm the system, but can cause discolouration of tanks and pipes. It has been suggested that submerged magnetic-drive pumps can sequester iron and is the subject of current research.

Manganese 

 

(Mg) is used to catalyse the splitting of water during photosynthesis, and as such, manganese is important to the entire photosynthesis system. 

 

Deficiencies manifest as reduced growth rates, a dull grey appearance and intervenous yellowing between veins that remain green, followed by necrosis. 

 

Symptoms are similar to iron deficiencies and include chlorosis. 

 

Manganese uptake is very poor at pH greater than 8. 

Boron  

 

(B) is used as a sort of molecular catalyst, especially involved in structural polysaccharides and glycoproteins, carbohydrate transport, and regulation of some metabolic pathways in plants. 

 

It is also involved in reproduction and water uptake by cells. 

 

Deficiencies may be seen as incomplete bud development and flower set, growth interruption and tip necrosis, and stem and root necrosis. 

 

Zinc  

 

(Zn) is used by enzymes and also in chlorophyll, affecting overall plant size, growth and maturation. 

 

Deficiencies may be noticed as poor vigour, stunted growth with reduced inter-nodal length and leaf size, and intravenous chlorosis that may be confused with other deficiencies. 

 

Copper  

 

(Cu) is used by some enzymes, especially in reproduction. It also helps strengthen stems. 

 

Deficiencies may include chlorosis and brown or orange leaf tips, reduced growth of fruits, and necrosis. 

 

Sometimes, copper deficiency shows as abnormally dark green growth. 

 

Molybdenum

 

 (Mo) is used by plants to catalyse redox reactions with different forms of nitrogen. 

 

Without sufficient molybdenum, plants can show symptoms of nitrogen deficiency although nitrogen is present. 

 

Molybdenum is biologically unavailable at pH less than 5.

 

The availability of many of these nutrients depends on the pH (see Section  6.4 for pH-dependent availability), and although the nutrients may be present they may be unusable because of the water quality. 

 

For further details on nutrient deficiencies outside the scope of this publication, please refer to the section on Further Reading for illustrated identification guides. 

 

6.2.4 Sources of nutrients 

 

Nitrogen is supplied to plants mainly in the form of nitrate and ammonium. 

 

Some of the other nutrients are dissolved in the water from the fish waste, but most remain in a solid state that is unavailable to plants.

 

The solid fish waste is broken down by heterotrophic bacteria. The best way to ensure that plants do not suffer from deficiencies is to maintain the optimum water pH (6.4) and feed the fish a balanced and complete diet, and use the feed rate ratio to balance the amount of fish feed to plants. 

 

However, over time, even a perfectly balanced may become deficient in certain nutrients, most often iron potassium or calcium. Deficiencies in these nutrients are a result of the composition of the fish feed.

 

 Fish feed pellets (discussed in Chapter 7) are a complete food for the fish, meaning they provide everything that a fish needs to grow, but not necessarily everything needed for plant growth. 

 

Chapter 9 discusses how to produce simple organic fertilizers from compost to use as supplements to the fish waste, ensuring that the plants are always receiving the right amount of nutrients.

 

6.3 WATER QUALITY FOR PLANTS 

 

Section 3.3 discussed water quality parameters for the iAVs as a whole. 

 

Here, specific considerations for plants are considered and further expanded.

 

6.3.1 pH 

 

The pH is the most important parameter for plants in an iAVs because it influences a plant’s access to nutrients. 

 

In general, the tolerance range for most plants is 5.5–7.5. The lower range is below the tolerance for fish and bacteria, and most plants prefer mildly acidic conditions. 

 

If the pH goes outside this range, plants experience nutrient lockout, which means that although the nutrients are present in the water the plants are unable to use them. This is especially true for iron, calcium and magnesium. 

 

Sometimes, apparent nutrient deficiencies in plants actually indicate that the pH of the system is outside the optimal range. Figure  6.6 describes the relationship between pH level and the ability for plants to take-up certain nutrients. 

 

iAVs is an entire ecosystem. As such, there are biological interactions occurring between the plant roots, bacteria and fungi that may allow nutrient uptake even at higher pH levels than those shown in Figure 6.6. However, the best course of action is to attempt to maintain pH slightly acidic 6.4 (+/- 0.4 )

6.3.2 Dissolved oxygen 

 

Most plants need high levels of DO (> 3 mg/litre) within the water. 

 

Plants use their stems and leaves to absorb oxygen during respiration, but the roots also need to have oxygen. 

 

Without oxygen, the plants can experience root-rot, a situation where the roots die and fungus grows. Some water plants, such as water chestnut, lotus or taro, do not need high levels of DO and can withstand low-oxygen waters such as those in stagnant ponds. SHOULD THIS SECTION BE REMOVED?

 

6.3.3 Temperature and season 

 

The suitable temperature range for most vegetables is 18–30  °C. However, some vegetables are far more suited to growing in particular conditions. 

 

For the purposes of this publication, winter vegetables require temperatures of 8–20  °C, and summer vegetables require temperatures of 17–30 °C. For example, many leafy green vegetables grow best in cooler conditions (14–20 °C), especially at night. In higher temperatures of 26 °C and above, leafy greens bolt and begin to flower and seed, which makes them bitter and unmarketable. 

 

Generally, it is the water temperature that has the greatest effect on the plants rather than the air temperature. Nevertheless, care should be taken in the correct choice of plants and fish to meet their optimal water temperature ranges. 

 

Another aspect of seasonal planting is that some plants require a certain amount of daylight to produce flowers and fruit, which is called photoperiodism. 

 

Some, referred to as short-day plants, require a certain amount of darkness before flowering. This signal to the plant indicates that winter is approaching, and the plant puts its energy into reproduction instead of growth. 

 

Some commonly grown, short-day plants include varieties of peppers and certain medicinal flowers. 

 

On the other hand, longday plants require a certain day length before producing flowers, although this is rarely a consideration in vegetables but may be so for some ornamentals. As such, it is important to follow the local seasonal planting practices for each vegetable grown or to choose varieties that are neutral to photoperiodism. 

 

Appendix 1 contains further details on individual vegetables.

 

6.3.4 Ammonia, nitrite and nitrate 

 

WHY IS AMMONIUM NOT ADDED HERE? As explained in Chapter 2, plants are able to take up all three FOUR forms of nitrogen, but nitrate is the most accessible. Ammonia and nitrite are very toxic to fish and should always be maintained below 1 mg/litre. IS THIS REFERRING TO AMMONIA ITSELF OR THE TAN? In a functioning iAVs, ammonia and nitrite are always 0–1 mg/litre and should not be a problem for the plants. 

 

6.4 PLANT SELECTION 

 

To date, more than 150 different vegetables, herbs, flowers and small trees have been grown successfully in iAVs, including research, domestic and commercial units. Appendix 1 provides a technical summary of, and detailed growing instructions for, the 12  most popular herbs and vegetables. 

 

In general, leafy green plants do extremely well in iAVs along with some of the most popular fruiting vegetables, including tomatoes, cucumbers and peppers. 

 

Vegetables vary regarding their overall nutrient demand. There are two general categories of plants based on this demand. Low-nutrient-demand plants include the leafy greens and herbs, such as lettuce, chard, salad rocket, basil, mint, parsley, coriander, chives, pak choi and watercress. Many of the legumes such as peas and beans also have low-nutrient demands. 

 

At the other end of the spectrum are plants with high-nutrient demand, sometimes referred to as nutrient hungry. These include the botanical fruits, such as tomatoes, eggplants, cucumbers, zucchini, strawberries and peppers. Other plants with medium nutrient demands are: cabbages, such as kale, cauliflower, broccoli and kohlrab. 

 

Bulbing plants such as beets, taro, onions and carrots have medium to high requierements, while radish requires less nutrients. 

 

Provided the biofilter is  the right depth (at least 30  cm), it is possible to grow all the vegetables mentioned in the categories above. Polyculture on small surfaces can also take advantage of companion planting (see Appendix 2) and better space management, because shade-tolerant species can grow underneath taller plants. 

 

Fruiting plants need to be positioned over a larger distance than leafy vegetables. This is because fruiting plants grow larger and need more light to ripen their fruits. 

 

It is important to consider the effect of harvesting the plants on the entire ecosystem. If all the plants were to be harvested at once, the result would be an unbalanced system without enough plants to clean the water, resulting in nutrient spikes. 

 

Some farmers use this technique, but it must correspond with a large fish harvest or a reduction of the feed ration. However, the recommendation here is to use a staggered harvesting and replanting cycle. The presence of too many plants growing synchronously would result in the systems being deficient in some nutrients towards the harvest period, when the uptake is at a maximum. 

 

By having plants at different life stages, i.e. some seedlings and some mature, the overall nutrient demand is always the same. This ensures more stable water chemistry, and also provides a more regular production both for the home table and the market. Staggered planting schemes are discussed in more detail in Chapter 8

 

6.5 PLANT HEALTH, PEST AND DISEASE CONTROL 

 

Plant health has a broad meaning that goes far beyond just the absence of illnesses; it is the overall status of well-being that allows a plant to achieve its full productive potential. 

 

Plant health, including disease prevention and pest deterrence and removal, is an extremely important aspect of iAVs food production (Figure 6.8). 

 

Although the most important advances in plant health have been achieved through the management of pathogens and pests, optimal nutrition, intelligent planting techniques and proper environmental management are also fundamental to secure healthy plants.

 

In addition, knowledge on the specific plants grown is fundamental to addressing various production issues. 

 

Although some basic concepts on plant nutrition have already been described, this section aims to provide a far greater understanding on how to minimize the risks and to address plant diseases and pests in small-scale systems. For more information on beneficial insects, including insect characteristics and climatic needs, along with general information on pest identification, as well as integrated pest and disease management (including different products available for treatment), see Appendix 2 and the resources listed in the section on Further Reading.

 

6.5.1 Plant pests, integrated production and pest management 

 

Insect pests are problematic for plant production because they carry diseases that plants can contract. 

 

Pests also extract liquids as they bore into plant tissues, leading to stunted growth. Controlled environments, such as greenhouses, can be particularly problematic for pests because the enclosed space provides favourable conditions for insects without rain or wind. 

 

Pest management for outdoor conditions also differs from that in protected cultivation (net houses, greenhouses), due to the physical separation of the plants from the surrounding area, which allows the use of beneficial insects indoor to kill/control the insect pests. Insect pest prevalence is also highly dependent on climate and environment. Pest management in temperate or arid zones is easier than in tropical regions, where higher incidence and competition among insects make pest control a far more difficult task. 

 

An iAVs is an independent ecosystem, and so it is normal for a host of micro-organisms and small insects and spiders to exist within the biofilter. 

 

However, other harmful insect pests, such as whiteflies, thrips, aphids, leaf miners, cabbage moths and spider mites feed upon and damage the plants. 

 

A common practice for dealing with problematic insect pests in land-based vegetable production is to use chemical pesticides or insecticides, but this is impossible in iAVs. Any strong chemical pesticide could be fatal for fish as well as the beneficial bacteria living in system. Therefore, commercial chemical pesticides must never be used. However, there are other effective physical, environmental and cultural controls to reduce the threat of pests. 

 

Insecticides and deterrents should be considered a last resort. Nevertheless, successful management integrates crop and environmental management with the use of organic and biological pest deterrents. 

 

Integrated production and pest management (IPPM) is an ecosystem approach to soil-based plant production and protection that combines different management strategies and practices to grow healthy plants and minimize pesticide use. It is a combination of mechanical, physical, chemical, biological and microbial controls along with host-plant resistance and cultural practices. 

 

Not all of these controls are applicable for iAVs as some may be fatal for fish and bacteria (i.e. chemical and some organic pesticides) while others may not be economically justified for a small scale iAVs (i.e. microbial control agents). 

 

Thus, this section concentrates on the most applicable strategies, including mechanical and physical control, host plant resistance and cultural techniques to prevent the threat of pests and diseases. 

 

Some brief comments are given on some iAVs-safe biological controls (i.e. beneficial insects and microorganisms), and more details are included in Appendix  2. For further information on these methods, see the section on Further Reading. 

 

Physical, mechanical and cultural controls 

 

For pest management in iAVs, prevention is fundamental. 

 

Regular and thorough monitoring for pests is vital, and, ideally, minor infestations can be identified and managed before the insects damage the entire crop. 

 

Below is a list of simple inexpensive controls used in organic/conventional agriculture, which are also suitable for a small scale iAVs, to avoid pest infestations. 

 

Physical exclusion refers to keeping the pests away. 

 

Mechanical removal is when the farmer actively takes the pests away from the plants. 

 

Cultural controls are the choices and management activities that the farmer can undertake to prevent pests. 

 

These controls should be used as a first line of defence against insect pests before other methods are considered.

 

Netting/screens 

 

This method is common to prevent pest damage in tropical regions or wherever organic horticulture is practised or pesticides are not effective. Netting mesh size varies depending on the pest targeted; use nets with a mesh size of 0.15 mm to exclude thrips, 0.35 mm to exclude whitefly and aphids, and 0.8 mm to keep out leaf miners. 

 

Netting is particularly effective while the seedlings are very young and tender. Screens do not suppress or eradicate pests, they only exclude most of them; therefore, they must be installed prior to pest appearance and care should be taken not to let pests enter into the protected environment. 

 

Physical barriers 

 

Given the limited distances that insects can cover, it is possible to reduce pest prevalence by adding physical barriers between the vegetables and the surrounding vegetation such as paved surfaces or building stories. 

 

Rooftop iAVs production benefits from the natural ventilation, given the higher altitude, and the large physical barrier (distance from the ground) creating ideal conditions for outdoor production relatively free from pests and diseases. 

 

Greenhouses often have a strong fan blowing out through the entrance way that can help to prevent insects from entering with the farmer. Another useful technique, for raised biofilters, is to create a barrier. 

 

A ring of copper flashing can prevent snails and slugs from climbing up, and a coating of petroleum jelly can prevent ants. 

 

Hand inspection and removal 

 

The removal, either by hand or using a high-pressured stream of water, of heavily infested leaves or plants helps to avoid and/or to delay the spread of insects to surrounding plants (Figure 6.10). 

 

Larger pests and larvae may also be used as supplementary food for the fish. 

 

Water sprayed from a hose directed at the underside of the leaves is an extremely effective management technique on many types of sucking insects. The stream can actually kill some insects, and the others are washed away. This is effective on sucking insects such as aphids and whiteflies. This is one of the most effective methods on small-scale systems, but it can be just a temporary remedy as the displaced pests can return to the plants. It can use significant volumes of water and become too labour-intensive with larger systems.

 

Trapping 

 

Sticky traps positioned slightly above the canopy of plants are effective in protected environments (e.g. net houses, greenhouses). Blue sticky cards trap adult stages of thrips while yellow sticky cards trap whiteflies and microlepidoptera (Figure  6.11). 

 

Sticky traps are less effective in outdoor conditions as new insects can easily come from the surrounding areas. The continuous monitoring of insects being captured by the traps can help a farmer to adopt specific measures to reduce the occurrence of certain pests. 

 

Another effective way of dealing with pests is to use pheromone-baited traps. These attract males of specific pests, thereby reducing the mating population in the area.

 

Environmental management 

 

Maintain optimal light, temperature and humidity conditions, which can be easily changed in protected cultivation, to favour healthier plant growth and to build unfavourable conditions for pests. 

 

For example, spider mites do not tolerate wet and humid conditions, so timed misters directed on the plant leaves can deter infestations.

 

Plant choice 

 

Some pests are more attracted to specific plant species than others. 

 

Similarly, different plant varieties from the same species have different resistance/tolerance to pests. This is one reason that polyculture can often prevent large infestations because some plants remain unaffected. 

 

Moreover, some plants attract and retain more beneficial insects to help manage pest populations (discussed in more detail below). Choose resistant varieties from local suppliers and agriculture extension agents to help reduce diseases and infestations.

Indicator plants and sacrificial/catch/trap crops 

 

Some plants, such as cucumber and legumes, are more prone to aphids or red mite infestations and thus can be used to detect pest prevalence early. 

 

Often, indicator plants are planted along the exterior edge of larger gardens. Another strategy that can be adopted in iAVs is the use of biological insecticides on sacrificial or “catch plants” planted near to, but not within, the iAVs. 

 

Catch plants (i.e. fava beans) attract pests. These plants can be grown in pots beside the iAVs, attracting the pests away from the unit, which are then treated with insecticides (see below). This strategy would not affect the iAVs ecosystem or beneficial insects present around the unit. 

 

Although not purely organic, catch plants can even be treated with commercial synthetic insecticides if large infestations are present. Fava beans and petunias (flowers) can be used to catch thrips, aphids and mites. Cucumbers are also used to catch aphids and hoppers while succulent lettuce seedlings are used to capture other leaf-eating insects.

Companion planting 

 

Companion planting is the constructive use of plant relationships by growers. 

 

For example, all plants produce natural chemicals that they release from their leaves, flowers and roots. These chemicals may attract or repel certain insects and can enhance or limit the growth rate and yield of neighbouring plants. 

 

It is therefore important to be aware of which plants benefit from each other when planted together, and which plant combinations are best avoided. 

 

Appendix 2 provides a companion planting table to use when choosing crops. When using the companion table, concentrate on avoiding the bad companions rather than planning for good ones. 

 

Some plants release chemicals from their roots or leaves that either suppress or repel pests, which can serve to protect other neighbouring plants.

 

Fertilization 

 

As mentioned above, excessive nitrogen makes plants more prone to pest attack because they have more succulent tissues. 

 

A correct balance of nutrients using the feed rate ratio (see Chapters 2 and 8) helps plants to grow stronger in order to withstand pest attacks. 

Spacing 

 

High planting density and/or inadequate pruning increases competition for light, encouraging insect pests. This competition eventually makes plant tissue more succulent for pests to bore through or for pathogens to penetrate, and the cramped conditions offer shelter to the pests. 

 

Be sure that there is adequate ventilation and sunlight penetration through the canopy. As previously discussed, many plants have special needs for sunlight or a lack of it. By combining full-sun with shade-tolerant plants, it is possible to intensify the production without the risk of raising competition and weakening the plants. In this case shade-tolerant plants can grow under the canopy of sun-loving ones. In this way, the plants are healthier and more resistant to pests and disease.

 

Crop rotation 

 

Growing the same species continuously over multiple seasons can have a selective effect on the surrounding pests. Thus, a change in crop, even for a short period, may cause a drastic reduction of pests specifically targeting the monoculture crop. 

Sanitation 

The removal of all plant debris, including all roots, at the end of each harvest helps to reduce the incidence of pests and diseases. Dead leaves and diseased branches should be removed consistently. In outdoor conditions without nets, it is advisable to reduce the surrounding vegetation to a minimum in order to prevent pests spreading to the iAVs. 

Diseased plants and compost piles should be kept far from the system to prevent contamination.

Chemical controls 

If pests remain a problem after using the above physical, mechanical and cultural controls, it may be necessary to use chemical control. 

Synthetic pesticides and insecticides must never be used in iAVs because they will kill the fish. Many biological controls are also deadly to fish. All chemicals controls are to be considered a last resort in iAVs and only used sparingly. 

Appendix 2 contains a list of common insecticides and repellents, their indications and their relative toxicity to fish.

Biological controls 

As for botanical pesticides, some extracts obtained from micro-organisms are safe for aquatic animals because they act specifically on insect structures and do not harm mammals or fish. 

Two organisms widely used in organic agriculture are Bacillus thuringiensis and Beauveria bassiana. The former is a toxin extract from a bacterium that damages the insect’s digestive tract and kills it. It can be sprayed on leaves and specifically targets caterpillars, leaf rollers, moth or butterfly larvae without damaging other beneficial insects. B. bassiana is a fungus that germinates and penetrates the insect’s skin (chitin), killing the pest through dehydration. 

The efficacy of the fungus depends on the number of spores sprayed and on the optimal humidity and temperature conditions, ideally a good agent for humid tropics.

Beneficial insects – pest predators 

Finally, beneficial insects are another effective method to control pests, particularly in controlled environments such as greenhouses or nethouses. Beneficial or predator insects such as lacewings are introduced into the plant growing space in order to control any further infestation. 

Some of the advantages of using beneficial insects include: the absence of pesticide residue or pesticide-induced resistance in pests, economically feasible (in the long run for large-scale operations only), and ecologically sound. 

However, successful pest control using this method depends on detailed knowledge of each beneficial insect along with the constant monitoring of pests to time correctly the introduction of beneficial insects. 

Moreover, beneficial insects can be attracted naturally to outdoor systems. Many of these beneficial insects feed on nectar in their adult stages, so a selection of flowers near the iAVs can maintain a population that can keep pests in balance. It is important to underline that this method of control never fully eradicates the pests. Instead, pests are suppressed under a tight prey-predator relationship.

 The choice of beneficial insects to use (see Appendix  2) should take into account the environmental conditions where they are going to operate. 

6.5.2 Plant diseases and integrated disease management 

iAVs takes advantage of a complex microscopic ecosystem that includes bacteria, fungi and other micro-organisms. 

The presence of these well adapted micro-organisms makes each system more resilient in the event of attack by pests or diseases. Nevertheless, successful plant production is the result of management strategies to avoid disease outbreaks that mainly focus on the environmental conditions, pest deterrence (pests such as whitefly may carry lethal viruses) on plant management as well as the use of organic remedies that help to prevent or to cure the plants. 

Similar to IPPM, integrated disease management relies on prevention, plant choice, and monitoring as a first line of defence against disease, and uses targeted treatment only when necessary.

Environmental controls 

Temperature and humidity play an important role in the health management of plants. 

Each plant pathogen (i.e. bacteria, fungi or parasites; Figure 6.8) has optimal growth temperatures that can be different to those of plants. Thus, diseases occur in certain areas and periods during the year when conditions are more favourable to the pathogen than to its host. 

Moreover, moisture plays a key role for the germination of fungal spores, which require a thin film of water covering the plant tissues. Similarly, the activation of some bacterial and fungal diseases is strictly correlated with the presence of surface water. Therefore, the control of relative humidity and moisture are essential in order to reduce the risks of disease outbreaks. 

Appendix 2 contains detailed environmental conditions that encourage several common fungal diseases. 

Control of relative humidity, especially in a greenhouse, is particularly important. This can be achieved through dynamic or forced ventilation by means of windows and fans creating horizontal airflow helping to minimize temperature differentials and cold spots where condensation occurs. Moving air is continually mixed, which prevents the temperature dropping below the dew point; therefore, water does not condense on the vegetables. 

Evaporation from fish tanks should also be avoided by physically covering the water surfaces, as evaporated water can dramatically increase the indoor humidity. 

Systems built on rooftops have the advantage of a drier microclimate and good ventilation compared with ground level, which facilitates environmental management of plants. Control of water temperature plays a key role in avoiding fungal outbreaks.

Root rot, caused by Pythium spp., is a soil-borne pathogen that does not cause damage below certain temperatures because of the competitive presence of other micro-organisms. 

The maintenance of temperatures below 28–30 °C is thus essential in order to avoid the exponential germination of spores that would eventually cause an outbreak. Attention should also be given to planting densities. Very high densities reduce the internal ventilation and increase the humidity among the plants. 

The risk of diseases for densely planted crops is also enhanced as, under intense light competition, plants grow without consolidating their cells, leading to softer and more succulent tissues walls. Tender tissues are more prone to disease because of their limited resistance to pest and/or pathogen penetration.

Plant choice 

Plant varieties have different levels of resistances to pathogens. In some cases, using known resistant cultivars is the most successful method of avoiding disease. 

Thus, it is vital to select plant varieties that are more adapted to grow in certain environments or have a higher degree of resistance against a particular pathogen. Moreover, many seed compani

es offer a wide selection of plants that have different responses against pathogens. The use of local varieties that are naturally selected for a specific environment can ensure healthy plant growth. 

If it is not possible to control certain diseases with resistant varieties, it is wise to shift to other crops during the critical season. 

In the case of Pythium  spp. if resistant varieties of lettuce and beneficial micro-organisms are not able to control the infestation, it is opportune to shift to other species, such as basil, that are more tolerant to the pathogen and to high water temperatures. 

Seeds and/or seedlings must be bought from a reputable nursery that employs effective disease prevention strategies and can secure disease-free products. Moreover, avoid injury to plants, as broken branches, cracks, cuts and pest damage often lead to diseases breaking out in the same area.

Plant nutrition 

Nutrition greatly affects a plant’s susceptibility to disease. It also affects a plant’s ability to respond against disease using different mechanisms, including antixenosis (processes to deter colonization by herbivores) or antibiosis (processes to kill or reduce herbivores after landing or during eating). 

A correct balance of nutrients not only provides optimal growth but also makes plants less susceptible to diseases. 

Although the description of nutritional disorders has been discussed above, Table  6.2 outlines how some nutrients can play a major role in disease occurrence.

Monitoring – inspection and exclusion 

Early detection and intervention is the foundation of disease and pest management. Thus, plants should be inspected regularly for early signs of infection or pest presence that may result in infection. 

Whenever plants show signs of damage or initial stages of disease (wilt, blight or root rot), it is vital to remove the infected branches, leaves or the whole plant to avoid the disease spreading throughout the entire crop. 

Moreover, regarding exclusion, it is important to enforce the control of potential vectors (sources) of viruses, such as whiteflies, by growing plants in insect-proof structures (see Section  6.5.1). In addition, the avoidance of soil contamination as well as the use of disinfected tools (e.g. shears used for pruning/harvesting) would help to avoid the transmission of potential pathogens into the system. 

Finally, it is good practice to monitor and record all symptoms and the progression of each disease in order to determine the best prevention and treatment methods in the future. 

Treatment – inorganic or chemical 

As mentioned above, iAVs is a complex ecosystem that is very resilient. 

However, some disease outbreaks may still occur in the case of unfavourable environmental conditions, such as higher relative humidity in greenhouses or in tropical climates, and need to be controlled. 

As iAVs is an integrated system containing fish, plants and beneficial micro-organisms, it is not possible to use the standard disease treatments of conventional agriculture (i.e. chemical fungicides) as they are toxic to fish. 

However, common practices used for organic agriculture are possible, provided that they do not harm fish and/or the bacteria or do not accumulate in the system leading to higher than accepted thresholds. 

Appendix 2 indicates elements and methods of application used in organic agriculture that can also be used for iAVs to fight and stave off different diseases. In general, successful treatment using the methods relies on the combination of a few strategies that can have synergic effect against specific pathogens.

Treatment – biological 

Some biological control agents can be used for iAVs such as Thricoderma spp., Ampelomices spp. and Bacillus subtilis, which are cultured micro-organisms used to fight against specific diseases. 

These biological agents can be applied either on leaves or at the root zone. They provide protection against the most common soil-borne diseases including downy mildew, powdery mildew and some bacteria. In particular, Thricoderma spp. have proved effective in controlling Pythium spp. and most of the soil-borne pathogens, while Ampelomices spp. could offset any need for inorganic or chemical treatments against powdery mildew. In the case of Thricoderma spp., the spores can be distributed on substrate when seeding, to let the beneficial fungus protect plants starting at their seedling stage. 

Product information, producers and distributors should be consulted before use in order to identify the best treatment methods for specific diseases. For more detailed information on specific vegetable diseases including identification, susceptibility and prevalence, see recommended texts in the section on Further Reading.

6.6 PLANTING DESIGN 

The layout of the grow beds helps to maximize plant production in the available space. 

Before planting, choose wisely which plants will be grown, bearing in mind the space needed for each plant and what the appropriate growing season is. 

A good practice for all garden design is to plan the layout of the grow beds on paper in order to have a better understanding of how everything will look. Important considerations are: plant diversity, companion plants and physical compatibility, nutrient demands, market demands, and ease of access. 

For example, taller crops (i.e. tomatoes) should be placed in the most accessible place within the media bed to make harvesting easier.

Encouraging plant diversity 

In general, planting various crops and varieties provides a degree of security to the grower. All plants are susceptible to some kinds of disease or parasites. If only one crop is grown, the chance for a serious infestation or epidemic is higher. This can unbalance the system as a whole. As such, growers are encouraged to plant a diverse range of vegetables in small-scale units.

Staggered planting 

As mentioned previously, it is important to stagger planting. In this way, there can be constant harvest and replanting, which helps to maintain a balanced level of nutrients in the unit. 

At the same time, it provides a steady supply of plants to the table or market. Keep in mind that some plants produce fruit or leaves that can be harvested continually throughout a season, such as salad leaf varieties, basil, coriander and tomatoes, whereas some other crops are harvested whole, such as kohlrabi, lettuce, carrots. 

To achieve staggered planting there should always be a ready supply of seedlings (the development of a plant nursery is discussed in Chapter 8).

Maximizing space in media beds 

Not only should the surface area be planned out to maximize space, but also the vertical space and time should be considered. 

For example, in regard to time, plant vegetables with short grow-out periods (salad greens) between plants with longer-term crops (eggplant). The benefit of this practice is that the salad greens can be harvested first and provide more room as the eggplants mature. 

Continued replanting of tender vegetables such as lettuce in between large fruiting plants provides naturally shaded conditions. 

Make sure that the shaded crops are not completely dominated as the large crops mature. Vegetables such as cucumbers are natural climbers that can be trained to grow up or down and away from the beds. 

Use wooden stakes and/or string to help support the climbing vegetables. This creates more space in the biofilter. 

One of the benefits of iAVs is that plants can be easily moved by gently freeing the roots and placing the plant in a different spot. 

6.7 CHAPTER SUMMARY

  • The major advantages of iAVs (Integrated AquaVegeculture System) over traditional soil agriculture are:

 

  1. No wasted fertilizer: iAVs recirculates water and nutrients, reducing the need for additional fertilizers and minimizing nutrient pollution from agricultural runoff.
  2. Lower water use: iAVs uses less water compared to traditional irrigation methods, as water is recirculated within the system, reducing the overall water consumption.
  3. Higher productivity/quality: iAVs can result in higher crop yields and better quality produce due to the controlled environment and efficient nutrient delivery.
  4. Ability to utilize non-arable land: iAVs can be set up on land that is not suitable for traditional agriculture, expanding the potential for food production in areas with poor soil quality or limited water resources.
  5. Offset of tillage, weeding, and other traditional agricultural tasks: iAVs reduces the need for labor-intensive tasks such as tillage and weeding, as the system is soil-based and plants are grown in a controlled environment.
  • Plants require sunlight, air, water, and nutrients to grow. Essential macronutrients include nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur. Micronutrients include iron, zinc, boron, copper, manganese, and molybdenum. Deficiencies can be prevented by ensuring a properly balanced fish food is used.
  • The most important water quality parameter for plants is pH because it affects the availability of essential nutrients. 
  • The suitable temperature range for most vegetables is 18-27°C, although many vegetables are seasonal. The optimal temperature for vegetable storage depends on whether they are cool-season or warm-season crops. 
  • All types of plants can grow well in iAVs, including root crops and tubers, although they are less commonly grown. 
  • Integrated production and pest/disease management uses a combination of methods to minimize pests and pathogens while ensuring the safety of fish and other organisms in the system. 
  • Intelligent planting design can maximize space, encourage beneficial insects, and improve production in a garden. 
  • Staggered planting provides continual harvest as well as a constant nutrient uptake and more consistent water quality. 

7. Fish in aquaponics

The first section in this chapter includes select information on fish anatomy and physiology, including how they breathe, digest food and excrete wastes.

 

The feed conversion ratio (FCR) is introduced, important for all aquaculture, which refers to how efficiently the fish convert feed into body mass. 

 

Special attention is then devoted to the fish life cycle and reproduction as it relates to breeding and maintaining stocks. The care and health of fish in iAVs are then discussed, covering water quality, oxygen, temperature, light and nutrition. 

 

The third section identifies a number of suitable commercial aquatic species for iAVs, focusing on tilapia, carp, catfish, trout, bass and prawns (Figure 7.1). 

 

The chapter closes with a final section on individual fish heath, diseases and disease prevention methods.

 

7.1 FISH ANATOMY, PHYSIOLOGY AND REPRODUCTION 

 

7.1.1 Fish anatomy

 

Fish are a diverse group of vertebrate animals that have gills and live in water. A typical fish uses gills to obtain oxygen from the water, while at the same time releasing carbon dioxide and metabolic wastes (Figure 7.2). 

 

The typical fish is ectothermic, or cold-blooded, meaning that its body temperature fluctuates according to the water temperature. 

 

Fish have almost the same organs as terrestrial animals; however, they also possess a swim bladder. Positioned in the abdomen, this is a vesicle containing air that keeps the animal neutrally buoyant in the water. 

 

Most fish use fins for movement and have a streamlined body for navigating through water. Often, their skin is covered with protective scales. Most fish lay eggs.

 

Fish have well-developed sensory organs allowing them to see, taste, hear, smell and touch. In addition, most fish have lateral lines, which sense pressure differences in the water.

 

Some groups can even detect electrical fields, such as those created by heartbeats of prey species. However, their central nervous system is not as well developed as in birds or mammals.

 

Main external anatomical features 

 

Eyes

 

Fish eyes are very similar to those of terrestrial animals, such as birds and mammals, except their lenses are more spherical. Some fish, such as trout and tilapia, rely on sight to find prey while other species use mainly their sense of smell.

 

Scales

Scales provide protection for the fish by acting as a shield against predators, parasites, diseases and physical abrasion.

Mouth and jaws

 

Fish ingest food through the mouth and break it down in the gullet. Often, the mouth is relatively large, allowing the ingestion of substantial prey. Some fish have teeth, including sometimes on the tongue. Fish breathe by bringing water in through the mouth and expelling it through the operculum.

 

Gill cover/operculum

 

This is the external covering of the gills, which offers protection to these delicate organs. It is often a bony plate and can be seen opening and closing while the fish is breathing.

 

Vent

 

This is the external opening on the bottom of the body near the tail. Solid wastes and urine pass through the digestive track, through the anus, and are expelled through the vent. 

 

In addition, the vent is where reproductive gametes (sperm and eggs) are released. The vent has a similar function to a cloaca. 

 

Fins

 

Paired fins, both the pectoral fins and pelvic fins, are located on the bottom of the fish body. They provide manoeuvrability and steering control. 

 

Odd fins, the dorsal fins and anal fins can be found on the top and bottom of the body and provide balance and stability as well as steering control. 

 

The tail fin is at the opposite end from the head and provides the main propulsion and movement for the fish. Fins often have sharp spines, sometimes with attached poison sacs, that are used for defence.

 

Respiration

 

Fish breathe oxygen using their gills, which are located in each side of the head area. 

 

Gills consist of structures called filaments. Each filament contains a blood vessel network that provides a large surface area for the exchange of oxygen and carbon dioxide. 

 

Fish exchange gases by pulling oxygen-rich water through their mouths and pumping it over their gills, releasing carbon dioxide at the same time. In their natural habitat, oxygen is supplied either by aquatic plants that produce oxygen through photosynthesis or from water movements such as waves and wind that dissolve atmospheric oxygen into the water. 

 

Without adequate DO, most fish suffocate and die. That is why adequate aeration is so crucial to successful aquaculture. 

 

However, some fish are equipped with an air breathing organ, similar to lungs, that allows them to breathe out of water. Clariidae catfish are one such group of fish that are important in aquaculture.

 

Excretion 

 

Nitrogen wastes are created as fish digest and metabolize their feed. 

 

These wastes come from the breaking down of proteins and the reuse of the resulting amino acids. These nitrogenous wastes are toxic to the body and need to be excreted. Fish release these wastes in three ways. 

 

First, ammonia diffuses into the water from the gills. If ammonia levels are high in the surrounding water, the ammonia does not diffuse as readily, which can lead to ammonia accumulation in the blood and damage to internal organs. 

 

Second, fish produce large quantities of very dilute urine that is expelled through their vents. Some nitrogen (proteins, amino acids, ammonia) is also present in the solid wastes that are expelled through the vent. 

 

Fish use kidneys to filter their blood and concentrate the waste for disposal. The excretion of urine is an osmotic regulation process, helping fish to maintain their salt content. 

 

Freshwater fish do not need to drink, and in fact need to actively expel water to maintain physiologic balance. 

 

7.1.2 Fish reproduction and life cycle 

 

Almost all fish lay eggs that develop outside of the mother’s body; indeed, 97 percent of all known fish are oviparous. 

 

Fertilization of the eggs by the sperm, known as milt in fish biology, also occurs externally in most cases. Male and female fish both release their sex cells into the water. 

 

Some species maintain nests and provide parental care and protection of the eggs, but most species do not attend the fertilized eggs which simply disperse into the water column. 

 

Tilapias are one example of fish that have extensive parental care, taking the time to maintain nests and actually brood the young fry in the mouth of the females. 

 

The reproductive organs of fish include testes, which make sperm, and ovaries, which make eggs. 

 

Some fish are hermaphrodites, having both testes and ovaries, either simultaneously, or at different phases in their life cycle. 

 

For the purposes of this publication, an average fish will pass through the life stages of egg, larvae, fry, fingerling, grow-out (adult fish) and sexual maturity (Figure 7.3).

 

 The duration of each of these stages is dependent on the species. 

 

The egg stage is often fairly brief and usually depends on water temperature. During this stage, the eggs are delicate and sensitive to physical damage. 

 

In culture conditions, the water needs to have adequate DO, but the aeration must be gentle. Sterile procedures and good hatchery practices prevent bacterial and fungal diseases of unhatched eggs. Once hatched, the young fish are called larvae. These small fish are usually poorly formed, carry a large yolk sac, and are often very different in appearance from juvenile and adult fish. The yolk sac is used for nourishment, and it is absorbed throughout the larval stage, which is also fairly short depending on temperature. 

 

At the end of the larval stage, when the yolk sac is absorbed and the young fish begin to swim more actively and move to the fry stage. 

 

At the fry and fingerling stage, fish begin to eat solid food. 

 

In the wild, this food is generally plankton found in the water column and algae from the substrate. During these stages, fish are voracious eaters, eating about 10  percent of their body weight per day. As the fish continue to grow, the percentage body weight of food per day decreases. The exact demarcations between fry, fingerlings and adult fish differ between species and between farmers. 

 

Generally, fry, fingerlings and juvenile fish need to be kept separate to prevent the larger fish from eating the smaller individuals. The grow-out stage is the stage that iAVs typically focuses on because this is when the fish are eating, growing and excreting wastes for the plants. Most fish are harvested during the grow-out stage. If fish are allowed to grow past this stage, they begin to reach sexual maturity, where their physical growth slows down as the fish devote more energy into the development of sex organs. 

 

Some mature fish need to be kept to complete the cycle during breeding operations, and these fish are often referred to as broodstock. 

 

Tilapias are exceptionally easy breeders, and can in fact breed too much for a small-scale system. 

 

Catfish, carp and trout require more careful management, and it may be better to source fish from a reputable supplier. It is outside the scope of this publication to detail aquaculture breeding techniques, but please refer to the section on Further Reading for helpful sources. 

 

7.2 FISH FEED AND NUTRITION 

7.2.1 Components and nutrition of fish feed

Fish require the correct balance of proteins, carbohydrates, fats, vitamins and minerals to grow and be healthy. This type of feed is considered a whole feed. 

 

Commercially available fish feed pellets are highly recommended for small-scale iAVs, especially at the beginning. It is possible to create fish feed in locations that have limited access to manufactured feeds. 

 

However, these home-made feeds need special attention because they are often not whole feeds and may lack in essential nutritional components. More on homemade feeds can be found in Section 9.11 and Appendix 5. 

 

Protein is the most important component for building fish mass. In their grow-out stage, omnivorous fish such as tilapia and common carp need 25–35 percent protein in their diet, while carnivorous fish need up to 45 percent protein in order to grow at optimal levels. In general, younger fish (fry and fingerlings) require a diet richer in protein than during the grow-out stage. 

 

Proteins are the basis of structure and enzymes in all living organisms. Proteins consist of amino acids, some of which are synthesized by the fishes’ bodies, but others which have to be obtained from the food. These are called essential amino acids. Of the ten essential amino acids, methionine and lysine are often limiting factors, and these need to be supplemented in some vegetable-based feeds. 

 

Lipids are fats, which are high-energy molecules necessary to a fish’s diet. Fish oil is a common component of fish feeds. Fish oil is high in two special types of fats, omega-3 and omega-6, that have health benefits for humans. The amount of these healthy lipids in farmed fish depends on the feed used. 

 

Carbohydrates consist of starches and sugars. This component of the feed is an inexpensive ingredient that increases the energy value of the feed. The starch and sugars also help to bind the feed together to make a pellet. However, fish do not digest and metabolize carbohydrates very well, and much of this energy can be lost. 

 

Vitamins and minerals are necessary for fish health and growth. Vitamins are organic molecules, synthesized by plants or through manufacturing, that are important for development and immune system function. 

 

Minerals are inorganic elements. These minerals are necessary for the fish to synthesis their own body components (bone), vitamins and cellular structures. Some minerals are also involved in osmotic regulation.

 

7.2.2 Pelletized fish feed 

 

There are a number of different sizes of fish feed pellets, ranging from 2  to 10  mm (Figure 7.4). 

 

The recommended size of these pellets depends on the size of the fish. Fry and fingerlings have small mouths and cannot ingest large pellets, while large fish waste energy if the pellets are too small. If possible, the feed should be purchased for each stage of the lifecycle of the fish. 

 

Alternatively, large pellets can be crushed with a mortar and pestle to create powder for fry and crumbles for fingerlings. Another method is to always use medium-sized pellets (2–4 mm). This way, fish are able to eat the same-sized pellet from the fingerling stage right up to maturity. 

 

Fish feed pellets are also designed to either float on the surface or sink to the bottom of the tank, depending on the feeding habits of the fish. It is important to know the eating behaviour of the specific fish and supply the correct type of pellet. 

 

Floating pellets are advantageous because it is easy to identify how much the fish are eating. It is often possible to train fish to feed according to the food pellets available; however, some fish will not change their feeding culture. 

 

Feed should be stored in dark, dry, cool and secure conditions. Warm wet fish feed can rot, being decomposed by bacteria and fungi. These micro-organisms can release toxins that are dangerous to fish; spoiled feed should never be fed to fish. Fish feed should not be stored for too long and should be purchased fresh and used immediately to conserve the nutritional qualities, wherever possible. 

 

Avoid overfeeding 

 

Uneaten food waste should never be left in the iAVs. Feed waste from overfeeding is consumed by heterotrophic bacteria, which consume substantial amounts of oxygen. In addition, decomposing food can increase the amount of ammonia and nitrite to toxic levels in a relatively short period.

 

In general, fish eat all they need to eat in a 30 minute period. After this length of time, remove any food. If uneaten food is found, lower the amount of feed given the next time. Further feeding strategies are discussed in Section 8.4.

 

7.2.3 Feed conversion ratio for fish and feeding rate 

 

The FCR describes how efficiently an animal turns its food into growth. It answers the question of how many units of feed are required to grow one unit of animal – FCRs exist for every animal and offer a convenient way to measure the efficiency and costs of raising that animal. Fish, in general, have one of the best FCRs of all livestock. In good conditions, tilapias have an FCR of 1.4–1.8, meaning that to grow a 1.0 kg tilapia, 1.4–1.8 kg of food is required. 

 

Tracking FCR is not essential in small-scale iAVs, but it can be useful to do in some circumstances. When changing feeds, it is worth considering how well the fish grow in regard to any cost differences between the feeds. 

 

Moreover, when considering starting a small commercial system, it is necessary to calculate the FCR as part of the business plan and/or financial analysis. Even if not concerned about the FCR, it is good practice to periodically weigh a sample of the fish to make sure they are growing well and to understand the balance of the system (Figure 7.5). 

 

7.2.4 Integrated AquaVegeculture System (iAVs): Feed and Ratio Guidelines

 

THIS WAS ADDED FROM IAVS AND NEEDS TO BE INCORPORATED OR REPLACE THE SECTION ABOVE  This section provides a comprehensive guide on the optimal feed rates, water-to-sand ratios, and fish densities for a successful iAVs setup.

Feed Rates

A long-term average feed rate of approximately 150 g/m3/day is considered viable, potentially more with continuous or vigorous plant production. During system start-up, with small fish and young plants, one can feed as much as the fish will eat twice a day. The feed input should increase as both the fish and plants grow. For instance, an initial feed rate during the first start-up could be 40 g/m3/day, increasing to 120 g/m3/day or more within a couple of weeks.

 

The amount of feed input determines the amount of fish ‘waste’ generated, which in turn dictates the appropriate filter volume. More feed results in more ‘waste’, requiring more filter surface and more soil biology to process.

Water-to-Sand Ratio

The optimal water-to-sand ratio depends on several factors, but a ratio of 1:2.4 or 1:1.5 is generally recommended. For first-time adopters, a volume-to-volume (v:v) ratio of 1:2 (or volume-to-area (v:a) ratio of 1:6) is suggested. This ratio is suitable for growing 80 to 100 tilapia per cubic meter from 15 g to 250+/- gram in 3 to 4 months, assuming they are fed a balanced ration twice a day.

Fish Density

In terms of fish density, a study found that 80 fish per cubic meter (at an initial weight of 15 g) performed well across all v:v ratios from 1:0.67 to 1:2.25. At a v:v ratio of 1:2, one should be able to do well at 100 fish per cubic meter, reducing the number when attaining an average size of 250 +/- 50 g.

Observations and Adjustments 

 

It’s important to note that there is no one-size-fits-all number for feeding rate. Variables such as feed composition, fish species, growth phases, sand and water qualities, and plant species and growth phases all play a role. Observing the fish’s feeding behavior and the plants’ growth rate and foliar symptoms can provide valuable insights into whether they are getting enough nutrients. As the system matures, the feed rate should be approximately balanced with the average plant nutrient uptake.

 

This also provides a more accurate growth rate expectation for harvest timing and production. As with all fish handling, weighing is easier in darkness to avoid stressing the fish. Box 3 lists simple steps for weighing fish. Weighing fish of the same age growing in the same tank is in general more preferable than heterogeneous cohorts of fish because the measurement should provide more reliable averages.  

 

Periodical weight measurements will give the average growth rate of the fish, which will be obtained by subtracting the average fish weight, calculated above, over two periods. The FCR is obtained by dividing the total feed consumed by the fish by the total growth during a given period, with both values expressed in the same weight unit (i.e. kilogram, gram).

 

Total feed / Total growth = FCR

 

The total feed can be obtained by summing all the recorded amount of feed consumed each day. The total growth can be calculated by simply multiplying the average growth rate by the number of the fish stocked in the tank. 

 

At the grow-out stage, the feeding rate for most cultured fish (as discussed in this publication) is 1–2 percent of their body weight per day. On average, a 100  gram fish eats 1–2 grams of pelletized fish feed per day. 

 

Monitor this feeding rate at the same time as the FCR to determine growth rates and fish appetite and to help maintain overall system balance.

 

7.2.5 iAVs Feeding and Pump Schedule

 

It is essential to maintain a proper feeding and pump schedule to ensure the health and growth of both fish and plants. The following schedule outlines the recommended timings for feeding fish and operating the pump cycles:

Feeding Times

  • 6:00 am (dawn or pre-dawn): Start the first pump cycle of the day.
  • 6:30 am: Drainage completed. Feed fish all they will eat in 15 minutes.
  • 1:45 pm: Feed fish all they will eat in 15 minutes.

Pump Cycles

  • 8:00 am: 2nd pump cycle (1/4 of tank volume, each).
  • 10:00 am: 3rd pump cycle.
  • 12:00 pm: 4th pump cycle.
  • 2:00 pm: 5th pump cycle.
  • 4:00 pm: 6th pump cycle.
  • 6:00 pm: 7th pump cycle.
  • 8:00 pm: 8th pump cycle (dusk or slightly after, depending on season and location).

By following this schedule, you can ensure that your iAVs system operates efficiently and provides the necessary nutrients for both fish and plants to thrive.

 

7.3 WATER QUALITY FOR FISH 

 

Chapter 2 discussed water quality. Here, the most important water quality parameters are listed again briefly and summarized in Table 7.1  WHY LIST THEM AGAIN??

 

7.3.1 Nitrogen 

 

WHY IS AMMONIUM NOT MENTIONED?  Ammonia and nitrite are extremely toxic to fish, and sometimes referred to as “invisible assassins”. 

 

Ammonia and nitrite are both considered toxic above levels of 1  mg/litre, although any level of these compounds contributes to fish stress and adverse health effects. There should be close to zero detectable levels of both of these in a seasoned iAVs. The biofilter is entirely responsible for transforming these toxic chemicals into a less toxic form

 

Any detectable levels indicate that the system is unbalanced with an undersized biofilter or that the biofilter is not functioning properly. Ammonia is more toxic in warm basic conditions; if the pH is high, any detectable amount of ammonia is especially dangerous. 

 

Water tests for ammonia are called total ammonia nitrogen (TAN), and test for both types of ammonia (ionized and un-ionized). Symptoms of ammonia and nitrite poisoning are often seen as red streaking on the fish body, gills and eyes, scraping on the sides of the tank, gasping at the surface for air, lethargy and death. 

 

Nitrate on the other hand is much less toxic to most fish. Most species are able to tolerate levels of more than 400 mg/litre.

 

7.3.2 pH 

 

Fish can tolerate a fairly wide range of pH, but do best at levels of 6.5–8.5. Substantial changes in pH in short periods (changes of 0.3 within a period of 12–24 hours) can be problematic or even lethal for fish. NEEDS CONFIRMATION 

 

Therefore, it is important to keep the pH as stable as possible. Buffering with carbonate is recommended to prevent large pH swings.

 

7.3.3 Dissolved oxygen 

 

Overall, as much DO as possible should be added to the iAVs. 

 

In practice, most fish require 4–5 mg/litre. Most domestic growers do not have the ability to check the oxygen level in their units because digital oxygen meters are expensive and cheaper aquarium test kits are not widely available. 

 

Even so, following these recommendations ensures adequate DO levels. Do not overstock the fish, and refrain from adding more than 20 kg of fish per 1 000 litres of total water. NEED TO CONFIRM 

 

Dynamic water flow, with cascading water falling back into the system, helps to aerate the water and add DO. Air pumps, if at all feasible, should be used. The suggested rate is 5–8 litres of air per minute for each cubic metre of water, coming from at least 2 air stones in different locations in the fish tank. 

 

Densely stocked units may require considerably more. Make sure that the water is not churned too vigorously or in a way that disrupts the fish swimming. A clear sign for lack of oxygen is when fish are gasping for air at the surface. This behaviour, called piping, is when fish swim close to the surface of the water and take air into their mouths. This is an emergency situation that needs immediate attention. 

 

Backup (redundant) aeration systems are a valuable asset to an iAVs and can be used during power outages and equipment failures; simple battery backups for air pumps have saved countless fish throughout the industry.

 

7.3.4 Temperature 

 

Fish are cold-blooded and, therefore, their ability to adjust to a large range of water temperatures is low. 

 

A steady temperature within their correct tolerance range keeps fish in their optimal conditions and aids fast growth and efficient FCR. In addition, optimal temperatures (and thus less stress) reduce the risk of diseases. 

 

Thermal isolation, water heaters and coolers help to achieve a steady temperature level, although these may be costly in areas where energy is expensive. It is often better to grow fish adapted to local environmental conditions. Each fish has an optimum temperature range that should be researched by the farmer. 

 

Generally, tropical fish thrive at 22–32 °C while cold-water fish prefer 10–18  °C. Meanwhile some temperate water fish have wide ranges, for example, common carp and largemouth bass can tolerate 5–30 °C.

 

7.3.5 Light and darkness 

 

The light level in the fish tank should be reduced to prevent algae growth. However, it should not be completely dark, as fish experience fear and stress when a completely dark tank is exposed to sudden light when uncovered. 

 

The ideal condition is with indirect natural light through shading, which would both prevent algal growth and avoid stress to fish. It is also recommended to handle, harvest or grade fish in darkness to reduce fish stress to a minimum.

 

7.4 FISH SELECTION 

 

Fish species suitable for iAVs include: tilapia, common carp, silver carp, grass carp, barramundi, jade perch, catfish, trout, salmon, Murray cod, and largemouth bass. Some of these species, which are available worldwide, grow particularly well in iAVs and are discussed in more detail in the following sections. 

 

In planning an iAVs, it is critical to appreciate the importance of the availability of healthy fish from reputable local suppliers. Some cultured fish have been introduced to areas outside their natural habitat, such as tilapia and a number of carp and catfish species. 

 

Many of these introductions have been through aquaculture. It is also important to be aware of local regulations governing the importation of any new species. Exotic (i.e. non-native) species should never be released into local bodies of water. Local extension agents should be contacted for more information regarding invasive species and native species suitable for farming.

 

7.4.1 Tilapia 

 

Main commercial types: 

 

Blue tilapia (Oreochromis aureus) Nile tilapia (Oreochromis niloticus) Mozambique tilapia (Oreochromis mossambicus) Various hybrids combining these three species.

 

Description 

 

Native to East Africa, tilapias are one of the most popular freshwater species to grow in aquaculture systems worldwide (Figure 7.6). They are resistant to many pathogens and parasites and handling stress. They can tolerate a wide range of water quality conditions and do best in warm temperatures. 

 

Although tilapias briefly tolerate water temperatures extremes of 14 and 36 °C, they do not feed or grow below 17 °C, and they die below 12 °C. The ideal range is 27–30 °C, which ensures good growth rates. Therefore, in temperate climates, tilapias may not be appropriate for winter seasons unless the water is heated. 

 

An alternate method for cool climates is to grow multiple species throughout the year, rearing tilapias during the warmest seasons and switching to carp or trout during the winter. In ideal conditions, tilapias can grow from fingerling size (50 g) to maturity (500 g) in about 6 months. 

 

Tilapias are omnivores, meaning they eat both plant- and animal-based feed. Tilapias are candidates for many alternative feeds, discussed in Section 9.1.2. Tilapias have been fed duckweed, Azolla spp., Moringa olifera and other high-protein plants, but care must be used to ensure a whole feed (i.e. nutritionally complete). 

 

Tilapias eat other fish, especially their own young; when breeding, the tilapia should be separated by size. Tilapias less than 15 cm eat smaller fish, though when larger than 15 cm they are generally too slow and cease to be a problem. 

 

Tilapias are easy to breed in a small-scale and medium-scale iAVs. More information is available in the section on Further Reading, but a brief discussion is outlined below. 

 

One method is to use a large iAVs for the grow-out stage. Two smaller separate fish tanks can then be used to house the broodstock and juveniles. 

 

A small separate iAVs can be used to manage the water quality in these two tanks, but may not be necessary with a low stocking density. Broodstock fish are hand-selected adults that are not harvested, and they are chosen as healthy specimens for breeding. 

 

Tilapias breed readily, especially where the water is warm, oxygenated, algae-filled and shaded, and in a calm and quiet environment. Rocky substrate on the bottom encourages nest building. The optimal ratio of males to females also encourages breeding; often, 2 males are paired with 6–10 females to initiate spawning. 

 

Tilapia eggs and fry are seen either in the mouths of the females or swimming on the surface. These fry can be transferred into juvenile rearing tanks, ensuring that no larger fingerlings are present that will eat them, and grown until they are large enough to enter the main culture tanks. 

 

Tilapias can be aggressive, especially in low densities, because males are territorial. Therefore, the fish should be kept at high densities in the grow-out tanks. Some farms only use male fish in the grow-out tanks; all male cultures of the same age grow larger and faster, because males do not divert energy in developing ovaries and do not stop feeding when spawning eggs as females do. 

 

Moreover, the growth rate in all-male tanks is not reduced by competition for food from fry and fingerlings, which are continuously produced if sexually mature males and females are left growing together. 

 

Monosex male tilapia can be obtained through hormone treatment or hand sexing of fingerlings. In the first case, fry are fed a testosterone-enriched feed during their first three weeks of life. High levels of the hormone in the blood cause a sex reversal in female fry. This technique, widely used in Asia and America but not in Europe (owing to different regulations), allows farmers to stock same-size male tilapia in ponds in order to avoid any problems of spawning and growth depression by feed competition from newer juveniles. 

 

Hand sexing simply consists of separating males from females by looking at their genital papilla when fish are about 40 g or larger. The process of identification is quite straightforward. In the vent region the males have only a single opening whereas females have two slits. 

 

The vent of the female is more “C” shaped, while in males the papilla is more triangular. As the fish grow larger, secondary characteristics can help identify males from females. Male fish have larger heads with a more pronounced forehead region, a humped back and more squared-off features. Females are sleeker and have smaller heads. Moreover, the fish’s behaviour can indicate the sex because males chase other males away and then court the females. 

Hand-sexing can be performed with small numbers of fish, as it does not take much time. However, this technique may not be practical in large-scale systems owing to the large numbers of fish being cultured. 

 

Nevertheless, mixed-sex tilapia can be reared in tanks until fish reach sexual maturity at the age of five months. Although females are relatively underperforming, they still do not cause problems with spawning and can be harvested at an earlier stage (200 g or more), leaving the males to grow further.

 

Nile Tilapia: A Resilient and Nutritious Choice for Integrated AquaVegeculture Systems

THIS ENTIRE SECTION BELOW THIS IS FROM IAVS A NEEDS TO BE COMBINED WITH THE SECTION ABOVE THIS

 

Resilience and Growth

Nile Tilapia, renowned for their robustness and adaptability, are often described as “almost bulletproof” due to their ability to thrive in diverse temperatures and conditions. Their resilience, coupled with their rapid growth, particularly in the case of all-male hybrid tilapia, makes them an ideal choice for Integrated AquaVegeculture Systems (iAVs), especially in regions where their cultivation is legally permitted1.

Nutritional Benefits

Consumption of Nile Tilapia offers a plethora of nutritional benefits. They are a rich source of protein, encompassing all nine essential amino acids required by the human body for growth and repair. Moreover, they are low in fat and calories, and provide vital vitamins such as B12 and niacin, along with selenium. The presence of omega-3 fatty acids in tilapia contributes to heart health.

Contribution to Plant Growth

Fish waste, a byproduct of iAVs, is rich in nutrients beneficial for plant growth. It contains essential macronutrients such as nitrogen, phosphorus, potassium, and calcium. Trace elements like iron, zinc, and manganese, present in fish waste, can also be advantageous in small quantities. The exact nutrient content per 100 grams varies with the type of fish, but generally, it is expected to contain around 0.5-1% nitrogen, 0.2-0.4% phosphorus, 1-3% potassium, and 2-6% calcium by weight.

The microflora in the fish’s digestive tract can contribute enzymes and hormones beneficial for plant growth. Enzymes like amylase, protease, and lipase aid in breaking down complex molecules into simpler forms that plants can more easily absorb. Hormones such as auxins and gibberellins play a crucial role in regulating plant growth processes like cell division and elongation.

Legal Considerations and Recommendations

In regions where tilapia cultivation is legal and the fish are readily available, they are highly recommended for iAVs. All-male hybrid tilapia, in particular, are preferred due to their rapid growth and larger size compared to females. Additionally, maintaining only male fish mitigates the risk of overpopulation resulting from reproduction.

 

7.4.2 Carp 

 

Main commercial types: 

 

Common carp (Cyprinus carpio) 

Silver carp (Hypophthalmichthys molitrix) 

Grass carp (Ctenopharyngodon idella)

 

Description 

 

Native to eastern Europe and Asia, carps are currently the most cultured fish species globally (Figure 7.7). 

 

Carp, like tilapia, are tolerant to relatively low DO levels and poor water quality, but they have a much larger tolerance range for water temperature. 

 

Carp can survive at temperatures as low as 4 °C and as high as 34 °C making them an ideal selection for iAVs in both temperate and tropical regions. Best growth rates are obtained when temperatures are between 25 °C and 30 °C. In these conditions, they can grow from fingerling to harvest size (500-600 g) in less than a year (10 months). 

 

Growth rates dramatically decrease with temperatures below 12  °C. Male carp are smaller than females, yet can still grow up to 40 kg and 1–1.2 m in length in the wild. 

 

In the wild, carps are bottom-feeding omnivores that eat a large range of foods. They have a preference for feeding on invertebrates such as water insects, insect larvae, worms, molluscs and zooplankton. Some herbivorous carp species also eat the stalks, leaves and seeds of aquatic and terrestrial plants, as well as decaying vegetation. 

 

Cultured carp can be easily trained to eat floating pellet feed. Carp fingerlings are best obtained from hatcheries and dedicated breeding facilities. The procedure to obtain juveniles is more complicated than tilapia because spawning in female carps is induced by hormone injection, a technique requiring additional knowledge of fish physiology and experience. 

 

Carps can easily be polycultured and this has been done for centuries. It mainly consists in culturing herbivorous fish (grass carp), planktivorous fish (silver carp) and omnivorous/detritivorous fish (common carp) together in order to cover all the food niches. In iAVs, the combination of these three species, or at least grass carp with common carp, would result in a better use of food, as the former would feed on both pellet and crop residues while the latter would also seek for wastes accumulating at the bottom of the tank. 

 

The supply of roots, among other crop residues, would be also extremely beneficial to the nutrient pool in the iAVs, because their digestion by the fish and the successive waste mineralization would return most of the micronutrients back to the plants. 

 

Other carp species (ornamental fish) 

Gold or Koi carps are mainly produced for the ornamental fish industry rather than food fish (Figure  7.8). 

 

These fish also have a high tolerance to a variety of water conditions and therefore are good candidates for an iAVs. They can be sold to individuals and aquarium stores for considerably more money than fish sold as food. 

 

Koi carps and other ornamental fish are a popular choice for vegetarian growers. Beyond the climatic characteristics and fish management issues, the choice of a carp species to be cultured in iAVs should follow a cost–benefit analysis that takes into account the convenience in culturing a fish that is bonier and generally fetches lower market prices than other species.

 

7.4.3 Catfish 

Main commercial types: 

Channel catfish (Ictalurus punctatus) 

African catfish (Clarias gariepinus)

 

Description 

 

Catfish are an extremely hardy group of fish tolerating wide swings in DO, temperature and pH (Figure 7.9). They are also resistant to many diseases and parasites, making them ideal for aquaculture. 

 

Catfish can be easily stocked at very high densities, up to 150 kg/m3 . These stocking densities require comprehensive mechanical filtration and solids removal beyond that discussed in this publication. 

 

The African catfish is one of many species in the Clariidae family. These species are air breathers, making them ideal for aquaculture as a sudden and dramatic drop in DO would not result in any fish mortalities.

 

 Catfish are the easiest species for beginners or those who want to grow fish in areas where the supply of electricity is not reliable. Given the high tolerance to low DO levels and high ammonia levels, catfish can be stocked at higher densities, provided there is adequate mechanical filtration. 

 

Regarding waste management, it is worth noting that suspended solid waste produced by catfish is less voluminous and more dissolved than that of tilapia, a factor that facilitates greater mineralization. 

 

Like tilapia, catfish grow best in warm water and prefer a temperature of 26 °C; but in the case of African catfish growth stops below 20–22 °C. 

 

The physiology of catfish is different from other fish, as they can tolerate high levels of ammonia, but, according to recent literature, nitrate concentrations of more than 100 mg/litre may reduce their appetite due to an internal regulatory control trigged by high levels of nitrate in their blood. 

 

Catfish are benthic fish, meaning they occupy only the bottom portion of the tank. This can cause difficulties in raising them at high densities because they do not spread out through the water column. In overcrowded tanks, catfish can hurt each other with their spines. When raising catfish, one option is to use a tank with greater horizontal space than vertical space, thereby allowing the fish to spread out along the bottom. 

Alternatively, many farmers raise catfish with another species of fish that utilize the upper portion of the tank, commonly bluegill sunfish, perch or tilapia. Catfish can be trained to eat floating pellets. 

 

7.4.4 Trout 

Main commercial type: 

Rainbow trout (Oncorhynchus mykiss)

 

Description 

 

Trout are carnivorous cold-water fish that belong to the salmon family (Figure 7.10). 

 

All trout require colder water than the other species previously mentioned, preferring 10–18 °C with an optimum temperature of 15 °C. Trout are ideal in Nordic or temperate climate regions, especially in winter. Growth rates significantly decrease as temperatures increase above 21 °C; above this temperature trout may not be able to properly utilize DO even if available. 

 

Trout require a high protein diet compared with carp and tilapia meaning greater amounts of nitrogen in the overall nutrient pool per unit of fish feed added. This occurrence allows for more cultivable areas of leafy vegetables while maintaining a balanced iAVs. 

 

Trout have a very high tolerance to salinity, and many varieties can survive in freshwater, brackish water and marine environments. Overall, trout require better water quality than tilapia or carp, particularly with regard to DO and ammonia. 

 

Successful aquaculture of trout also requires frequent water quality monitoring as well as backup systems for air and water pumps. Rainbow trout is the most common trout species grown in aquaculture systems in the United States of America and Canada and in sea cages or flow-through tanks and ponds in central or Northern Europe (Norway, Scotland [the United Kingdom]), in parts of South America (Chile, Peru), in many upland areas in tropical and subtropical Africa and Asia (Islamic Republic of Iran, Nepal, Japan) and Australia. 

 

Rainbow trout are long, thin and scale-less fish, usually blue-green and spotted on top with a red stripe on the sides. Trout are also cultured and released into streams and lakes to supplement sport fishing. 

Trout require a high-protein diet with substantial amount of fats. Trout are considered an “oily fish”, a nutritional description indicating a high amount of vitamin  A, vitamin D and omega-3 fatty acid, making them an excellent choice to grow for domestic consumption. Trout command higher prices in some markets for the same reason, but they require diets comparatively rich in fish oil.

 

7.4.5 Largemouth bass 

Main commercial type: 

Largemouth bass (Micropterus salmoides)

 

Description 

 

Largemouth bass are native to North America but are widely spread throughout the world, occurring in many water bodies and ponds (Figure 7.11). 

 

They belong to the order Perciformes (perch-like fish) which also includes striped bass, Australian bass, the black sea bass, the European sea bass and many others. 

 

Largemouth bass tolerates a wide temperature range as growth will only cease at less than 10 °C or more than 36 °C; they will stop feeding at temperatures less than 10 °C. The optimal growth temperatures are in the range of 24–30 °C for all fish stages. They tolerate low DO and pH, although for a good FCR the optimal DO is above 4 mg/litre. 

 

Largemouth bass prefer clean water with a concentration of suspended solids less than 25 mg/litre, yet growth has been observed in ponds with turbidity as high as 100 mg/ litre. As with trout, largemouth bass are carnivorous fish, demanding high protein diets; thus size cohorts should be separated to prevent the consumption of fry and very small juveniles by larger fish. 

 

Growth rates are highly dependent on temperature and quality of feed; in temperate climates most of the growth is obtained during the warmer seasons (late spring, summer and early fall). 

 

Given their high tolerance to DO as well as good resistance to high nitrite levels, largemouth bass are an excellent choice for farmers, particularly for those who cannot change species between cold and warm seasons. Attempts have been carried out to culture this species in polyculture with tilapia. 

 

Nutritionally speaking, largemouth bass contain relatively high levels of omega-3 fatty acids compared with other freshwater fish.

 

7.4.6 Prawns

SKIPPED

 

7.5 ACCLIMATIZING FISH 

 

Acclimatizing fish into new tanks can be a highly stressful process for fish, particularly the actual transport from one location to another in bags or small tanks (Figure 7.13).

 

 It is important to try to remove as many stressful factors as possible that can cause fatality in new fish. There are two main factors that cause stress when acclimatizing fish: changes in temperature and pH between the original water and new water; these must be kept to a minimum. 

 

The pH of the culture water and transport water should ideally be tested. If the pH values are more than 0.5 different, then the fish will need at least 24 hours to adjust. Keep the fish in a small aerated tank of their original water and slowly add water from the new tank over the course of a day. 

 

Even if the pH values of the two environments are fairly close, the fish still need to acclimatize. The best method to do this is to slowly allow the temperature to equilibrate by floating the sealed transportation bags containing the fish in the culture water. This should be done for at least 15 minutes. At this time small amounts of water should be added from the culture water to the transport water with the fish. Again, this should take at least 15 minutes so as to slowly acclimatize the fish. Finally, the fish can be added to the new tank.

 

7.6 FISH HEALTH AND DISEASE 

 

The most important way to maintain healthy fish in any aquaculture system is to monitor and observe them daily, noting their behaviour and physical appearance. Typically, this is done before, during and after feeding. 

 

Maintaining good water quality, including all the parameters discussed above, makes the fish more resistant to parasites and disease by allowing the fishes’ natural immune system to fight off infections. 

 

This section discusses briefly key aspects of fish heath, including practical methods to identify unhealthy fish and prevent fish disease. These key aspects are: 

  • Observe fish behaviour and appearance on a daily basis, noting any changes.
  • Understand the signs and symptoms of stress, disease and parasites.
  • Maintain a low-stress environment, with good and consistent water quality, specific to the species.
  • Use recommended feeding rates and do not overstock.

 

7.6.1 Fish health and well-being

The main indicator of fish well-being is their behaviour. In order to maintain healthy fish, it is important to recognize the behaviour of healthy fish as well as the signs of stress, disease and parasites. 

The best time to observe fish is during their daily feeding, both before and after adding the feed, and noting how much feed is eaten. 

 

Healthy fish exhibit the following behaviour:

  • Fins are extended, tails are straight.
  • Swimming in normal, graceful patterns is typical for many fish, and they do not exhibit lethargy. However, catfish often sleep on the bottom until they wake up and begin feeding.
  • Strong appetite and not shying away at the presence of the feeder.
  • No marks along the body. No discoloured blotches, streaks or lines.
  • No rubbing or scraping on the sides of the tank.
  • No breathing air from the surface.
  • Clear, sharp, shiny eyes.

 

7.6.2 Stress 

 

Stress has been mentioned several times throughout this publication and deserves special attention here.

 

Generally, stress is a physiological response of the fish when they live in less than optimal conditions. Overstocking, incorrect temperatures or pH, low DO and inappropriate feeding all cause stress (Table 7.2). 

 

The fishes’ bodies have to work harder to overcome these poor conditions, resulting in a depressed immune system. With a depressed immune system, the ability of the fish to heal and ward off disease is reduced. Stress can actually be measured in fish by monitoring certain hormones. 

 

Stress is an overall state of being, and stress alone does not kill the fish. However, if fish are stressed for an extended period, they will inevitably develop diseases from various bacteria, fungi and/or parasites. Avoid stress wherever possible, and realize that multiple factors can contribute to stress at the same time.

 

7.6.3 Fish disease 

 

Disease is always the result of an imbalance between the fish, the pathogen/causative agent and the environment. 

 

Weakness in the animal and a higher incidence of the pathogen in certain conditions cause disease. Sound fish management practices that build a healthy defence system are the primary actions to secure a healthy stock. Therefore, adequate environmental control is equally essential in order to avoid stress in fish and to reduce the incidence of pathogens. 

 

Diseases are caused from both abiotic and biotic factors. In previous chapters, water quality parameters have already been indicated as determinant factors to avoid metabolic disorders and mortality. In addition, control of climatic conditions as well as contaminants can offset many opportunistic infections and toxicity. 

 

The contained characteristics of recirculating systems make iAVs less prone to pathogen introductions and disease outbreaks because of better control of inputs and in the management of key water and environmental parameters.

 

In the case of incoming water from water bodies, the simple adoption of slow sand filtration can protect the iAVs from any possible parasite or bacteria introduction. 

 

Similarly, the elimination of snails and small crustaceans, as well as preventing the access or the contamination from animals and birds, can help offset the problems of parasites as well as possible bacterial contamination. 

 

The three major groups of pathogens that cause fish disease are fungus, bacteria and parasites. All of these pathogens can easily enter an aquaculture system from the environment, when adding new fish or new water, or could have previously existed in the unit. 

 

Prevention is by far the best way to prevent disease in fish. Daily observation of fish and monitoring for disease allows the disease, if present, to be treated quickly to prevent more fish from being infected (Figure 7.14). Treatment options for small-scale iAVs are limited. Prevent disease as much as possible.

 

Preventing disease 

 

The list below outlines some key actions for preventing disease and summarizes major lessons for growing fish in iAVs:

 

  • Obtain healthy fish seed from a reliable, reputable, and professional hatchery.
  • Never add unhealthy fish to the system. Examine new fish for signs of disease.
  • It is advisable in some cases to quarantine new fish in an isolation tank for 45 days before adding them to the main system. If possible and necessary, treat new fish with a salt bath (described below) to remove parasites or treat some early stage infections.
  • Ensure that the water source is from a reliable origin and use some sterilization method if it comes from a well or water bodies. Remove chlorine from water if it is from a municipal source.
  • Maintain key water quality parameters at optimum levels at all times.
  • Avoid sharp changes in pH, ammonia, DO, and temperature.
  • Ensure adequate biofilter size to prevent ammonia or nitrite accumulation.
  • Ensure adequate aeration to keep DO levels as high as possible.
  • Feed the fish a balanced and nutritious diet.
  • Keep the fish feed in a cool, dry, and dark place to prevent it from molding.
  • Make sure that live food sources are pathogen-free and parasite-free. Feed that is not from a verifiable origin should be pasteurized or sterilized.
  • Remove uneaten feed and any source of organic pollution from the tank.
  • Make sure the fish tank is shaded from direct sunlight, but not in complete darkness.
  • Prevent access of birds, snails, amphibians, and rodents that can be vectors of pathogens or parasites.
  • Do not allow pets or any domestic animals to access the production area.
  • Follow standard hygiene procedures by washing hands, cleaning/sterilizing gear.
  • Do not allow visitors to touch the water or handle fish without following proper hygiene procedures.
  • Use one fish net for each fish tank to prevent cross-contamination of diseases or parasites.
  • Avoid loud noise, flickering lights, or vibration near the fish tank.

 

Recognizing disease 

 

Diseases may occur even with all the prevention techniques listed above. It is important to stay vigilant and monitor and observe fish behaviour daily to recognize the diseases early. 

 

The following lists outline common physical and behavioural symptoms of diseases. For a more detailed list of symptoms and more specific remedies please refer to Appendix 3.

 

External signs of disease:
  • ulcers on body surface, discoloured patches, white or black spots
  • ragged fins, exposed fin rays
  • gill and fin necrosis and decay
  • abnormal body configuration, twisted spine, deformed Kaws
  • extended abdomen, swollen appearance
  • cotton-like lesions on the body
  • swollen, popped-out eyes (exophthalmia)
Behavioural signs of disease:
  • poor appetite, changes in feeding habits
  • lethargy, different swimming patterns, listlessness
  • odd position in water, head or tail down, difficulty maintaining buoyancy
  • fish gasping at the surface
  • fish rubbing or scraping against objects
Abiotic diseases 

 

Most of the mortalities in iAVs are not caused by pathogens, but rather by abiotic causes mainly related to water quality or toxicity. Nevertheless, such agents can induce opportunistic infections that can easily occur in unhealthy or stressed fish. 

 

The identification of these causes can also help the aquaponic farmer to distinguish between metabolic and pathogenic diseases and lead to prompt identification of the causes and remedies. Appendix 3 contains a list of the most common abiotic diseases and their symptoms.

 

Biotic diseases 

 

In general, iAVs and recirculating systems are less affected than pond or cage aquaculture farming by pathogens. In most cases, pathogens are actually already present in the system, but disease does not occur because the fishes’ immune system is resisting infection and the environment is unfavourable for the pathogen to thrive. 

 

Healthy management, stress avoidance and quality control of water are thus necessary to minimize any disease incidence. 

 

Whenever disease occurs, it is important to isolate or eliminate the infected fish from the rest of the stock and implement strategies to prevent any transmission risk to the rest of the stock. If any cure is put into action, it is fundamental that the fish be treated in a quarantine tank, and that any products used are not introduced into the iAVs. This is in order to avoid any unpredictable consequences to the beneficial bacteria. 

 

Appendix 3 indicates some of the most common biotic diseases occurring in fish farming and the remedies normally adopted. More details are available from the literature and from local fishery extension services.

 

Treating disease I

 

If a significant percentage of fish are showing signs of disease, it is likely that the environmental conditions are causing stress. In these cases, check levels of ammonia, nitrite, nitrate, pH and temperature, and respond accordingly. If only a few fish are affected, it is important to remove the infected fish immediately in order to prevent any spread of the disease to other fish.

 

Once removed, inspect the fish carefully and attempt to determine the specific disease/cause. Use this publication as a starting guide and then refer to outside literature. However, it may be necessary to have a professional diagnosis carried out by a veterinarian, extension agent or other aquaculture expert. 

 

Knowing the specific disease helps to determine the treatment options. Place the affected fish in a separate tank, sometimes called a quarantine or hospital tank, for further observation. Kill and dispose of the fish, as appropriate. 

 

Disease treatment options in small-scale iAVs are limited. Commercial drugs can be expensive and/or difficult to procure. Moreover, antibacterial and antiparasite treatments have detrimental effects on the rest of the system, including the biofilter and plants. If treatment is absolutely necessary, it should be done in a hospital tank only; antibacterial chemicals should never be added to an iAVs. 

 

One effective treatment options against some of the most common bacterial and parasite infections is a salt bath. 

 

Salt bath treatment 

 

Fish affected with some ectoparasites, moulds and bacterial gill contamination can benefit from salt bath treatment. Infected fish can be removed from the main fish tank and placed into a salt bath. This salt bath is toxic to the pathogens, but non-fatal to the fish. 

 

The salt concentration for the bath should be 1 kg of salt per 100 litres of water. Affected fish should be placed in this salty solution for 20–30 minutes, and then moved to a second isolation tank containing 1–2 g of salt per litre of water for another 5–7 days. 

 

In bad white-spot infections, all fish may need to be removed from the iAVs and treated this way for at least a week. During this time, any emerging parasites in the iAVs will fail to find a host and eventually die. The heating of the water in the iAVs can also shorten the parasite life cycle and make the salt treatment more effective. 

 

Do not use any of the salt bath water when moving the fish back into the iAVs because the salt concentrations would negatively affect the cultured plants. 

 

7.7  Fish Harvesting in iAVs

 

Harvesting Stages

Fish can be harvested at various stages of their growth, depending on the intended use. Some common harvesting sizes include:

  1. Small-sized fish (100g and beyond): These fish can be incorporated into a menu, but it is often more practical to grow them out further.
  2. Plate-sized fish (250g to 400g): This size range is suitable for serving whole fish on a plate.
  3. Fillets (12 months and beyond): For obtaining fillets, fish can be grown out for 12 months or more.

In iAVs, the harvesting size and time depend on the specific goals and requirements of the system.

 

7.8 PRODUCT QUALITY 

 

In cultured fish, particularly freshwater species, there is often the risk of off-flavour. In general, this reduction in flesh quality is due to the presence of specific compounds, the most common of which are geosmin and 2-methylisoborneol. 

 

These secondary metabolites, which accumulate in the lipid tissue of fish, are produced by the bluegreen algae (cyanobacteria) or by the bacteria of the genus Streptomyces, actinomycetes and myxobacteria. Geosmin gives a clear muddy flavour, while 2-methylisoborneol gives a mildewed taste that can severely affect consumer acceptance and disrupt the marketability of the product. 

 

Off-flavour occurs in both earthen ponds and RASs. A common remedy for off-flavours consists of purging the fish for 3–5  days in clean water before sale or consumption. Fish must starve and be kept in a separated and aerated tank. In iAVs, this process can be easily integrated in the ordinary management as the water used for the purging can be eventually used to refill the system.

 

7.9 CHAPTER SUMMARY

  • Standard manufactured fish feed pellets are recommended for use in iAVs because they are a whole feed containing the correct balance of proteins, carbohydrates, fats, vitamins, and minerals needed for fish.
  • Protein is the most important component for building fish body mass. Omnivorous fish such as tilapia and common carp need about 32 percent protein in their diet, carnivorous fish need more.
  • Never overfeed the fish, and remove uneaten food after 30 minutes 15 OR 30?to reduce risks of ammonia or hydrogen sulphide toxicity.
  • Water quality needs to be maintained for fish. Ammonia and nitrite must be close to 0 mg/litre as they are toxic at any detectable levels. Nitrate should be less than 400 mg/litre. DO should be 4–8 mg/litre.
  • Tilapia, carp, and catfish are highly suitable for iAVs in tropical or arid conditions as they grow quickly and can survive in poor quality water and at lower DO levels. Trout grow well in cold water, but require better water quality.
  • Fish health should be monitored daily, and stress should be minimized. Poor and/or changing water quality, overcrowding, and physical disturbance can cause stress, which may lead to disease outbreaks.
  • Abnormalities or changes in physical behaviour can indicate stress, bad water quality, parasites, or disease. Take the time to observe and monitor the fish in order to recognize symptoms early and provide treatment.

8. Management and troubleshooting

 

The previous chapters focused on the importance of bacteria to ensure good growth of both plants and fish, on the key factors when building an iAVs, and how to properly care for both microbes, fish and plants in a symbiotic ecosystem. 

 

This chapter summarizes the main principles and “rules of thumb” to provide a reference on the optimal fish-to-plant ratio, feeding regime and biofilter sizing. The second section of this chapter lists all the important management phases from starting a unit to production management over an entire growing season. 

 

There is also an in-depth discussion regarding the management of fish and plants during the first three months of production. Finally, this chapter sets out practical daily, weekly and monthly checklists for managing a unit over a growing season, and what to do if problems arise. 

 

8.1 COMPONENT CALCULATIONS AND RATIOS 

 

iAVs is a balanced ecosystem. The fish (and thus, fish feed) supply adequate nutrients for the plants; the plants need to filter the water for the fish. 

 

The biofilter needs to be large enough to process all the fish wastes. This section provides helpful calculations to estimate the sizes of each of the components. 

 

8.1.1 Plant growing area, amount of fish feed and amount of fish 

 

The most successful way to balance an iAVa is to use the feed rate ratio described in Section 2.1.4. This ratio is important so that the fish and plants can thrive symbiotically within the ecosystem. The ratio estimates how much fish feed should be added each day to the system, and it is calculated based on the area available for plant growth. 

 

This ratio depends on the type of plant being grown; fruiting vegetables require about one-third more nutrients than leafy greens to support flowers and fruit development. The type of feed also influences the feed rate ratio, and all calculations provided here assume an industry standard fish feed with 32 percent protein. 

 

ADD A SECTION ABOUT NUTRIENT EQUIVALENCY

 

ADD NOTE THAT FRUIT AND VEGETABLES SHOULD BOTH BE GROWN TO ENSURE A WIDE SPECTRUM NUTRIENT REMOVAL

 

The recommended first step in the calculation is to determine how many plants are desired. These figures are only averages, and many variables exist depending on plant type and harvest size, and therefore should only be used as guidelines. ADD LINK OR ADD TO RECOMMENDED READING HORTICULTURE BOOKS OR GUIDES ABOUT PLANT SPACING

 

Once the desired number of plants has been chosen, it is then possible to determine the amount of growing area needed and, consequently, the amount of fish feed that should be added to the system every day can be determined. 

REMOVE THIS AND REPLACE WITH IAVS GUIDE

 

Once the amounts of growing area and fish feed have been calculated, it is possible to determine the biomass of the fish needed to eat this fish feed. 

 

Different-sized fish have different feed requirements and regimes, this means that many small fish eat as much as a few large fish. In terms of balancing an iAVs, the actual number of fish is not as important as the total biomass of fish in the tank. 

 

On average, for the species discussed in Section 7.4, the fish will consume 1–2 percent of their body weight per day during the grow-out stage. This assumes that the fish are larger than 50 g because small fish eat more than large ones, as a percentage of body weight. CHANGE THIS AS I THINK IT IS INCORRECT

 

AT WHAT SIZE???!

 

The example below demonstrates how to conduct this set of calculations, determining that, in order to produce 25 heads of lettuce per week, an aquaponic system should have 10–20 kg of fish, fed 200 grams of feed per day, and have a growing area of 4 m2 . The calculations are as follows:

 

Although extremely helpful, this feed ratio is really only a guide, particularly for small-scale units. There are many variables involved with this ratio, including the size and type of fish, water temperature, protein content of the feed and nutrient demands of the plants, which may change significantly over a growing season. These changes may require the farmer to adjust the feeding rate.

 

Monitoring the plants helps to determine if the system remains in balance. If deficiencies are noticed, then slowly increase the feed rate per day without overfeeding the fish. 

8.1.2 Water volume 

 

Different stocking densities affect fish growth and health, and are one of the most common root causes for fish stress. 

 

The small-scale units described in this publication have about 1,000 litres of water and should contain 80-100 Tilapia fingerlings at 10 grams in size. New iAVs farmers are strongly recommended to follow these guidelines. 

 

For reference, an average tilapia weighs 250 g at harvest size. REMOVE – CHANGE – EDIT 

 

8.1.3 Filtration requirements – biofilter 

 

Appendix  4 contains more information on sizing biofilters and calculating the volume required.

 

8.1.4 Summary of component calculations

 

  • The feed rate ratio provides a way to balance the components of an iAVs, and to calculate planting area, fish feed, and fish biomass.

 

  • Fish feeding rate: 1-2 percent of their body weight per day.

  • Biofiler Ratio

Table 8.1 summarizes the key figures and ratios for designing a small-scale iAVs. It is important to be aware that the figures are just guides as other external factors (e.g. climate conditions, access to a constant supply of electricity) may change the design on the ground. REMOVE THE TABLE?

8.1.4  Sand Testing

 

Performing the Differential Settling Test and Determining Soil Composition

The Differential Settling Test is a method used to determine the relative proportions of sand, silt, and clay in a soil sample. This information is crucial for understanding soil texture and its suitability for various applications, such as agriculture or construction. The test involves the following steps:

  1. Collect a soil sample and place it in a jar, then add distilled water.
  2. Shake the jar for a few minutes to mix the soil and water thoroughly, then let it sit undisturbed for 24 hours.
  3. After 24 hours, measure the total depth of the settled soil using a metric ruler.
  4. Shake the jar again for a few minutes, then let it stand for 30 seconds to allow the sand to settle. Measure the depth of the settled sand and record it as the sand depth.
  5. Without shaking the jar, let it stand for another 30 minutes. Measure the depth of the settled silt by subtracting the sand depth from the total depth, and record it as the silt depth.
  6. Shake the jar once more and let it sit for three hours. Calculate the clay depth by subtracting the silt and sand depths from the total depth.

Once you have the depths of sand, silt, and clay, you can calculate the percentages of each component in the soil sample using the following formulas:

  • % Sand = (Sand Depth / Total Depth) x 100
  • % Silt = (Silt Depth / Total Depth) x 100
  • % Clay = (Clay Depth / Total Depth) x 100

8.1.5 Understanding Pore Space Volume in iAVs

The concept of Pore Space Volume is crucial in iAVs. It refers to the volume of space between individual sand particles, which can be filled with either air or water. This space plays a significant role in the functioning of iAVs, affecting water flow, nutrient cycling, and the overall health of the system.

Role of Pore Space Volume

The Pore Space Volume determines the amount of water that can flow through or be held within the sand. This, in turn, influences the environment for microbes and the rhizosphere, providing them with a suitable habitat for growth and efficient nutrient cycling. The balance of air and water within these spaces is critical for the thriving of iAVs, contributing to improved soil fertility, increased crop yields, and reduced pollution levels.

Measuring Pore Space Volume

To measure the Pore Space Volume, a simple method involving two one-litre jugs is used. One jug is filled with sand, and the other with water. Water is then gradually added to the sand until it becomes saturated, with the volume of water added being carefully tracked.

Impact of Pore Space Volume

Dry sand of the correct particle size range typically has a Pore Space Volume of around 25% – 30%. This volume is crucial as it can impact the efficiency of an iAVs. If the Pore Space Volume is too low, the sand particles may be too small, potentially limiting the ability of water to drain away. Conversely, if the Pore Space Volume is too high, the particles may be too large, causing the water to drain away too quickly.

The Pore Space Volume also affects the biofilm and microbes by providing a place for them to live. Oxygen is essential for microbial life, so having an adequate amount of oxygen in the pore spaces is important. The presence of fresh atmospheric oxygen helps replace stale gases that may have built up within the pores, which can be harmful to microorganisms living there.

Changes in Pore Space Volume

It’s important to note that sand will continue to settle the first few times that it is flooded and drained. As a result, the Pore Space Volume will diminish initially and then stabilise. If the initial Pore Space Volume is marginal, future flood and drain events could negatively impact drainage.

8.1.6 Sand Hydraulic Conductivity in iAVs

 

Importance of Hydraulic Conductivity

Hydraulic conductivity is a crucial factor in iAVs, as it measures the ease with which water can pass through sand. High hydraulic conductivity indicates that water can easily flow through the sand, while low hydraulic conductivity means water flow is more restricted. Understanding the hydraulic conductivity of sand is essential for determining its suitability in an iAVs system.

Flood and Drain Cycle

The flood and drain cycle is a critical component of iAVs, as it provides the necessary moist environment for plants and microbes while ensuring an oxygen-rich air supply. 

This cycle involves alternating between flooding the system with water and draining it out. Maintaining the proper balance between water and air in the sand bed is crucial for supporting plant growth and microbial life.

Oxygen Supply

A sufficient oxygen supply is vital for both plants and microbes in iAVs. Plants use oxygen during photosynthesis to convert light energy into chemical energy, while microbes rely on oxygen to break down organic matter in the soil. 

If the system becomes anaerobic due to prolonged flooding, oxygen levels will be depleted, leading to decreased microbial activity and reduced plant growth.

Measuring Hydraulic Conductivity

To measure hydraulic conductivity, a DIY device called a percolation rate tester is used. This tester helps confirm the accuracy of the pore volume space, which is directly related to the amount of oxygen that can reach soil microbes. If sand particles are too small, they can clog the pores and prevent oxygen from reaching the microbes, leading to poor microbial activity.

Sand Selection

Selecting the right sand for iAVs is crucial for ensuring proper hydraulic conductivity. The sand must be inert, free of silt or clay, and drain effectively. Crystalline quartz, granite, and rounded sand are suitable options, while sandstone, beach sand, and flat or flaky sand should be avoided.

8.1.7 Moisture Management in Integrated AquaVegeculture Systems (iAVs)

 

Understanding Water Retention

Water retention is the capacity of a substance, in this case sand, to hold water. This is a crucial aspect of iAVs as it determines the amount of water the sand can retain, which in turn affects the hydration of the plants. Insufficient water retention can hinder plant growth. Therefore, assessing the water retention of the sand is a vital step in establishing an iAVs. This is achieved by measuring the amount of water the sand can hold.

Role of Biofilm in Water Retention

In a mature iAVs system, sand grains are coated with a biofilm, a layer of bacteria and other microorganisms that adhere to the sand’s surface. This biofilm enhances water retention by holding additional moisture. Some microbes can also store water within their cells, which is then released upon their death or consumption by other microbes.

Pore Space and Hydrostatic Tension

Despite appearing solid, dry sand is approximately 25% to 30% air by volume. It’s crucial to note that a certain amount of water remains in the sand after the drain cycle, available to the plants until the next flood cycle. This water is bound to the sand particles by hydrostatic tension, a force that holds water to the sand particles’ surface. This tension is created when a particle submerged in water forms an invisible film around itself due to surface tension, acting as a barrier between air and water molecules and causing them to form an adhesive bond on the particle’s surface.

Water Retention Variations

The amount of water retained in the sand varies according to the time elapsed from the last flood cycle. For instance, about 5% of the water pumped may be retained after the first flood cycle in the morning, after an 8-hour break, whereas only 1% may be retained immediately after subsequent flood cycles throughout the day, approximately two hours apart. These figures are not fixed and may vary from situation to situation. They serve to illustrate the dynamic relationship between sand and water in the system.

Testing Water Retention

To determine the water retention of a sand sample, the hydraulic conductivity test should be repeated several times, measuring the amount of water that drains from the sand after each flood cycle. After the sand is initially flooded with water, a certain amount will remain in the sand. This retained water can vary depending on the time since the last flood cycle.

 

8.2 NEW AQUAPONIC SYSTEMS AND INITIAL MANAGEMENT 

8.2.1 Building and preparing the unit 

Detailed step-by-step building instructions are provided in Appendix  8. Once the unit is complete, it is time to prepare the system for routine function. 

Although aquaponic unit management does not require excessive time and effort, it is important to remember that a well-functioning system requires a minimum of 10–20  minutes of maintenance every day. Before stocking a new system with fish and planting the vegetables, it is crucial to ensure that all of the equipment is working properly. The most important aspects to check are the water pump, the air pump and water heaters (where applicable). It is essential to check that the NFT pipes and media beds are steady and balanced horizontally. 

Start running water in the system and make sure that there are no leaks or loose plumbing connections. If there are, tighten or fix them immediately. Section 9.3 provides further methods to secure the water levels and prevent catastrophic loss-of-water events. Once built, cycle the water for at least two days in order to let any chlorine dissipate. This process can be accelerated using heavy aeration. This is not necessary where the source water contains no chlorine, such as rainwater or filtered water.

Media bed unit preparation 

The growing medium (volcanic gravel, expanded clay) should be well washed. Fill the beds with the medium and let the water run through it; the water should be clear. Remove any sedimentation (if present) by flushing out the beds with water. If using an electric timer to flood and drain the beds, it is important to synchronize the time it takes to fill the growing beds and the flow rate of the water entering the bed. If using a bell siphon, the water flow rate should be adjusted to ensure the auto siphon function. The water flow rate must be enough to activate the siphon, but not so strong that it prevents the suction from stopping.

8.2.2 System cycling and establishing the biofilter 

Once the unit has passed the initial component checks and has been running for 2–3 days with no problems, it is time to cycle the unit. 

As discussed in Chapter  5, system cycling is the term that describes the initial process of building a bacterial colony in a new aquaponic unit. Normally, this is a 3–6 week process that involves introducing an ammonia source in the unit to feed the nitrifying bacteria and help them proliferate. The steps involved have been outlined in Chapter 5 and they should be followed for every new unit. 

During the cycling process, it is vital to test ammonia, nitrite and nitrate levels every 3–5 days to make sure the ammonia concentrations do not become harmful for bacteria (> 4 mg/litre). If they do, a water change is necessary. The unit has completed the cycling process when nitrate levels begin to rise and ammonia and nitrite levels fall close to zero. 

8.3 MANAGEMENT PRACTICES FOR PLANTS 

Seedlings can be planted into the system as soon as nitrates are detected. Expect these first plants to grow slowly and exhibit some temporary deficiencies because the nutrient supply in the water is temporarily small. It is recommended to wait 3–4 weeks to allow the nutrients to accrue. In general, aquaponic systems show a slightly lower growth rate than soil or hydroponic production in the first six weeks. 

However, once a sufficient nutrient base has been built within the unit (1–3 months) the plant growth rates become 2–3 times faster than in soil.

8.3.1 Review of planting guidelines 

Plant selection

It is best to start a new aquaponic system with fast-growing robust plants with a low nutrient demand. Some examples are leafy green vegetables, such as salads, or nitrogenfixing plants, such as beans or peas. 

 

After 2–3 months, the system is ready for larger fruiting vegetables that demand a greater amount of nutrients.

 

Plant spacing 

 

Seedlings can be planted using a slightly denser spacing than for most vegetables in soil because in aquaponics the plants do not compete for water and nutrients. 

 

Even so, the plants still need enough room to reach their mature size and to avoid reciprocal competition for light, which would depress their marketable quality or favour vegetative growth instead of fruits. 

 

In addition, consider shading effects of the full-grown plants, which allows for the contemporary cropping of shade-tolerant species next to taller plants.

 

Supplementing iron 

 

Some new aquaponic units experience iron deficiencies in the first 2–3  months of growing as iron is important during the early stages of plant growth and is not abundant in fish feed. Thus, it may be necessary to initially add chelated iron (soluble iron in powder form) to the unit to meet the requirements for plants. The recommendation is to add 1–2 mg/litre for the first 3 months of starting a unit, and again when iron deficiencies are present. Chelated iron can be bought from agricultural suppliers in powder form. Iron can also be supplemented by using aquaponics-safe organic fertilizers such as compost or seaweed tea, as iron is abundant in both. Section 9.1.1 discusses aquaponics-safe organic fertilizers.  MOST LIKELY REMOVE TIS BUT CONFIRM AGAINST THE RESEARCH WHAT THE IRON LEVELS WERE…OR MORE TO THE POINT, SEE IF THEY WEE DEFICIENT

 

8.3.2 Establishing a plant nursery 

 

Vegetables are the most important output for small-scale aquaponic production. 

 

It is essential that only strong healthy seedlings are planted. Moreover, the planting methods applied must avoid transplant shock as much as possible. 

 

Thus, the recommendation is to establish a simple plant nursery to ensure an adequate supply of healthy seedlings ready to be planted into the aquaponic units. It is always best to have an excess of plants ready to go into the system, and often waiting for seedlings is a source of production delay. 

 

A simple nursery bed can be constructed using horizontal wood lengths lined with polyethylene liner, as shown in Figure 8.2. 

Water is pumped into the bed for about half an hour each day (controlled by a simple electric timer), allowing water and moisture to soak into the growing media. The water is then slowly drained down into a tank below. This cycle is repeated daily in order to prevent water logging of the seedlings. 

 

Too much moisture increases the threat of fungal infections. Polystyrene propagation trays are placed into the nursery bed and are filled with soil, inert grow media such as rockwool, peat, coco fibre, vermiculite, perlite or a potting mix with a combination of the various types of growing medium. 

 

Simpler alternatives for propagation trays are also possible using recyclable materials such as empty egg boxes (Figure 8.3). Choose propagation trays that allow adequate distance between seedlings in order to favour good growth without competition for light. 

 

Box 4 lists seven steps for sowing seeds.

 

Direct seeding in media beds 

It is possible to sow seeds straight into the media bed. 

 

If using a flood-anddrain mechanism (e.g. bell siphon) the seeds may be washed around. Therefore, the siphon should be removed while sowing seeds in the bed, and then replaced when the first leaves begin to appear. 

 

8.3.3 Transplanting seedlings 

 

Transplanting seedlings obtained from soil beds is not recommended; it should only be done if strictly necessary. In this case, all of the soil needs to be washed out from the root system very gently because it may carry plant pathogens. 

 

This washing process is very stressful for seedlings and it is possible to lose 4–5 days of growth as the plant adjusts to new conditions. 

 

Thus, it is preferable to start seeds using inert media (rockwool, vermiculite or coco fibre) in propagation trays as explained above. In this way, the seedlings can be transplanted with minimal shock. Larger plants from pots can also be planted, although again the soil needs to be removed. 

 

Avoid transplanting in the middle of the day because plant roots are extremely sensitive to direct sun light and leaves can face water stress due to the new growing conditions. It is recommended to plant at dusk so the young seedlings have a night to acclimatize to their new environment before the morning sun.

 

Media bed planting 

 

When planting in volcanic gravel or any other growing media recommended in Chapter 6, simply push aside the gravel and dig a hole that is big enough to contain the plant. 

 

Plant at the highest point of flooding in the media bed (about 5–7 cm below the surface of the gravel) so the roots are partially submerged in water. 

Do not plant too deeply, which would allow water to contact the stem or leaves and could lead to disease (collar rot).

 

8.3.4 Harvesting plants 

 

In 1–2 months, leafy green vegetables should be ready to harvest. 

 

After three months, the unit should also have enough of a nutrient base to begin planting larger fruiting vegetables. 

The following points below detail the final guidelines for growing plants after the initial three-month period.

 

Staggered planting and harvesting 

 

As discussed in Chapter 6, it is worth staggering the planting over time in order to prevent harvesting the entire crop all at once. If this were to happen, nutrient levels would decrease just before harvest, which might create nutritional problems for the plants, and spike after the harvest, which would stress the fish. 

 

Moreover, staggered planting allows for continual harvest and transplant of vegetables and ensures constant nutrient uptake and water filtration.

 

Harvesting approaches 

 

When harvesting full plants from media beds (i.e. lettuce), make sure the entire root system is removed. 

 

In addition, shake the gravel stuck in between the roots and place the gravel back in the media bed. In NFT and DWC pipes/canals also make sure the whole root system is removed (Figure  8.9). 

 

Place the discarded plant roots into a compost bin to recycle the plant waste. Leaving roots and leaves in the system can encourage disease. When harvesting vegetables use a sharp clean knife. 

 

To prevent any bacteria contamination, ensure that aquaponic water does not wet the leaves. Place harvested plants into a clean bag and wash and chill the crops as soon as possible to maintain freshness.

 

8.3.5 Managing plants in mature systems 

 

Stabilizing pH 

 

It is vital for good plant growth to maintain the pH between 6 and 7, so plants have access to all the nutrients available in the water. 

 

Add small amounts of base or buffer whenever the pH approaches 6.0 in order to maintain optimum pH levels as described in Section 3.6. 

 

Add rainwater or correct with acid any alkalinity-rich water only if the hardness level in the aquaponic system is too high to prevent nitrifying bacteria from naturally lowering the pH to optimal levels. 

 

Treat the water with acid outside the aquaponic system, and pour the water into the system after checking the pH. 

 

Organic fertilizers 

 

If deficiencies do occur, it is necessary to add outside nutrients. 

 

Organic liquid fertilizer can be used as either diluted foliar feed for plant leaves or poured straight into the root zone. 

 

Chapter 9 discuses methods to produce simple home-made fertilizers that are aquaponic-safe. Compost tea and seaweed tea are recommended. 

 

Deficiencies are discussed in Section 6.2.3. 

 

Deficiencies often occur when there are too many plants for the number of fish, or when feeding is reduced during winter months. 

 

Before adding fertilizers, be sure to check pH to make sure there is no nutrient lockout. 

 

Pests and disease 

 

Be sure to try to prevent pests using the IPPM techniques discussed in Section  6.5. If pests remain a problem, begin by using the mechanical removal techniques before considering sprays. 

 

Only use aquaponic-safe remedies, such as: plant extracts or repellents, biological insecticides (Bacillus thuringiensis and Beauveria bassiana), soft soaps, ash, plant oils or extracts of essential oils, chromatic/attractant traps, and external attractant plants treated with insecticides. Regardless, avoid letting the spray enter the water.

 

Follow seasonal planting advice 

 

To an extent, aquaponic food production methods provide a means to extend planting seasons, particularly if the unit is housed inside a greenhouse. 

 

However, it is still strongly recommended to follow local seasonal planting advice. Plants grow better in the season and environmental conditions to which they are adapted. 

 

8.3.6 Plants – summary

 

  • Use plants with low nutrient demands for the first few months, i.e. lettuce and beans/peas.
  • Plants with high nutrient demands can be planted after the first 3-4 months.
  • Use plants recommended for aquaponics, and follow seasonal planting guides for the location.
  • Establish a plant nursery to ensure adequate numbers of healthy seedlings.
  • Transplant adequately grown and strong seedlings that have a well-developed root system.
  • Gently remove excess substrate from the roots before planting into the system.
  • Leave sufficient spacing in between plants according to their size when mature.
  • Plan a staggered harvesting system.
  • Organic fertilizers may be necessary if deficiencies occur.
  • Maintain appropriate water quality, especially a pH of 6-7.

 

8.4 MANAGEMENT PRACTICES FOR FISH 

 

Adding fish to a new aquaponic unit is an important event. It is best to wait until the initial cycling process is totally completed and the biofilter is fully functioning. 

 

Ideally, the ammonia and nitrite are at zero and nitrates are beginning to rise. This is the safest time to add fish. If it is decided to add fish before cycling, then a reduced number of fish should be added. This time will be very stressful for the fish, and water changes may be necessary. 

 

Cycling the system with fish can actually take longer than fish-less cycling. The fish must be properly acclimatized to the new water. 

 

Be sure to match the temperature and pH, and always acclimatize the fish slowly (as described in Section 7.5). When purchasing fingerlings from a local hatchery, make sure the fish are healthy and check carefully for any signs of disease.

 

8.4.1 Fish feeding and growth rates 

 

The method of calculating the fish feed using the feed rate ratio applies to mature systems during the grow-out stage of the fish and needs further consideration here. Using the same example from Section 8.1.1, the target biomass for a 1 000 litre tank is 10–20  kg. This would be about 40  harvest-size tilapia. However, during the first 2–3 months, the fish are small and do not eat as much as was calculated (200 g of feed per day) to supply nutrients for the whole grow bed. 

 

More specifically, newly stocked fingerling-sized fish weigh about 50 grams. Juvenile fish can be fed about 3 percent of their body weight per day. Therefore, an initial stocking of 40 fingerlings would weigh 2 000 g, and together they would eat approximately 60 g of fish feed per day. A low initial stocking density is a good practice for immature aquaponic systems because it gives the biofilter additional time to develop and allows the plants time to grow and filter more nitrate.

 

The recommendation is to estimate feeding based on body weight, but to carefully monitor feeding behaviour and adjust the ration accordingly. As the fish grow, they begin to eat more food. 

 

Moreover, it is recommended to provide a diet comparatively richer in protein to juvenile fish, if different feeds formulations are available and feasible. After 2–3 months feeding at this rate, the 40 fish will have grown to 80–100 grams each and weigh a total of 3  200–4  000  g. At this point, they should be able to eat 80–100 g of feed per day, which is still only half of that calculated by the feed rate ratio in the earlier example. 

 

Continue to feed the fish as much as they will eat, but increase the ration slowly to prevent wasted food. 

 

Within a few more months, these same fish will each weigh 500 g with a total biomass of 20 000 grams and eat 200 g of fish feed per day. For tilapia grown in good water quality at 25 °C, it takes 6–8 months to grow from as stocking size of 50 g to a harvest size of 500 g. Make sure to divide the feeding into morning and afternoon rations. 

 

Moreover, juvenile fish benefit from an additional lunch-time feeding. Splitting the ration is healthier for the fish and also healthier for the plants, providing an even distribution of nutrients throughout the day. 

 

Spread the feed across the entire surface of the water so  all the fish can eat without injuring one another or hitting the side of the tank. Avoid scaring the fish during feeding by refraining from sudden movements.

 

Stand still and observe the fish. Always remove any uneaten fish food after 30 minutes, and adjust the next feeding ration accordingly. If there is no food left after 30 minutes, increase the ration; if there is a lot left, decrease the ration. 

 

A major indicator of healthy fish is a good appetite, so it is important to observe their general feeding behaviour. If their appetite declines, or if they stop feeding altogether, this is a major sign that something is wrong with the unit (most probably poor water quality). 

 

Moreover, fish appetite is directly related to water temperature, particularly for tropical fish such as tilapia, so remember to adjust or even stop feeding during colder winter months

 

8.4.2 Harvesting and staggered stocking 

 

A constant biomass of fish in the tanks ensures a constant supply of nutrients to the plants. 

 

This ensures that the fish eat the amount of feed calculated using the feed rate ratio. The previous example shows how the feeding ration depends on the size of the fish, and small fish are not be able to eat enough feed to supply the full growing area with adequate nutrients. 

 

To achieve a constant biomass in the fish tanks, a staggered stocking method should be adopted. This technique involves maintaining three age classes, or cohorts, within the same tank. 

 

Approximately every three months, the mature fish (500 g each) are harvested and immediately restocked with new fingerlings (50 g each). This method avoids harvesting all the fish at once, and instead retains a more consistent biomass. 

 

Table 8.2 outlines the potential growth rates of tilapia in one tank over a year using the staggered stocking method. 

 

The important aspect of this table is that the total weight of the fish varies between 10–25 kg, with an average biomass of 17 kg. This table is a basic guideline depicting optimum conditions for fish growth. In reality factors such as water temperature and stressful environments for fish will distort the figures presented here.

 

Table 8.2: Notes: Fingerling tilapia (1.5  kg = 50  g/fish × 30  fish) are stocked every three months. Each fish survives and grows to harvest size (15 kg =  500 g/fish × 30 fish) in six months. The asterisk indicates harvest. The range during harvest/stocking months accounts for the range if not all 30 fish are taken at once, i.e. the 30 mature fish are harvested throughout the month. This table serves only as a theoretical guide to illustrate staggered harvest and stocking in ideal conditions

 

If it is not possible to obtain fingerlings regularly, an aquaponic system can be still managed by stocking a higher number of juvenile fish and by progressively harvesting them during the season to maintain a stable biomass to fertilize the plants. 

 

Table 8.3 shows the case of a system stocked every six months with tilapia fingerlings of 50 g. 

 

Table 8.3: Notes: Tilapia fingerling are stocked every six months. Staggered harvest starts from the third month to keep the total fish below the maximum stocking biomass of 20 kg/m3 . The table shows the theoretical weight of each batch of harvested fish along the year if fish are reared in ideal conditions.

 

In this case, the first harvest starts from the third month onward. 

 

Various combinations in stocking frequency, fish number and weight can apply, providing that fish biomass stands below the maximum limit of 20 kg/m3 . 

 

If the fish are mixed-sex, the harvest must firstly target the females to avoid breeding when they reach sexual maturity from the age of five months. 

 

Breeding depresses the whole cohort. In the case of mixed-sex tilapia, fish can be initially stocked in a cage and males can then be left free in the tank after sex determination. Remember that adult tilapia, catfish and trout will predate their smaller siblings if they are stocked together. A technique to keep all of these fish safely in the same fish tank is to isolate the smaller ones in a floating frame. This frame is essentially a floating cage, which can be constructed as a cube with PVC pipe used as frame and covered with plastic mesh. It is important to ensure that larger fish cannot enter the floating cage over the top, so make sure that the sides extend at least 15 cm above the water level. 

 

Each of the vulnerable size classes should be kept in separate floating frames in the main fish tank. As the fish grow large enough not to be in danger, they can be moved into the main tank. With this method, it is possible to have up to three different stocking weights in one tank, so it is important that the fish feed pellet size can be eaten by all sizes of fish.

 

Caged fish also have the advantage of being closely monitored to determine the FCR by measuring the weight increment and weight of the feed over a period. 

 

8.4.3 Fish – summary

 

  • Add fish only after the fishless cycling process is complete, if applicable.
  • Feed the fish as much as they eat in 30 minutes, two times per day. Always remove uneaten feed after 30 minutes. Record total feed added. Balance the feeding rate with the number of plants using the feed rate ratio, but avoid over- or underfeeding the fish.
  • Fish appetite is directly related to water temperature, particularly for tropical fish such as tilapia, so remember to adjust feeding during colder winter months.
  • A fingerling tilapia (50 g) will reach harvest size (500 g) in 7–8 weeks under ideal conditions. Staggered stocking is a technique which involves stocking a system with new fingerlings each time some of the mature fish are harvested. It provides a way of maintaining relatively constant biomass, feeding rate, and nutrient concentration for the plants.

 

8.5 ROUTINE MANAGEMENT PRACTICES 

 

Below are daily, weekly and monthly activities to perform to ensure that the aquaponic unit is running well. These lists should be made into checklists and recorded. That way, multiple operators always know exactly what to do, and checklists prevent carelessness that can occur with routine activities. 

 

These lists are not meant to be exhaustive, but merely a guideline based on the systems described here in this publication and as a review of the management activities.

 

8.5.1 Daily activities 

  • Check that the water and air pumps are working well, and clean their inlets from obstructions.
  • Check that water is flowing.
  • Check the water level, and add additional water to compensate for evaporation, as necessary.
  • Check for leaks.
  • Check water temperature.
  • Feed the fish (1–2 times a day if possible), remove uneaten feed and adjust feeding rates.
  • At each feeding, check the behavior and appearance of the fish.
  • Check the plants for pests. Manage pests, as necessary.
  • Remove any dead fish. Remove any sick plants/branches.
  • Remove solids from the clarifier and rinse any filters.

 

8.5.2 Weekly activities

 

  • Perform water quality tests for pH, ammonia, nitrite, and nitrate before feeding the fish.
  • Adjust the pH, as necessary.
  • Check the plants looking for deficiencies. Add organic fertilizer, as necessary.
  • Clear fish waste from the bottom of fish tanks and in the biofilter.
  • Plant and harvest the vegetables, as required.
  • Harvest fish, if required.
  • Check that plant roots are not obstructing any pipes or water flow.

8.5.3 Monthly activities

 

  • Stock new fish in the tanks, if required.
  • Clean out the biofilter, clarifier, and all the filters.
  • Clean the bottom of the fish tank using fish nets.
  • Weigh a sample of fish and check thoroughly for any disease.

8.6 SAFETY AT WORK 

Safety is important for both the human operator and the system itself. The most dangerous aspect of aquaponics is the proximity of electricity and water, so proper precautions should be taken. 

Food safety is important to ensure that no pathogens are transferred to human food. Finally, it is important to take precautions against introducing pathogens to the system from humans. 

8.6.1 Electrical safety 

Always use a residual-current device (RCD). This is a type of circuit breaker that will cut the power to the system if electricity grounds into the water.

The best option is to have an electrician install one at the main electric junction. Alternatively, RCD adaptors are available, and inexpensive, at any hardware or home improvement store. An example of an RCD can be found on most hairdryers. This simple precaution can save lives. 

Moreover, never hang wires over the fish tanks or filters. Protect cables, sockets and plugs from the elements, especially rain, splashing water and humidity. There are outdoor junction boxes available for these purposes. 

Check often for exposed wires, frayed cables or faulty equipment, and replace accordingly. Utilize “drip loops” where appropriate to prevent water from running down a wire into the junction. 

8.6.2 Food safety 

Good agricultural practices (GAPs), should be adopted to reduce as far as possible any food-borne illnesses, and several apply to aquaponics. 

The first and most important is simple: always be clean. Most diseases that affect humans would be introduced into the system by the workers themselves. Use proper hand-washing techniques and always sanitize harvesting equipment. When harvesting, do not let the water touch the produce; do not let wet hands or wet gloves touch the produce either. If present, most pathogens are in the water and not on the produce.

Always wash produce after harvesting, and again before consumption. 

Second, keep soil and faeces from entering the system. Do not place harvesting equipment on the ground. Prevent vermin, such as rats, from entering the system, and keep pets and livestock away from the area. 

Warm-blooded animals often carry diseases that can be transferred to humans. Prevent birds from contaminating the system however possible, including through the use of exclusion netting and deterrents. 

If using rainwater collection, ensure that birds are not roosting on the collection area, or consider treating the water before adding it to the system. 

Preferably do not handle the fish, plants or media with bare hands, instead use disposable gloves. 

8.6.3 General safety 

Often aquaponic units, and farms and gardens in general, have other general hazards that can be avoided with simple precautions. A

void leaving power cords, air lines or pipes in walkways, as they can pose a trip hazard. Water and media are heavy, so use proper lifting techniques. Wear protective gloves when working with the fish and avoid the spines. 

Treat any scrapes and punctures immediately with standard first-aid procedures – washing, disinfecting and bandaging the wound. 

Seek medical attention, if necessary. Do not let blood or body fluids enter the system, and do not work with open wounds. 

When constructing the system, be aware of saws, drills and other tools. Keep acids and bases in safe storage areas, and use proper safety gear when handling these chemicals. 

Always keep all dangerous chemicals and objects properly stored and away from children.

8.6.4 Safety – summary

  • Use RCD on electric components to avoid electrocution.
  • Shelter any electric connections from rain, splashes, and humidity using correct equipment.
  • Adopt GAPs to prevent contamination of produce. Always keep harvesting tools clean, wash hands often, and wear gloves. Do not let animal feces contaminate the system.
  • Do not contaminate the system by using bare hands in the water.
  • Avoid trip hazards by keeping a neat workstation.
  • Wear gloves when handling fish and avoid spines.
  • Wash and disinfect wounds immediately. Do not work with open wounds. Do not let blood enter the system.
  • Be careful with power tools and dangerous chemicals, and wear protective gear.

8.7 TROUBLESHOOTING 

Table  8.4 lists the most common problems when running an aquaponic unit. If anything appears out of the ordinary, immediately check that the water pump and air pumps are functioning.

 Low DO levels, including accidental leaks, are the number one killer in aquaponic units. As long as the water is flowing, the system is not in an emergency phase and the problem can be addressed systematically and calmly. 

The first step is always to conduct a full water quality analysis. Understanding the water quality provides feedback essential for determining how to solve any problem.

TABLE 8.4 SKIPPED ****

8.8 Backup & Protection

 

8.8.1 Backup and Protection in iAVs Systems

In an Integrated AquaVegeculture System (iAVs), it is essential to have a backup plan and protection measures in place to ensure the health and productivity of both the aquatic and plant components. The following recommendations can help maintain the system during power outages and protect it from environmental factors and predators:

  1. Power Outage Preparations: The practicality of backup equipment depends on the expected frequency and duration of power outages. For example, tilapia can survive without aeration for extended periods, even up to a week or more. However, it’s crucial not to feed them if there’s no capacity to filter the resulting waste. In the event of short-term power outages, ranging from a few hours to a few days, it’s recommended to suspend the usual feeding schedule until aeration and pumping are restored.
  1. Basic Precautions: It’s generally more prudent to take basic precautions than to accept preventable losses or risks. Even in areas with minimal rainfall, it’s beneficial to cover, shade, or protect a tank. This helps to:Minimize evaporation losses
  1. Predator Protection: In some regions, predators could include osprey, eagles, hawks, foxes, raccoons, otters, two species of bears, and three species of felines. To protect the system from these predators, consider installing physical barriers, such as netting or fencing, around the tanks and growing areas.

 

8.9 CHAPTER SUMMARY 

The ten most important aspects of aquaponic unit management are:

  • Observe and monitor the system every day.
  • Ensure adequate aeration and water circulation with water pumps and air pumps.
  • Maintain good water quality: pH 6–8; DO ≥ 5 mg/litre; TAN ≤ 1 mg/litre; NO2- < 1 mg/litre; NO3- 5–150 mg/litre; temperature 18–30 °C.
  • Choose fish and plants according to seasonal climate.
  • Do not overcrowd the fish tanks (≤ 20 kg/1,000 litres).
  • Avoid overfeeding, and remove any uneaten food after 30 minutes.
  • Remove solid wastes, and keep tanks clean and shaded.
  • Balance the number of plants, fish, and size of biofilter.
  • Stagger harvesting and restocking/replanting to maintain balance.
  • Do not let pathogens enter the system from people or animals, and do not contaminate produce with system water by letting system water wet the leaves.

9. Additional topics on aquaponics 

This final chapter discusses minor, yet important, topics regarding the management of small-scale aquaponic units. 

Aquaponics requires several essential inputs, including fish feed, electricity, seeds/seedlings, fish fingerlings, supplemental plant fertilizer and water to replenish the unit. All of these inputs are available for purchase, yet there are simple methods of producing many of them domestically using sustainable practices.

These methods may reduce the unit running costs per year and help keep production as environmentally responsible as possible. 

Do not allow all of the water to drain from the aquaponic system. Broken pipes, loose fittings or unsecured hoses can drain all of the water. This would kill the fish and make a destructive mess in the process. 

Several techniques for fail-safes and redundancies are discussed to secure the water level. 

Finally, there is a brief discussion as to how aquaponics fits among other types of agriculture and how it can be further integrated.

9.1 SUSTAINABLE, LOCAL ALTERNATIVES FOR AQUAPONIC INPUTS 

9.1.1 Organic plant fertilizers 

Chapter  6 discussed how even balanced aquaponic systems can experience nutrient deficiencies. 

Although fish food pellets are a whole feed for fish, they do not necessarily have the right quantities of nutrients for plants. 

Generally, fish feeds have low iron, calcium and potassium values. Plant deficiencies can also arise in suboptimal growing conditions, such as cold weather and winter months. Thus, supplementary plant fertilizers may be necessary, particularly when growing fruiting vegetables or those with high nutrient demands. 

Synthetic fertilizers are often too harsh for aquaponics and can upset the balanced ecosystem; instead, aquaponics can rely on compost tea for any nutrient supplementation.

General composting process 

Compost is a rich fertilizer that is made from broken down organic matter, including food waste. 

Compost is extremely useful in soil-based gardening for replenishing organic material, retaining moisture and providing nutrients. 

In addition, compost can be used to create a liquid fertilizer, called compost tea, which can be added to the aquaponic water to boost the supply of nutrients. Conveniently, high-quality compost can be made from household food waste. 

Basically, food waste is added to a container, hereafter called the compost unit. Within the compost unit, aerobic bacteria, fungi and other organisms break the organic matter down into simple nutrients for plants to consume. 

The final substance that is produced is called humus. It consists of about 65 percent organic matter, is free of pathogens and is full of nutrients. 

The whole process from food waste to humus can take up to six months depending on the temperature inside the compost unit and quality of aeration. A compost unit is generally a 200–300 litre, barrel-shaped container with a lid and many vents (Figure 9.1). 

They are usually dark coloured to retain heat, which accelerates the decomposition process. Many types of compost units are available, and they are very easy to build with recycled parts. 

Compost units that tumble are recommended because they require less space and remain well-aerated and homogenous. 

Be sure to have enough space to spin the barrel properly. All compost units require adequate airflow. 

When making compost, it is important to manage the materials that are going into it. It is best to keep a good ratio of wet and dry organic material layered in equal amounts to reach a moisture content of about 60–70  percent. 

As the initial 2–3  weeks are a thermal aerobic process with temperatures up to 60–70  °C, it is important to avoid excessive moisture that would reduce the heat. 

The thermal stage accelerates the composting process and helps to pasteurize the organic wastes from any possible pathogens. The layering is important in order to keep the compost from being too wet and to prevent anaerobic zones. 

The frequent aeration of the pile is an important task in order to keep bacteria in aerobic conditions and to process the wastes uniformly. The operation consists of simply turning the waste upside down or periodically rotating the drum/container. This helps to aerate the aerobic bacteria. 

Good green compost can be obtained from a blend of wet materials, such as vegetable food leftovers, ground coffee, fruits and vegetables, and dry materials such as bread, grass clippings, dry leaves, straw, ash, and wood chips. 

However, it is important to keep an optimal balance between carbon and nitrogen (C:N ratio at 20–30) as it results in a rapid transformation of the material. In general, it is wise not to use too much straw or wood chips (C:N > 100) but rather use “green” wastes such as grass clippings, preferably slightly dried to reduce their moisture content. It is not recommended to use too much wood ash to avoid excessive pH increases, and to use only ash from wood/vegetable origin, as other sources (i.e. paper) may contain toxic substances. 

Some material should never be composted, including dairy, meat, citrus fruit, plastic, glass, metal and nylon. Compost is very forgiving, but ideally the compost should have enough moisture and nitrogen to feed all of the beneficial organisms. 

Water can be added if the compost is too dry. The rise in the temperature of the compost indicates intense microbial activity, indicating that the compost process is occurring. In fact, compost becomes so hot it can be used to heat greenhouses. 

Vermicomposting is a special method of composting that uses earthworms in the compost unit (Figure  9.2). 

There are several benefits to adding worms. 

First, they accelerate the process of decomposition as they consume organic wastes. Second, their waste (worm castings) is an extremely effective and complete fertilizer. Special vermicompost units can be bought or built, and there is a wealth of information available. It is important to source worms from a reputable source, and to ensure that they have never eaten meat or wastes from animals. 

Once composted, the worm castings can be used directly in the plant nursery to start seeds as this will introduce the nutrients to the aquaponic system once the seedlings are transplanted. Alternately, the worm castings can be made into a compost tea. 

Compost tea and secondary mineralization 

When the organic waste has finally decomposed into humus, which can take 4–6  months, it is possible to make compost tea. 

The process is simple. Several large handfuls of compost are tied within a mesh bag, weighted with some stones. This bag is suspended in a bucket of water (20  litres). An air stone connected to a small air pump is positioned underneath the mesh bag so that the bubbles agitate the contents (Figure  9.3). 

The aeration is very important to prevent anaerobic fermentation from occurring. 

The mixture is left for several days with constant aeration. The contents should be stirred occasionally to prevent any anoxic areas. After 2–3 days, the compost tea is ready to be used in the unit. 

The tea should be strained through a fine cloth and then diluted 1:10 with water. Apply to the plants either as a foliar feed in a spraying canister or as liquid fertilizer straight to the plant roots. If adding the diluted tea straight into the unit, begin by using small amounts (50 ml) and patiently document the change in the plant growth.

Re-apply when necessary, but be careful not to add too much. 

Other nutrient teas 

In addition to compost, there are many other nutrient-rich organic materials that can be brewed into nutrient tea in the way explained above. 

One mentioned above is to use the solid wastes from the fish tank, captured from the mechanical filter. Brewed in the same way, the solid wastes are completely mineralized and available to add back to the aquaponic system. 

Other sources include seaweeds, nettles and comfrey. Seaweed is a great addition because it is rich in potassium and iron, which are often lacking in aquaponics, but be sure to rinse residual salt from the seaweed. 

Larger amounts of organic fertilizer teas can also be used to temporarily maintain the aquaponic system without fish. 

This may be useful in the colder months of the year when fish metabolism is low and the plants need a boost of nutrients.

Compost safety 

When using compost make sure it is fully decomposed – making it pathogen-free. Never use organic sources from warm-blooded animals, which increases the risk of introducing pathogens. 

Moreover, make sure the water is well oxygenated and constantly aerated when producing the tea as this helps in mineralization and prevents some types of pathogenic bacteria from growing. 

Always avoid placing aquaponic water on the plants leaves, especially when using compost tea. 

For further information on brewing compost tea, see the section on Further Reading.

9.1.2 Alternative fish feed 

Fish feed is one of the most important and expensive inputs for any aquaponic system. It can be purchased or self-made. 

The authors strongly recommend the use of quality manufactured fish feed pellets because they are a whole food for fish, meaning the pellets fulfill all the nutritional needs of the fish. 

Even so, below is an example of supplemental fish feed that can be easily produced domestically, which can help save money or used temporarily if manufactured feeds are not available or too expensive. 

Further information on creating homemade feed pellets is available in Appendix 5.

Duckweed 

Duckweed is a fast-growing floating water plant that is rich in protein and can serve as a food source for carp and tilapia (Figure  9.4). 

Duckweed can double its mass every 1–2  days in optimum conditions, which means that onehalf of the duckweed can be harvested every day. 

Duckweed should be grown in a separate tank from the fish because otherwise the fish would consume the whole stock. 

Aeration is not necessary and water should flow at a slow rate through the container. Duckweed can be grown in sun-exposed or half-shaded places. Surplus duckweed can be stored and frozen in bags for later use. 

Duckweed is also a useful feed for poultry. Duckweed is a useful addition to an aquaponic system, especially if the duckweedgrowing container is located along the return line between the plants grow beds and the fish tank. 

Any nutrients that escape the plant grow beds fertilize the duckweed, thereby ensuring the cleanest water possible returning to the fish. 

Duckweed does not fix atmospheric nitrogen, and all of the protein in the duckweed ultimately comes from the fish feed or other outside sources.

Azolla, a water fern 

Azolla is a genus of fern that grows floating on the surface of the water, much in the manner of duckweed (Figure 9.5). 

The major difference is that Azolla is able to fix atmospheric nitrogen, essentially creating protein from the air. 

This occurs because Azolla has a symbiotic relationship with a species of bacteria, Anabaena azollae, which is contained within the leaves. As well as providing a free source of protein, Azolla is an attractive feed source because of its exceptionally high growth rate. 

Like duckweed, Azolla should be grown in a separate tank with slow water flow. Its growth is often limited by phosphorus, so if Azolla is to be grown intensively an additional source of phosphorous is needed such as compost tea.

Insects 

Insects are considered undesirable pests in many cultures. However, they have an enormous potential in supporting traditional food chains with more sustainable solutions. 

In many countries insects are already part of people’s diets and sold at the markets. In addition they have been used as animal feed for centuries. 

Insects are a healthy nutrient source because they are rich in protein and polyunsaturated fatty acids and full of essential minerals. 

Their crude protein content ranges between 13 and 77 percent (on average 40 percent) and varies according to the species, the growth stage and the rearing diet. Insects are also rich in essential amino acids, which are a limiting factor in many feed ingredients (Appendix 5). 

Edible insects are also a good source of lipids, as their quantity of fat can range between 9  and  67 percent. In many species, the content of essential polyunsaturated fatty acids is also high. These characteristics together make insects a healthy and ideal option for both human food and feed for animals or fish. 

Given their enormous number and varieties, the choice of the insect to be reared can be tailored to their local availability, climatic conditions/seasonality and type of feed available. The source of food for insects can include staple husks, vegetable leaves, vegetable wastes, manure and even wood or cellulose-rich organic materials, which are suitable for termites. Insects also make a great contribution to waste biodegradation, as they break down organic matter until it is consumed by fungi and bacteria and mineralized into plant nutrients. 

The culturing of insects is not as challenging as other animals since the only limiting factor is feed and not rearing space. Sometimes insects are referred to as “micro-livestock”. The small space requirement means that insect farms can be created with very limited areas and investment costs.

In addition, insect are cold-blooded creatures, this means that their feed conversion efficiency into meat is much higher than terrestrial animals and similar to fish. 

There are plenty of options possible and additional knowledge on insect farming as feed in the section on Further Reading. 

Among the many species available, an interesting species to be used as fish feed is the black soldier fly (see below).

Black soldier flies 

The larvae of black soldier flies, Hermetia illucens, are extremely high in protein and a valuable protein source for livestock, including fish (Figure 9.6). 

The lifecycle of this insect makes it a convenient and attractive addition to an integrated homestead farming system in favourable climate conditions. 

The larvae feed on manure, dead animals and food waste. When culturing black soldier flies, these types of waste are placed in a compost unit that has adequate drainage and airflow. 

As the larvae reach maturity, they crawl away from their feed source through a ramp installed in the compost unit that leads to a collection bucket. 

Essentially, the larvae devour wastes, accumulate protein and then harvest themselves. Two-thirds of the larvae can be processed into feed while the remaining one-third should be allowed to develop into adult flies in a separate area. 

The adult flies are not a vector of disease; adult flies do not have mouthparts, do not eat and are not attracted to any human activities. 

Adult flies simply mate and then return to the compost unit to lay eggs, dying after a week. Black soldier flies have been shown to prevent houseflies and blowflies in livestock facilities and can actually decrease the pathogen load in the compost. Even so, before feeding the larvae to the fish, the larvae should be processed for safety. 

Baking in an oven (170 °C for 1 hour) destroys any pathogens, and the resulting dried larvae can be ground and processed into a feed. 

Moringa or kalamungay 

Moringa oleifera is a species of tropical tree that is very high in nutrients, including proteins and vitamins. 

Classified by some as a super food and currently being used to combat malnutrition, it is a valuable addition to homemade fish feeds because of these essential nutrients. 

All parts of the tree are choice edibles suitable for human consumption, but for aquaculture it is typically the leaves that are used. 

In fact, there has been success in several small-scale aquaponic projects in Africa using leaves of this tree as the only source of feed for tilapia. 

These trees are fast-growing and droughtresistant and easily propagated through cuttings or seeds. However, they are intolerant of frost or freezing and not appropriate for cold areas. 

For leaf production, all of the branches are harvested down to the main trunk four times per year in a process called pollarding.

9.1.3 Seed collection 

Collecting seeds from growing plants is another important cost-saving and sustainable strategy in many types of small-scale agriculture. It is especially effective for aquaponics because the plants are the primary production goal. 

Seed collection is a straightforward process, which is discussed here as two major categories, dry seed pods and wet seed pods. 

In general, only use seeds from mature plants. Young plant seeds will not germinate, and old plants will have already dispersed their seeds. Avoid hybrid plants, which may be sterile. 

Collecting from many plants helps retain genetic diversity and healthy plants. In addition, consider local seed exchange groups that are available to trade seeds with other small-scale farmers. 

Dry seed pods 

This subcategory includes basil, lettuce, salad rocket and broccoli. Seeds from some of these plants can be harvested throughout the growing cycle, e.g. basil (Figure 9.7).

 Other seeds can only be collected after the plant is fully mature and no longer usable as a vegetable, e.g. lettuce and broccoli. 

The general process is to place the cut dry/mature stems into a large paper bag and store for 3–5 days in a cool, dark place. During this time, it is helpful to lightly shake the sealed paper bag to release the seeds.

Next, open the bag and shake the stem or whole plant one final time while still inside the bag. Then, remove the stems and all plant debris and pass them through a sieve to collect the remaining seeds. 

Gather these seeds and place them back into the paper bag, making sure that only seeds and no plant debris remain. 

Wet seed pods 

This sub-category includes cucumbers, tomatoes and peppers. 

The seeds develop inside the actual fruit, usually coated in a gel sac, which prohibits seed germination. When the fruits are ready to harvest, usually indicated by a strong and vibrant colour, remove the fruit from the plant, slice open the fruit with a knife and collect the seeds inside using a spoon. 

Take the seeds coated with gel and place into a sieve and begin washing off the gel with water and a smooth cloth. Then, take the seeds and lay them out and dry them out in the shade, flipping them occasionally until they are totally dry.

Finally, remove any remaining gel or plant debris and store them in a small paper bag.

Seed storage 

It is recommended to store seeds inside sealed paper bags or envelopes in a cool, dry and dark place with a minimum of moisture. A small refrigerator is a perfect place to store seeds, best if in an air-tight container with a desiccant bag (i.e. silica gel) to keep moisture below the required levels for fungi to grow. It is vital to make sure that only seeds are present with no other plant or soil debris to remove the risk of disease or premature germination. 

Plant debris and moisture can also encourage fungus and mould that can damage the seeds. Once placed into the bags, write on bag the date and type of plant. For high percentages of seed germination, the seeds should be used within 2–3 growing seasons. 

9.1.4 Rainwater harvesting 

Collecting rainwater to resupply aquaponic units is another effective way of reducing running costs. 

There are several benefits to using rainwater for aquaponics. First and foremost, rain is free. 

The aquaponic systems described in this publication lose 1–3 percent of their water per day, mostly from transpiration through the plant leaves. Water is a precious resource and can be expensive and unreliable in some areas. 

Second, most rainwater is high quality. Rainwater is unlikely to have toxins or pathogens. Rainwater does not contain any salts. Rainwater also has low levels of GH and KH, and is typically slightly acidic. This is quite useful, especially in areas where water has a strong alkalinity, because rainwater may offset the need for acid correction of incoming water to keep the aquaponic system within the optimal 6.0–7.0 pH range. However, the lower KH of rainwater means that rainwater is a poor buffer against acid changes in pH. 

Therefore, if using rainwater as the main source of water, calcium carbonate should be added, as described in Section 3.5.2. Be conscientious about the water collection surface, and try to avoid collecting water from around bird roosts or wherever animal faeces accumulate. 

A simple method to reduce any risk of pathogen contamination is through slow sand filtration, which can be obtained by simply percolating water into a fine sand filter 50–60 cm high and collecting the filtered water at the bottom opening of the tank. Rainwater collection can be easily achieved by connecting a large clean container to water drainage pipes surrounding a building or house (Figure 9.8). 

For example, a catchment area of 36 m2 will collect 11 900 litres of water with as little as 330 mm of rainfall per year. Some of this water is lost, but enough is caught to be sufficient for a smallscale aquaponic unit. The units described here use, on average, 2 000–4 000 litres of water per year. 

Collecting rainwater is the easy part; storing rainwater is more important and can be more challenging. The water has to be retained until the system needs it, and the water has to be kept clean. The containers should be covered with a screen to prevent mosquitoes and plant debris from entering. 

It also helps to keep a few small guppies or tilapia fry in the rainwater to eat insects, and a single air stone prevents anoxic bacteria from developing. 

9.1.5 Alternative building techniques for aquaponic units 

Human ingenuity has provided countless variations on the basic theme of aquaponics. At its most basic sense, aquaponics is simply putting fish and vegetables in different containers with shared oxygenated water. 

Old water tanks, bathtubs, plastic barrels, tables, wood and metal parts can all be used when building an aquaponic unit. Rafts and planting cups for DWC systems can be constructed from bamboo or recycled plastic; and media systems could be filled with locally available gravel. 

Always be sure that none of the components (fish tank, media beds, grow pipes and plumbing fittings) have been used previously to contain toxic or harmful substances that can hurt the fish, plants or humans. In addition, it is necessary to wash any material thoroughly before using it. 

The least expensive aquaponic system consists of one large hole in the ground, lined with cheap 0.6 mm polyethylene plastic pond liner. This pond is separated with wire or mesh to separate the fish from the plants. 

One side of the pond is the fish tank, stocked with a relatively low density of fish, while the other is a DWC canal covered with polystyrene foam. Aeration and water movement are always required, but can be added either through an airlift with low head height or through human powered pumping. Lifting water up to a header tank and allowing it to cascade back down is one method of adding oxygen without electricity. 

This approach can be used in places where barrels and IBC containers are too expensive for farmers to consider using, although overall production would be lower. Appendix  8 shows methods to make aquaponic units using IBCs, which can be easily found all around the world. In addition, the section on Further Reading lists two different guides on do-it-yourself aquaponics. 

9.1.6 Alternative energy for aquaponic units 

Operation of the unit’s electric pumps, both air and water, requires an energy source. Usually, the normal power mains are used, but it is not mandatory. 

These systems can be operated completely using renewable energy. It is outside the scope of this publication to specify the plans for building renewable energy systems, but useful resources are listed in the section on Further Reading.

Photovoltaic electricity 

Solar energy is an alternative and renewable energy that comes from sunlight. Photovoltaic panels convert the electromagnetic radiation from the sun to thermal energy or electricity (Figure 9.10). 

Water and air pumps for an aquaponic system can be powered with solar energy using photovoltaic solar cells, an AC/DC voltage inverter and large batteries to ensure 24  hour power supply at night or on cloudy days. 

Although highly sustainable, solar energy entails a large initial investment because of the costs of the extra equipment needed to convert and store the energy from photovoltaic cells. 

However, in some areas there are incentives to use solar energy which may help off-set these costs.

Insulation 

In winter, it may be necessary to heat the water. There are many methods to achieve this heating by using fossil fuels. 

However, cheaper and more sustainable options are available such as tank insulation and spiral heating. Insulating the fish tanks with standard insulation during the winter months prevents heat dispersing from fish tank. 

Significant heat energy is actually dispersed from the activity of the air stones, thus it is best to cover and insulate the biofilter or adopt alternative aeration solutions that avoid air bubbling.

Spiral heating 

Spiral heating is a form of passive heat capture from solar energy. Water from the system is circulated through black hose pipe, coiled in a spiral. The black plastic captures the heat from the sun and transfers it to the water. 

To further heat the system, the spiral heating coil can be contained within a small glass panel house that serves as a mini-greenhouse to further increase the heat. A black background can also help retain heat. 

For the systems described here, the recommended dimensions are a pipe 25  mm in diameter with a length of 40–80 m (Figure 9.11).

9.2 SECURING WATER LEVELS FOR A SMALL-SCALE UNIT 

One of the most common disasters for small-scale or commercial aquaponic units is a loss-of-water event where all of the water drains from the unit. This can be catastrophic and kill all of the fish, destroying the system. 

There are several common ways for this to happen, including electricity cuts, blocked pipes, drains left open, forgetting to add new water or disruption of water flow by animals. 

All of these issues can be fatal for fish in a matter of hours if problems are not dealt with immediately. 

Below is a list of methods to prevent some of the above situations.

9.2.1 Float switches 

Float switches are inexpensive devices used to control the pump depending on the water level (Figure 9.12). 

If the water level in the sump tank falls below a certain height, the switch will turn off the pump. This prevents the pump from pumping all of the water out of the tank. Similarly, float switches can be used to fill the aquaponic system with water from a hose or water main. 

A float switch similar to a toilet ballcock and valve can ensure that the water level never falls below a certain point. It should be noted that in certain types of loss-of-water events, such as a broken pipe, this method could ensure that the fish survive but actually make the flooding much worse, and it may not be appropriate for indoor applications. 

9.2.2 Overflow pipes 

REMOVE AND REPLACE WITH ALTERNATIVE!

Overflow pipes return water from the highest point in the unit back down to the sump in the event that the normal drainpipes become clogged (Figure 9.13). In these designs, the highest point is the fish tank, but other designs have the grow beds above the fish tank. Regardless, if pipes become blocked, which can occur if plant leaves, media or fish waste accumulate, the overflow pipes can safely drain water back down into the sump. This removes the risk of pumping the water out of the top of the system and draining the tanks. 

 

9.2.3 Standpipes 

REMOVE AND EXPLAIN WHY THIS IS NOT A GOOD IDEA – OR NEEDED!

Standpipes are used in bottom-draining tanks to prevent all of the water from draining out, typically installed in fish tanks. Within the tank in question, a vertical pipe is inserted into the drain (Figure  9.14). This technique defines the height of the water column; water neither gets deeper or shallower than the top of the pipe. However, this solution also means that the water from the bottom of the fish tank is not drained, unless a wider and taller pipe with wide openings at the bottom is positioned to concentrically surround the standpipe. By doing so, the water enters from the bottom and flows upward into the narrow interspace until it pours out from the standpipe’s top. This method is very secure, but requires that the outer pipe is occasionally moved to mobilize the wastes clogged in the interspace between the two pipes.  

 

9.2.4 Animal fences 

 

Opportunistic animals and birds can also cause loss of water by removing, displacing or breaking water pipes in the process of searching for water to drink or fish and vegetables to eat. 

 

To prevent this, a simple animal fence can be installed.

 

9.3 INTEGRATING AQUAPONICS WITH OTHER GARDENS 

Aquaponics can be used alone, but it becomes a stronger tool for the small-scale farmer when used in conjunction with other agriculture techniques

 

It has already been discussed how other plants and insects can be grown to supplement the fishes’ diet, but aquaponics can also help the rest of the garden. 

 

Generally, the nutrient-rich water from the aquaponic units can be shared among other plant production areas. 

 

9.3.1 Irrigation and fertilization 

Aquaponic units are a source of nutrient-rich water for vegetable production. This water can also be used to fertilize ornamental plants, lawns or trees. 

 

Aquaponic water is an excellent organic fertilizer for all soil-based production activities. For vegetables growing in raised beds or patches, aquaponic water can be periodically taken from the unit and irrigated onto the growing space, giving the soil a boost of essential nutrients for the vegetables. If growing larger fruiting vegetables (i.e. tomatoes) using satellite pots in the garden or in any space with good access to sunlight, aquaponic water can also be used as a nitrate-rich fertilizer during the early stages of leaf and stem development. Aquaponic water is also good for seed starting. 

 

9.3.2 Irrigating wicking beds 

 

Wicking beds are another form of raised bed garden that are extremely water-efficient. The bed itself has a water reservoir at the bottom of the container filled with large gravel. 

 

Above this gravel is a good mixture of moisture-retaining soil. These two zones are usually separated with shade cloth, geotextile or other fabric. The plants are planted within the soil. A refill pipe leads down through the top zone of soil down into the bottom zone of the water reservoir. 

 

The water is drawn upward from the reservoir into the root zone by capillary action (Figure 9.15). 

 

This removes the need for overhead watering and much less water is lost through evaporation. Roots growing in the moist soil have a continuous supply of water, oxygen and nutrients. 

 

Wicking beds can be watered with standard water, but using aquaponic water also supplies nutrients and avoids the need for fertilizers. A valve installed at the bottom of wicking bed containers helps to periodically flush the water preventing the buildup of salts and/or anaerobic zones. 

 

Wicking beds are an excellent method of growing vegetables in arid, water-scarce regions as only up to half of the water is needed compared with standard top-down irrigation methods. 

Wicking beds can be made out of water proof containers or dug into the ground and sealed with a polyethylene liner that stores the water, making them ideal methods to produce food in arid and semiarid urban areas with little or no access to soil (Figure 9.16). 

 

Another method is to place a wicking bed on top of a media bed within the aquaponic system proper. 

The fabric essentially creates a one-way passage, keeping soil out of the system but allowing water to percolate up into the root zone. 

This method can be used to grow tubers and root vegetables such as taro root, onions, beets and carrots. 

 

For further information on the wicking bed concept, see the sources listed in the section on Further Reading.

 

9.4 EXAMPLES OF SMALL-SCALE AQUAPONIC SETUPS 

 

Aquaponics has been used successfully in a wide range of locations. Moreover, aquaponic techniques have been revised to meet diverse needs and goals of farmers beyond the common IBC or barrel methods (described throughout this publication). 

 

There are many examples, but these were chosen to highlight the adaptability and diversity of the aquaponic discipline. 

 

9.4.1 Aquaponics for livelihood in Myanmar 

 

A pilot-scale aquaponic system was built in Myanmar to promote micro-scale farming during the implementation of an e-Women project funded by the Italian Development Cooperation. The goal was to create a productive unit under low-tech and low-cost criteria by using locally available materials and stand-alone solar energy. 

 

The system hosted tilapia and a wide range of vegetables (Figure 9.17). 

 

The system was used for the development of a cost–benefit analysis, inclusive of depreciation, for householdscale systems with the objective to meet the daily income target of USD1.25 set by the Millennium Development Goal. Using local prices, a 27 m2 aquaponic system placed within a bamboo net house and powered by solar panel costs USD25/m2 . 

 

This system provides a net profit of USD1.6– 2.2/day from vegetables, and a daily ration of 400 g of tilapia for home consumption. The payback period is 8.5–12 months depending on the crops. The net house prevents any need for pest control and avoids seasonality by securing income against adverse climatic conditions (rain). 

 

Fry nursing, very common among farmers in Southeast Asia, could be another interesting option in aquaponics to further boost incomes in poor or landless households. This pilot project showed that aquaponics could play an important role in securing food and livelihood in many areas across the world. 

The production of fish and plants with small plots allows vulnerable people to produce income, adds value to household work and empowers women at community level.

 

9.4.2 Saline aquaponics 

 

The integration of marine or brackish water aquaculture with agriculture provides new ways to produce food in coastal or saline-prone areas where traditional farming cannot be developed. 

 

The inland culturing of aquatic animals, beyond the environmental benefits derived from pollution or landscape restoration, is beneficial for the greater control of the production factors and the reduction of the risks related to contaminants or pathogens. 

 

Even though saltwater is not ideal for plants, as it creates osmotic shocks, limits growth and procures sodium toxicity, it is still possible to grow some useful plants in lower salinity. A wide range of plants can benefit from the nutrient-rich water obtainable from aquaponics or closed recirculating systems. 

 

Halophytes (salt-tolerant species) can boost food output in arid and saline areas and raise farm productivity. Some species are highly-valued speciality crops, such as Salsola spp. (Figure  9.18), sea fennel, Atriplex spp. or Salicornia spp., while other are cropped for grains, such as pearl millet, quinoa and eelgrass, and still others can be grown for biodiesel. 

 

Ideal saline conditions for halophytes are in the salinity range of one-third to one-half of sea strength, but some plants are tolerant to hypersaline conditions. 

 

Adapting horticultural plants to saline water is one of the greatest challenges of modern agriculture. 

 

However, it is possible to grow some horticultural species directly with brackish-water. Most of the plants belonging to the Chenopodiaceae family (beet, chard) can easily grow in a salinity of one-sixth to one-third of sea strength owing to their higher resistance to salt. 

 

Other common species such as tomato and basil can achieve substantial production up to one-tenth of sea strength (Figure 9.20) providing that tailored agronomic strategies are adopted: increased concentrations of nutrients, plant bio-conditioning, grafting with salt-tolerant rootstocks, improved climate control and higher planting densities. 

 

Nevertheless, the qualitative traits of saline crops are higher than freshwater, both for their organoleptic characteristics, taste and shelf-life. 

 

9.4.3 Bumina and Yumina 

 

There is an aquaponic technique from Indonesia that deserves special attention. In Bahasa Indonesia, this technique is called bumina and yumina, translated literally as “fruit–fish” and “vegetable–fish”. 

 

This name demonstrates how intimately linked the plants and the fish are within an aquaponic system. Bumina and yumina are essentially a version of the media bed technique. 

 

The fish are housed within an in-ground pond dug into the earth and lined with sandbags or hollow-form bricks. This pond is lined with a tarp, or better, a polyethylene liner. The liner is necessary to prevent unwanted biological and chemical reactions occurring within the sediments on the bottom and helps to keep the system clean. 

 

Alternately, the fish are housed within a raised concrete cistern. 

 

Water is pumped out of this pond into a header tank, usually constructed out of a large plastic barrel. This barrel can contain mechanical and biological filter material if the stocking density is high enough to require it. From this header barrel, the water is fed, by gravity, through a distribution pipe. The entire pond is lined with satellite pots, simple flower pots or other small containers that are full of organic growing media. The distribution pipe lays atop these satellite pots and water is delivered through small holes. 

 

The water irrigates and fertilizes the plants in these pots, and then exits the bottom of the pots back into the fish pond (Figure 9.21). The cascading water effect also helps to aerate the fish pond. Bumina and yumina are used as an important component of homestead food security initiatives throughout Indonesia aimed at increasing home protein production. 

 

The initial investment of these systems is smaller than that of the IBC systems outlined in this publication, but they require an in-ground pond so are inapplicable for some urban, indoor or rooftop applications.  

 

9.5 CHAPTER SUMMARY

 

  • Compost tea can be used to supplement nutrients for the plants and be produced on a small-scale by composting vegetable wastes.
  • Alternative and supplemental fish feed can be grown and produced on a small scale, including duckweed, Azolla spp., insects, and moringa.
  • Seeds can be collected and stored using simple techniques to reduce costs of reseeding.
  • Rainwater collection and storage provides a cost-effective way of replenishing aquaponic water.
  • Redundancies and failsafe methods should be employed to prevent catastrophic loss-of-water events that can kill the fish.
  • Aquaponic water can be used to fertilize and irrigate other gardening activities.
  • Many types and methods of aquaponics exist beyond the examples outlined in this publication.

10 – Business / Commercial Aspects

10.1 Investigating the Profitability of Integrated AquaVegeculture Systems

The profitability of Integrated AquaVegeculture Systems (iAVs)depends on various factors such as scale, climate, location, market prices, and skill level. A recent analysis suggests that the annual Internal Rate of Return (IRR) at operational capacity can range from 150% to 400%, depending on the accounting methodology applied to depreciation, opportunity costs, and taxation aspects.

 

A state-of-the-art 5-acre composite facility in the US, with 3.7 acres of production dedicated to organic tomato and tilapia, is projected to generate between $6 to $7 million in gross product value per year. Net pre-tax returns are estimated to range from $250 to $300 per square meter per year (with facility depreciation and interest expensed) or from $350 to $400 per square meter per year (without depreciation and interest costs factored). 

The total developed cost, including land, regulatory compliance factors, professional fees, rain catchment/storage/treatment, post-harvest handling, IPM integration, internal hatchery, fish processing, etc., is estimated at $10 million, with a possible variation of +/- 20% without considering the optional natural gas tri-generation plant (electric, heat, and CO2).

 

Dr. Mark McMurtry, the inventor of iAVs, has compared the floating raft aquaponics method with iAVs, highlighting the distinct differences between the two systems. iAVs predates the development of modern aquaponics systems and is considered a separate approach to integrating fish and plant cultivation.

 

The profitability of iAVs is influenced by numerous variables, and its success depends on the careful consideration of factors such as initial investment, annual operating costs, and realistic market price estimates. As interest in iAVs and similar systems grows, further research and analysis will be crucial in determining the most effective strategies for maximizing returns and ensuring the long-term viability of these innovative agricultural methods.

 

10.2 Commercialization of iAVs

 

Production and Marketing: Two Sides of the Same Coin

In the realm of Integrated AquaVegeculture Systems (iAVs), achieving commercial volumes of production is often considered the straightforward part, assuming the presence of competent skills, sufficient capital, commitment, experience, and contingency planning. However, the marketing of perishable commodities at volume, ensuring they are sold in a timely manner with a profit margin, is a complex task not suited for novices. Both fish and produce have distinct, established channels for distribution.

 

Commercial success in iAVs requires more than just high-volume production. It necessitates a combination of skills, experience, and resources. Growing and selling are two vastly different enterprises, each requiring its own set of skills. To be profitable, both must be executed effectively and efficiently.

The Art of Pre-Selling

Large scale growers often grow their products under contract, which means the product is pre-sold at an assured volume, quality, timeframe, and price. This practice is common among commercial growers, whether they are producing bedding plants, cut flowers, high-performance tomatoes, peppers, or virtually any other crop. Most field vegetable crops in the US are also grown under contract, essentially pre-sold.

 

In a greenhouse context, scheduling to target favorable market conditions is often critical to success. Staggered production, such as constant daily or weekly harvest volumes, requires dynamic stocking/planting management scheduling versus static batch production. This approach is only practical at a significant scale.

The Importance of Understanding the Market

Many enthusiasts may not fully understand how food commodities are distributed and marketed, and the skill sets involved. The choice of crop or production methodology has little to no bearing on the ability to sell volume at a profit reliably. Growing and marketing are vastly different endeavors, and neither should be attempted by novices in a commercial context.

 

10.3 Commercialization Challenges in iAVs

 

Understanding the Novice’s Journey

It’s not uncommon for individuals new to the field, or “novices,” to venture into commercial operations, including those related to Integrated AquaVegeculture Systems (iAVs). This decision, while seemingly straightforward, may not be as clear to some as it is to others. Enthusiasm, while a valuable asset, can sometimes mask a lack of experience or understanding, leading to potential pitfalls1.

The term “novice” here refers to individuals who lack professional experience across a range of disciplines. Even those with good intentions and a knack for growing can find themselves in financial trouble if they dive into commercial operations without adequate preparation or understanding of the industry1.

The Risk of Over-Optimism

Over-optimism, often unfounded, can lead to failure in commercial ventures. This is true regardless of the effort or activity involved. It’s important to understand that no single individual possesses all the skills necessary to commercialize a system like iAVs or any other venture. Recognizing one’s strengths and weaknesses is a crucial step in the journey towards successful commercialization.

The Importance of Collaboration

Successful commercialization often requires collaboration. Major success stories in the field often involve a combination of different skills and expertise. However, it’s equally important to acknowledge that failure is often easier to achieve, and it’s usually due to a lack of understanding or over-optimism.

The Role of Experience

Experience plays a significant role in the success of commercial ventures. Many well-intentioned growers, even those with a gift for it, have faced bankruptcy due to a lack of experience and understanding of the industry. It’s crucial to approach commercialization with a realistic understanding of the challenges and potential risks involved.

 

11 – Case Studies

11.1 Gordon Watkins

In 2017, a member of a Facebook group discovered an article about an Integrated AquaVegeculture System (iAVs) established in 1998. The system is still operational 26 years later. The owner, Gordon Watkins, an organic farmer and tropical fish hobbyist from Arkansas, shared the story of his iAVs journey.

The Beginning

Watkins first learned about Dr. Mark McMurtry’s iAVs research project at North Carolina State University in 1990. After attending a workshop on “Integrated Greenhousing,” he decided to explore iAVs as a way to diversify his organic blueberry production and enable year-round farming. He built a small experimental iAVs to test the design and assess local markets for tilapia and pacu.

The Greenhouse

The 22′ x 14′ greenhouse, completed in October 1997, was attached to the southern side of Watkins’ house. It featured a cement block foundation, white oak and redwood framing, twin-wall polycarbonate roofing, and recycled insulated glass panels. The south wall had top-hinged Thermopane windows with Bayless solar vent openers for ventilation, and a 20-inch thermostatically-operated exhaust fan provided additional airflow. Large sliding windows connected the greenhouse to the house, serving as part of the passive climate control system.

The iAVs

The iAVs system consisted of a poured concrete vat (22′ x 4′ and 2.5′ deep) with a V-shaped bottom, set in the ground. The tank was divided into five sections with removable partitions, allowing fish to be segregated by species, size, and sex. The tank was covered by 4′ x 2′ slatted panels made from black locust wood, which also served as a walkway. The panels provided 50% shade to the tank and were easily removed when working with the fish.

 

Adjacent to the walkway was a 22′ x 8′ (12″ deep) sand biofilter filled with sand and gravel. The sand bed walls were made from cement blocks, and the outflow from the bed flowed underneath the wall before draining back into the fish tank. Watkins applied aquaculture-suitable epoxy to all concrete surfaces to prevent lime leaching, which could cause pH control issues.

The Plants and Fish

Watkins planted water-loving plants like watercress, chives, and emergent aquarium plants. He introduced 12 lbs (250 individuals) of hybrid all-male tilapia into the system in October 1997. By January 1997, he estimated the fish load to be 60 lbs and planned to use fish spawned in his system to stock it until it reached the expected carrying capacity of 0.5 lbs/gallon or 750 lbs of fish.

Balancing the System

Achieving the proper balance between the biological load (quantity of fish produced) and the biofilter capacity is critical to the successful operation of the iAVs. Watkins believed that a 1:1 ratio was optimum for fish and plant production. He noted that different crops absorb different amounts of nutrients, which affects the nutrient cycle. However, he believed that if a flexible ratio was used, the system would be adaptable enough to allow some variation in stocking rates, planting densities, and crop choices.

26 Years Later

Fast-forward 26 years, and the iAVs is still operating, albeit in ‘maintenance mode’. It is currently planted with ferns and a few other perennials, and the greenhouse temperature is maintained solely by passive solar heat. There has been little noticeable reduction in percolation rates. Gordon Watkins’ 26-year-old iAVs debunks the myth about sand clogging and adds an important second voice about the development of the method.

 

11.1.2 Boone Mora

 

In the early 1990s, Boone Mora and his team at the North Central Regional Aquaculture Center (NCRDC) embarked on an ambitious project to explore the potential of the Integrated AquaVegeculture System (iAVs). Operating a 10,000 sq. ft facility in rural North Carolina, the team set out to test the profitability of this innovative approach to horticulture and aquaculture.

 

Key aspects of the project included:

  • Facility: The 10,000 sq. ft facility was not spatially optimized or environmentally regulated, indicating potential for further efficiency improvements.
  • Costs: All costs were accounted for in the project, including the repayment of a presumptive loan for the greenhouse’s construction and first-year operating expenses.
  • Labor: All labor costs were covered, including payment for the owner/operator’s time, although specific rates were not provided.
  • Production: All production, including tilapia, tomatoes, and peppers, was sold at a flat rate of $1/lb.

Despite the challenges, Mora’s team reported an annual profitability in the range of $30,000 to $40,000. This was a significant achievement, especially considering the rural location and the time period (1992-94). However, Mora himself considered this a small-scale commercial demonstration, not quite reaching full commercial scale by today’s greenhouse standards.

 

The case of Boone Mora highlights the significant potential of iAVs, especially when considering the economies of scale. With further optimization and scaling, the profitability of such a system could be significantly improved. 

 

Furthermore, it’s important to note that the value of a dollar has changed significantly since the early 1990s, further emphasizing the potential for improved profitability in today’s terms.

 

Further reading 

Recirculating aquaculture and fish breeding 

Lim, C. & Webster, C.D. 2006. Tilapia: biology, culture, and nutrition. Bing Hampton, USA, Haworth Press. 678 pp. 

Timmons, M.B. & Ebeling, J.M. 2010. Recirculating aquaculture. Ithaca, USA, Cayuga Aqua Ventures. 975 pp. 

Szyper, J.P., Tamaru, C.S., Howerton, R.D., Hopkins, K.D., Fast, A.W. & Weidenbach, R.P. 2001. Maturation, hatchery and nursery techniques for Chinese catfish, Clarias fuscus, in Hawaii. Aquaculture Extension Bulletin. University of Hawaii Sea Grant College Program. 

Woynarovich, A., Moth-Poulsen, T. & Péteri, A. 2010. Carp polyculture in Central and Eastern Europe, the Caucasus and Central Asia: A manual. FAO Fisheries and Aquaculture Technical Paper. No. 554. Rome, FAO. 73 pp. (also available at: www.fao.org/docrep/ 013/i1794e/i1794e00.htm).

Species profiles 

FAO. 2014. Species profiles. In: FAO Aquaculture Feed and Fertilizer Resources Information System [online]. Rome. [Cited 2 September 2014]. www.fao.org/fishery/affris/species-profiles/en/ 

FAO. 2014. Nile tilapia – Oreochromis niloticus. In: FAO Aquaculture Feed and Fertilizer Resources Information System [online]. Rome. [Cited 2 September 2014]. www.fao.org/fishery/affris/species-profiles/nile-tilapia/nile-tilapia-home/en/ 

FAO. 2014. Common carp – Cyprinus carpio. In: FAO Aquaculture Feed and Fertilizer Resources Information System [online]. Rome. [Cited 2 September 2014]. www.fao.org/fishery/affris/species-profiles/common-carp/common-carp-home/en/  

Aquaponics 

Backyard Aquaponics. 2011. The IBC of aquaponics [online]. Edition 1.0. Backyard Aquaponics, Success Western, Australia. Available at: www.backyardaquaponics.com/Travis/IBCofAquaponics1.pdf 

Bailey, D.S., Rakocy, J.E., Cole, W.M. & Shultz, K.A. 1997. Economic analysis of a commercial-scale aquaponic system for the production of tilapia and lettuce. In: Tilapia Aquaculture: Proceedings of the Fourth International Symposium on Tilapia in Aquaculture, Orlando, Florida. 

Bernstein, S. 2011. Aquaponic gardening: a step-by-step guide to raising vegetables and fish together. Gabriola Island, Canada, New Society Publishers. 255 pp. 

Danaher, J.J., Pantanella, E., Rakocy, J.E., Shultz, R.C. & Bailey, D.S. 2011. Dewatering and composting aquaculture waste as a growing medium in the nursery production of tomato plants. Acta Hort. (ISHS) 891. pp. 223–229. 

Diver, S. 2007. Aquaponics-integration of hydroponics with aquaculture. ATTRA – National Sustainable Agriculture Information Service. 46 pp. 

Gloger, K.C., Rakocy, J.E., Cotner, J.B., Bailey, D.S., Cole, W.M. & Shultz, K.A. 1995. Waste treatment capacity of raft hydroponics in a closed recirculating fish culture system. World Aquaculture Society, Book of Abstracts. pp. 126–127. 

Hughey, T.W. 2005. Barrel-ponics (a.k.a. aquaponics in a barrel) [online]. Available at: www.aces.edu/dept/fisheries/education/documents/barrel-ponics.pdf

Lennard, W.A. & Leonard, B.V. 2006. A comparison of three different hydroponic subsystems (gravel bed, floating and nutrient film technique) in an aquaponic test system. Aquaculture International, 14(6): 539–550. 

Pantanella, E. 2012. Integrated marine aquaculture-agriculture: sea farming out of the sea. Global Aquaculture Advocate, 15(1): 70–72. 

Pantanella, E., Cardarelli, M. & Colla, G. 2012. Yields and nutrient uptake from three aquaponic sub-systems (floating, NFT and substrate) under two different protein diets. In: Proceedings. AQUA2012. Global Aquaculture securing our future. Prague, Czech Republic 1-5 Sept 2012. Pantanella, E., Cardarelli, M., Colla, G., Rea, E. & Marcucci, A. 2011. Aquaponics vs hydroponics: production and quality of lettuce crop. Acta Hort. 927. pp. 887–893. 

Rakocy, J.E. 2007. Aquaponics, integrating fish and plant culture. In T.B. Simmons & J.M. Ebeling, eds. Recirculating aquaculture, pp. 767–826. Ithaca, USA, Cayuga Aqua Ventures. Rakocy, J.E. 2007. Ten guidelines for aquaponic systems. Aquaponics Journal, 46: 14–17. Rakocy, J. E., Masser, M.P. & Losordo, T.M. 2006. Recirculating aquaculture tank production systems: aquaponics-integrating fish and plant culture. SRAC publication 454. 1–16. 

Rakocy, J.E, Masser, M.P. & Losordo, T.M. 2006. Recirculating aquaculture tank production systems: aquaponics-integrating fish and plant culture. SRAC Publication No. 454 (revision November 2006). USA, Department of Agriculture. R

akocy, J.E., Shultz, R.C., Bailey, D.S. & Thoman, E.S. 2004. Aquaponic production of tilapia and basil: comparing a batch and staggered cropping system. Acta Horticulturae 648. pp. 63–69. 

Savidov, N. 2005. Evaluation and development of aquaponics production and product market capabilities in Alberta. Phase II. Final Report – Project #2004-67905621. 

Seawright, D.E., Stickney, R.R. & Walker, R.B. 1998. Nutrient dynamics in integrated aquaculture-hydroponic systems. Aquaculture, 160: 215–237. 

Tyson, R.V., Simonne, E.H., White, J.M. & Lamb, E.M. 2004. Reconciling water quality parameters impacting nitrification in aquaponics: the pH levels. Proc. Fla. State Hort. Soc., 117: 79–83.

Bacteria, microbes and the nitrogen cycle 

Carmignani, G.M. & Bennett., J.P. 1977. Rapid start-up of a biological filter in a closed aquaculture system. Aquaculture, 11(1): 85–88. 

Crab, R., Avnimelech, Y., Defoirdt, T., Bossier, P. & Verstraete, W. 2007. Nitrogen removal techniques in aquaculture for a sustainable production. Aquaculture, 270: 1–14. 

Hargreaves, J.A. 1998. Nitrogen biogeochemistry of aquaculture ponds. Aquaculture, 166: 181–212. 

Lewis, W. & Lowenfels, J. 2010. Teaming with microbes: a gardener’s guide to the soil food web. Portland, USA, Timber Press. 220 pp.

Bell siphon design and construction 

Fox, B.K., Howerton, R. & Tamaru, C.S. 2010. Construction of automatic bell siphons for backyard aquaponic systems. Cooperative Extension Service, College of Tropical Agriculture and Human Resources, University of Hawaii at Mānoa. Lennard, W.A. & 

Leonard, B.V. 2004. A comparison of reciprocating flow versus constant flow in an integrated, gravel bed, aquaponic test system. Aquaculture International, 12: 539–553.

Fish feeds 

Bondari, K. & Sheppard, D.C. 1981. Soldier fly larvae as feed in commercial fish production. Aquaculture, 24: 103–109.

FAO. 1983. FAO composition of feedstuff (Table 1). In: Fish feeds and feeding in developing countries. ADCP/REP/83/18. Rome. (also available at: www.fao.org/docrep/q3567e/ q3567e03.htm#2.2%20composition%20of%20feedstuffs). 

FAO. 2013. Edible insects: future prospects for food and feed security. FAO Forestry Paper 171. Rome. 187 pp. (also available at: www.fao.org/docrep/018/i3253e/i3253e00.htm). 

FAO. 2014. FAO feed resources database. In: FAO Aquaculture Feed and Fertilizer Resources Information System [online]. Rome. [Cited 2 September 2014]. www.fao.org/fishery/affris/feed-resources-database/en/ 

Fasakin, E.A., Balogun, A.M. & Fasuru, B.E. 1999. Use of duckweed, Spirodela polyrrhiza L. Schleiden, as a protein feedstuff in practical diets for tilapia, Oreochromis niloticus L. Aquaculture Research, 30(5): 313–318. 

Hasan, M.R. & Chakrabarti, R. 2009. Use of algae and aquatic macrophytes as feed in small-scale aquaculture: A review. FAO Fisheries and Aquaculture Technical Paper. No. 531. Rome, FAO. 123 pp. (also available at: www.fao.org/docrep/012/i1141e/i1141e00.htm). 

New, M.B. 1987. Feed and feeding of fish and shrimp. ADCP/REP/87/26. Rome, FAO. (also available at: www.fao.org/docrep/s4314e/s4314e00.htm#Contents). 

NRC. 1993. Nutrient requirement of fish. Washington, DC, National Academy Press. 126 pp. 

Richter, N., Siddhuraju, P. & Becker. K. 2003. Evaluation of nutritional quality of moringa (Moringa oleifera Lam.) leaves as an alternative protein source for Nile tilapia (Oreochromis niloticus L.). Aquaculture, 217(1): 599–611. 

Sheppard, D.C., Tomberlin, J.K., Joyce, J.A., Kiser. B.C. & Sumner, S.M. 2002. Rearing methods for the black soldier fly (Diptera: Stratiomyidae). J. Med. Entomol., 39(4): 695–698. 

Sophie St-Hilaire, I.S., Cranfill, K., McGuire, M.A., Mosley, E.E., Tomberlin, J.K., Newton, L., Sealey, W., Sheppard, C. & Irving, S. 2007. Fish offal recycling by the black soldier fly produces a foodstuff high in omega-3 fatty acids. Journal of the World Aquaculture Society, 38(2): 309–313. 

Wagner, G.M. 1997. Azolla: a review of its biology and utilization. Botanical Review, 63(1): 1–26.

Compost tea 

Brewing Compost Tea. Fine Gardening. Brewing Compost Tea by Elaine Ingham. Available at: www.finegardening.com/brewing-compost-tea. 

Ingham, E.R. 2000. The compost tea brewing manual. Fifth edition. Corvallis, USA, Soil Foodweb Incorporated. 79 pp.

Fish diseases 

Bondad-Reantaso, M.G., McGladdery, S.E., East, I. & Subasinghe, R.P., Eds. 2001. Asia Diagnostic Guide to Aquatic Animal Diseases. FAO Fisheries Technical Paper. No. 402, Supplement 2. Rome, FAO. 240 pp. (also available at: www.fao.org/docrep/005/y1679e/y1679e00.htm). 

Noga, E.J. 1996. Fish disease, diagnosis and treatment. St. Louis, USA, Mosby Year-Book inc. 367 pp.

Greenhouses and net houses 

FAO. 1999. Greenhouses and shelter structures for the tropics. Plant Production and Protection Paper 154. Rome. 138 pp. 

FAO. 2013. Good agriculture practices for greenhouse vegetable production: Principles for the Mediterranean climate areas. Plant Production and Protection Paper 217. Rome. 621 pp. (also available at: www.fao.org/docrep/018/i3284e/i3284e.pdf) 

Nutrient deficiencies 

Bennett, W.F. 1993. Nutrient deficiencies and toxicities in crop plants. St. Paul, USA, American Phytopathological Society. 202 pp. 

Berry, W. 2010. Symptoms of deficiency in essential minerals [online]. UCLA. Lincoln Plant Physiology online. Fifth edition. Available at: http://5e.plantphys.net/article.php?ch=t&id=289

Plant diseases 

Agrios, G.N. 2004. Plant pathology. Fifth edition. Burlington, USA, Elsevier Academic Press. 933 pp. 

Copping, L.G. 2004. The manual of biocontrol agents. Third edition. Alton, UK, BCPC publications. 702 pp. 

Cornell University. Plant Disease Diagnostic Clinic [online]. Available at: http://plantclinic.cornell.edu/factsheets.html 

IFOAM. 2012. The IFOAM norms for organic production and processing. Bonn, Germany. 132 pp. 

Pal, K.K. & McSpadden Gardener, B. 2006. Biological control of plant pathogens. The Plant Health Instructor DOI: 10.1094/PHI-A-2006-1117-02. pp. 1-25. 

Soil Association. 2011. Material for pest and disease control in organic crops. Fact sheet. Bristol, UK, Soil Association Trade and Producer Support. 18 pp. 

Texas A&M Agrilife Extension. Texas plant disease handbook [online]. Available at: http://plantdiseasehandbook.tamu.edu/food-crops/vegetable-crops/

Pest management 

ATTRA National Sustainable Agriculture Information Service. Pest management [online]. Available at: https://attra.ncat.org/pest.html 

Colorado State University Extension. Insect publication [online]. Available at: www.ext.colostate.edu/pubs/pubs.html#insects 

Cranshaw, W.S. 2008. Bacillus thuringiensis [online]. Factsheet 5.556. Colorado State University Extension. Available at: www.ext.colostate.edu/pubs/insect/05556.html 

Ellis, B.W. & Bradley, F.M. 1996. The organic gardener’s handbook of natural insect and disease control. Emmaus, USA, Rodale Press Inc. 544 pp. 

Kogan, M. 1998. Integrated pest management: historical perspectives and contemporary developments. Annual Review of Entomology, 43(1): 243–270. 

Olkowski, W., Dietrick, E., Olkowski, H. & Quarles, W. 2003. Commercially available biological control agents. IPM Practitioner, 25: 1–9. 

Rondon, S.I., Cantliffe, D.J. & Price, J. 2001. Augmentative biological control of insects: possibilities for vegetable greenhouse producers. FACTS Proceedings 2001, pp. 15–16. 

Shour, M.H. 2000. Pesticides from nature [online]. Iowa State University Extension. Available at: www.extension.iastate.edu/newsrel/2000/aug00/aug0007.html 

Washington State University (WSU). 2011. Organic pest control in the vegetable garden [online]. Community Horticulture Fact Sheet #13. King County Extension. Available at: http://ext100.wsu.edu/king/wp-content/uploads/sites/17/2014/02/ Organic-Pest-Control-in-the-Vegetable-Garden1.pdf 

UW Madison Department of Entomology. Insect ID [online]. Available at: www.entomology.wisc.edu/insectid/index.php 

Soil-less culture 

Cooper, A. 1979. The ABC of NFT. Nutrient film technique. The world’s first method of crop production without a solid rooting medium. Portland, USA, Intl Specialized Book Service Inc. 181 pp. 

Raviv, M. & Lieth, J.H. 2008. Soil-less culture: theory and practice. First edition. London, Elsevier Publishing. 608 pp

Resh, H.M. 2004. Hydroponic food production. A definitive guidebook for the advanced home gardener and the commercial hydroponic grower. Sixth edition. Mahwah, USA, Newconcept Press. 567 pp.

Wicking beds 

Sullivan, C., Hallaran, T., Sogorka, G. & Weinkle, K. 2014. An evaluation of conventional and subirrigated planters for urban agriculture: Supporting evidence. Renewable Agriculture and Food Systems, 1–9. 

Wicking bed. Wicking bed – a new technology for adapting to climate change [online]. pp. 1–14. Available at: www.waterright.com.au/wicking_bed_technology.pdf 

Wicking worm bed. Wicking worm bed. Basic principles [online]. pp. 1–10. Available at: www.waterright.com.au/Wicking%20worm%20beds.pdf 

Glossary

Acid – A substance characterized by the ability to react with bases or alkalis in water to form salts. An acid releases hydrogen ions upon dissociation in water, having a pH of less than seven.

AC/DC – A type of electrical device that can function both with alternating current (AC), such as that from a wall socket, and direct current (DC), such as that from a battery. Usually used in regard to battery-based backup systems for aerators and water pumps.

Aerobic – A condition or process where gaseous oxygen is present or required. Aerobic organisms obtain energy for growth from aerobic respiration.

Alkalinity – Amount of alkaline minerals (acid binding) that a solution has in the water to neutralize hydrogen ions. It is usually expressed as SBV units (abbreviation of the German term Säurebindungsvermögen) or equivalents of calcium carbonate under the conversion factor of 1 SBV = 50 mg eq. CaCO3/litre. Alkalinity is measured by using methyl orange as an indicator, whose variation in colour at pH 4.2–4.4 indicates, by definition, the complete depletion of alkali.

Anaerobic – Referring to a condition or process where gaseous oxygen is not present or not necessary.

Autosiphon – A device that automatically floods and drains a water tank without a timer or moving parts. Incoming water fills the tank in question until it reaches the critical height set by the siphon; this starts pulling water out of the tank with an outflow faster than the inflow, which eventually empties the tank and lets air enter the device to break the draining and allow the tank to refill.

Base – A substance characterized by the ability to react with acids or hydrogen ions in water to form salts. A base releases hydroxide ions upon dissociation in water and has a pH of higher than seven.

Balance – A state of dynamic equilibrium in an integrated agricultural system, such as aquaponics, where the various biological and chemical processes remain stable over time.

Biofouling – Accumulation of organisms on wet surfaces that can affect their functioning.

Biological filter (biofilter) – The component of the treatment units of an aquaculture system in which organic pollutants are decomposed (mainly oxidized) as a result of microbiological activity. The most important processes are the degradation of nitrogen metabolites by heterotrophic bacteria and the oxidation of ammonia via nitrite to nitrate.

Biomass ratio – The optimal balance between the fish and plants to obtain good fish and vegetable growth. It is expressed as the plant growing area that can be supported given a certain feeding rate.

Buffering (acid binding capacity) – The capacity of a solution containing a weak base and its conjugated acid to resist falls in pH when small quantities of an acid are added. The buffering occurs within a specific pH range and capacity that depends on the amount of alkali present in the solution. In aquaponics, the buffering occurs with carbonate or bicarbonate ions binding hydrogen ions from nitric acid until they all become saturated into carbonic acid, their weak conjugated acid form.

Carnivore – An animal that feeds mainly on the tissues of other animals.

Clarifier – A sedimentation tank built to remove suspended solids from the water by means of settling or separation from the aqueous media.

 

Chelate – A molecular association of a metal ion and a larger ligand, typically making the ion more soluble and biologically available.

Denitrification – The biochemical reduction of nitrate via the intermediate nitrite to molecular (gaseous) nitrogen and carbon dioxide through microbiological activity. In aquaculture: a necessary water treatment process in recycling systems from nitrogen buildup with little or no water exchange; also occurs in settling tanks, suspended solid traps, and water storage tanks.

Feed rate ratio – The ratio that helps balance an aquaponics system, relating the amount of feed added to the amount of plant growing area.

Flood and drain – A method controlling the water flow in a hydroponic or aquaponic grow bed where the media is alternatively submerged and drained with water, which ensures both adequate aeration of the plant roots and bacterial colonies while distributing water and nutrients equally. Also known as ebb and flow.

Footprint – A resource-measuring tool to determine the amount of land or water needed to support with resources a community or an activity and to assimilate the waste produced. Higher sustainability is obtained when a smaller footprint is required to obtain the same product by using a different technology or to support a community by adopting more sound management.

Granulometry – A description of the size classes in a group of granular material with implications for surface area to volume ratio.

Hardness – Measure of the concentrations of dissolved ions of calcium and magnesium in the water. Hardness is expressed as equivalent of calcium carbonate in milligrams per litre (mg/litre). Hardness can be also expressed as milliequivalent per litre, German hardness (°dH) or mg/litre of calcium oxide (CaO) according to the following conversion factor: 50 mg/litre CaCO3 = 1 meq/litre = 2.805 (°dH) = 28 mg/litre CaO.

Head, head pressure – In hydraulics: the measurement of pressure of water expressed in height at which water is held or can rise to, allowing it to flow to lower levels, push through pipes, etc.

Header tank – A water tank kept at a height for supplying water to lower rearing units, for example hatchery incubators and nursery tanks.

Herbivore – An animal that feeds mainly on plant material.

Hydroponics – A form of soil-less agriculture where plants are provided a nutrient solution containing all essential macronutrients and micronutrients necessary for growth, either through irrigation of inert media or directly within tanks of nutrient solution.

Ion – An atom or radical with an electrical charge that is positive (cation) or negative (anion) as a result of having lost or gained electrons.

Molecular nitrogen – An odourless gaseous element that makes up 78 percent of the Earth’s atmosphere, and is a constituent of all living tissue. It is almost inert in its gaseous form.

New tank syndrome – A common condition in newly installed aquaculture and aquarium systems with insufficient or immature biofiltration capabilities resulting in accumulation of toxic ammonia and nitrite, causing fish stress and ultimate death.

Nitrification – The aerobic bacterial conversion (oxidation) of ammonia and organic nitrogen to stable salts (nitrates), via bacteria, often Nitrosomonas spp. and Nitrobacter spp.

Nitrogen-fixation – The process by which certain bacteria and cyanobacteria are able to convert atmospheric nitrogen into combined forms into the soil, making them available to plants.

 

Nutrient cycle (nitrogen cycle) – Biogeochemical cycle, in which inorganic nutrients move through the soil, living organisms, air, and water. In agriculture, it refers to the return back to the soil of nutrients absorbed by plants from the soil. Nutrient cycling can take place through leaf fall, root exudation (secretion), residue recycling, incorporation of green manures, etc.

Nutrient lockout (pH-dependent nutrient availability) – An effect of pH and soil chemistry on the bioavailability of nutrients to be absorbed by plants, especially important in hydroponics and aquaponics. Each nutrient has a pH range in which it is available, but outside this range, the plants will not be able to use the nutrients despite their presence in the nutrient solution.

Omnivore – An animal that consumes both plant and animal material.

Oxidation – Type of chemical reaction, always coupled with reduction, in which the molecule in question loses an electron, often binding with oxygen. Examples include the burning of wood or the rusting of iron.

Photoperiodism – The physiological response of plants and animals to the seasonal length of days and nights. In plants, the presence of photoreceptors informs the plants of the optimal period to flower. Photoperiodic plants can start their flowering either with long or short days depending on the species. In animals, photoperiodism together with temperature regulate the physiological changes in sexual behaviour, migration, and hibernation.

Reduction – Type of chemical reaction, always coupled with oxidation, in which the molecule in question gains an electron, often losing an oxygen molecule, atom, or ion.

Soil-less agriculture (hydroponics) – The growing of plants without soil. Plants are fed with an aerated solution of nutrients, and the roots are either supported within an inert matrix or are freely floating in the nutrient solution.

Soil tiredness – A condition in soils that lead to a progressive reduction in yields after repeated cultivation of the same crop on the same area. The condition is due to a combination of nutrient depletion, exploitation of soil structure (low organic matter), accumulation of pathogens (parasites, pests, bacteria, fungi) specifically targeting the crop, selection of species-specific weeds, and accumulation of inhibiting root exudates.

Soluble – The ability of a substance to be dissolved in water or other liquid media, typically dependent on the charge and size of its molecules and the charge of the liquid. The more uncharged and the larger the molecules are, the less soluble in water is the substance.

Specific surface area – A metric to describe how much surface area is exposed for each unit of volume of an object alone or in a set. The value provides an indirect reading of porosity and granulometry of an object and is especially important for chemical reaction and biological activity, with a high ratio providing more area for the action in question.

Stocking density – Usually an expression of the number of fish per unit area or weight of fish per unit of volume of water at stocking.

Stress – The sum of biological reactions to any adverse stimuli (physical, internal, or external) that disturb the organism’s optimum operating status and may reduce its chances of survival.

Sustainable development – Management and conservation of the natural resource base, and the orientation of technological and institutional change in such a manner as to ensure the attainment of continued satisfaction of human needs for present and future generations. Such sustainable development conserves land, water, plants, and animal genetic resources, is environmentally non-degrading, technologically appropriate, economically viable, and socially acceptable.

 

System cycling – Initial development of a biofilter within an aquaculture or aquarium system as the tank and biofilter material are colonized by ammonia-oxidizing bacteria and nitrite-oxidizing bacteria. These groups of bacteria oxidize the original source of ammonia into nitrite and nitrate, respectively. It usually takes between one and six weeks depending on temperature, water quality, and ammonia source. Adequate system cycling reduces the effects of new tank syndrome.

Turnover rate – In culture systems such as tanks, raceways, ponds, and other units, this term refers to the real water exchange rate over a period of time defined as the inverse of residence time: Q (water quantity, in m3/h) / V (unit volume, in m3).

Ultraviolet – Non-visible electromagnetic waves, which follow at the end of the violet end of the light spectrum. That part of the solar radiation spectrum between 40 nm and 400 nm wavelength. Used in aquaculture to disinfect water and prevent diseases caused by pathogenic microorganisms.

 

Appendixes Appendix 1 – Vegetable production guidelines for 12 common aquaponic plants 169 

 

Appendix 2 – Plant pests and disease control 183 

 

Appendix 3 – Fish pests and disease control 187 

 

Appendix 4 – Calculating the amount of ammonia and biofilter media for an aquaponic unit 191 

 

Appendix 5 – Making homemade fish feed 193 

 

Appendix 6 – Key considerations before setting up an aquaponic system 199 

 

Appendix 7 – Cost-benefit analysis for small-scale aquaponic units 205 

 

Appendix 8 – Step-by-step guide to constructing small-scale aquaponic systems 209

 

Appendix 1 – Vegetable production guidelines for 12 common aquaponic plants 

 

The information below provides technical advice on 12 of the most popular vegetables to grow in aquaponics. Information on optimal growing conditions, including specific growing instructions and harvesting techniques for each vegetable, is included. The guidelines below are based on the experience gathered from long-standing aquaponic farming, from horticulture manuals on soil/soil-less cropping, extension papers, and the professional experience of farmers and researchers. This list is by no means exhaustive. Rather, it should be used as an example of the types of information needed for any crop grown and help readers target their research when growing crops that are not listed here. Other common crops, not included in this appendix are: okra, pak choy, bok choy, ong choy, tatsoi, kale, mint, thyme, dill, scallions, chives, cilantro, taro, watercress, salad rocket, edible flowers, ornamental flowers, and even small fruit trees. Root vegetables such as onion, carrot, beets, radish and taro should be grown in wicking beds attached to media beds.

 

BASIL 

pH: 5.5–6.5 

Plant spacing: 15–25 cm (8–40 plants/m2 ) 

Germination time and temperature: 6–7 days with temperatures at 20–25 °C 

Growth time: 5–6 weeks (start harvesting when plant is 15 cm) 

Temperature: 18–30 °C, optimal 20–25 °C 

Light exposure: Sunny or slightly sheltered 

Plant height and width: 30–70 cm; 30 cm 

Recommended aquaponic method: media beds, NFT and DWC

 

Growing basil in aquaponic units: 

Basil is one of the most popular herbs to grow in aquaponic units, particularly in large-scale commercial monoculture units because of its high value and the high demand in urban or peri-urban zones. Many cultivars of basil have been tried and tested in aquaponic units including the Italian Genovese basil (sweet basil), lemon basil, and purple passion basil. Owing to the higher nitrogen uptake, basil is an ideal plant for aquaponics; however, care should be used to avoid excessive nutrient depletion of the water.

 

Growing conditions: 

Basil seeds need a reasonably high and stable temperature to initiate germination (20–25  °C). Once transplanted in the units, basil grows best in warm to very warm conditions and full exposure to sun. However, better quality leaves are obtained through slight shading. With daily temperatures higher than 27 °C plants should be ventilated or covered with shading nets (20  percent) during strong solar radiation seasons to prevent tip burn.

 

Growing instructions: 

Transplant new seedlings into the aquaponic unit when the seedlings have 4–5 true leaves. Basil can be affected by various fungal diseases, including Fusarium wilt, grey mould, and black spot, particularly under suboptimal temperatures and high humidity conditions. Air ventilation and water temperatures higher than 21 °C, day and night, help to reduce plant stress and incidence of diseases.

 

Harvesting: 

The harvest of leaves starts when plants reach 15  cm in height and continues for 30–50  days. Care should be used when handling leaves at harvest to avoid leaf bruising and blackening. It is advisable to remove flowering tips during plant growth to avoid bitter tastes in leaves and encourage branching. However, basil flowers are attractive to pollinators and beneficial insects, so leaving a few flowering plants can improve the overall garden and ensure a constant supply of basil seeds. Basil seeds are a speciality product in some locations.

 

CAULIFLOWER 

pH: 6.0–6.5 

Plant spacing: 45–60 cm (3–5 plants/m2 ) 

Germination time and temperature: 4–7 days with temperature 8–20 °C 

Growth time: 2–3 months (spring crops), 3–4 months (autumn crops) 

Temperature: 20–25  °C for initial vegetative growth, 10–15  °C for head setting (autumn crop) 

Light exposure: full sun Plant height and width: 40–60 cm; 60–70 cm Recommended aquaponic method: media beds

Growing cauliflower in aquaponic units: 

Cauliflower is a high-value, nutritious winter crop that will grow and thrive in media bed units with adequate plant spacing. Cauliflower has a relatively high nutrient demand, and the plants react positively to high concentrations of nitrogen and phosphorus. Among other nutrients, potassium and calcium are important for the production of heads. The plant is particularly sensitive to climatic conditions, and the heads do not develop properly in hot, very cold or very dry conditions; therefore, selecting the suitable variety and the timing to transplant are crucial.

 

Growing conditions: 

Optimal air temperature for the initial vegetative growth of the plant is 15–25 °C. For the formation of the heads, the plants require colder temperatures of 10–15 °C (autumn crop) or 15–20 °C (spring crop) providing that a good percentage of relative humidity and full sun conditions are met to develop good heads. Plants can tolerate cold temperatures; however, heads can be damaged by frost. Light shade can be beneficial in warmer temperatures (above 23 °C).

 

Growing instructions: 

Germinate seeds in propagation trays at 20–25  °C. Provide direct sun from early seedling stages so plants do not become leggy. When plants are 3–5 weeks old and have 4–5 true leaves, begin transplanting into the aquaponic system about 50 cm apart. To preserve the white colour of the heads, use string or rubber bands to secure outside leaves over the head when it is about 6–10 cm in diameter. Once this stage is reached, harvest may take less than a week in ideal temperatures or as long as a month in cooler conditions. Too much sun, heat or nitrogen uptake can cause “ricey” heads where the main flower separates into small, rice-like grains. Temperatures below 12  °C could instead produce “buttoning”. Cauliflower is susceptible to some pests including cabbageworms, flea beetle, white maggots (larvae) and cabbage aphids, which can be removed manually or by using other pest management techniques.

 

Harvesting: 

Harvest when the heads are compact, white and firm. Cut the heads off the plant with a large knife, and remove the remaining plant and roots from the bed pipe and place into a compost bin.

 

LETTUCE (MIXED SALAD LEAVES): 

pH: 6.0–7.0 

Plant spacing: 18–30 cm (20–25 heads/m2 ) 

Germination time and temperature: 3–7 days; 13–21 °C 

Growth time: 24–32 days (longer for some varieties) 

Temperature: 15–22 °C (flowering over 24 °C) 

Light exposure: full sun (light shading in warm temperatures) 

Plant height and width: 20–30 cm; 25–35 cm 

Recommended aquaponic method: media bed, NFT and DWC

 

Growing lettuce in aquaponic units: 

Lettuce grows particularly well in aquaponics owing to the optimal nutrient concentrations in the water. Many varieties can be grown in aquaponics, but four main types are included here: crisphead lettuce (iceberg), which has tight head with crispy leaves, ideal for cooler conditions; butterhead lettuce, which show leaves that are loosely piled one on another and have no bitter taste; Romaine lettuce, which has upright and tightly folded leaves that are slow to bolt and are sweet in taste; and loose leaf lettuce, which comes out in a variety of colours and shapes with no head and can be directly sowed on media beds and harvested by picking single leaves without collecting the whole plant. Lettuce is in high demand and has a high value in urban and peri-urban zones, which makes it a very suitable crop for large-scale commercial production.

 

Growing conditions: 

Lettuce is a winter crop. For head growth, the night air temperature should be 3–12 °C, with a day temperature of 17–28 °C. The generative growth is affected by photoperiod and temperature  – extended daylight and warm conditions (>  18  °C) at night cause bolting. Water temperature >  26  °C may also favour bolting and leaf bitterness. The plant has low nutrient demand; however, higher calcium concentrations in water help to prevent tip burn in leaf in summer crops. The ideal pH is 5.8–6.2, but lettuce still grows well with a pH as high as 7, although some iron deficiencies might appear owing to reduced bio-availability of this nutrient above neutrality.

 

Growing instructions: 

Seedlings can be transplanted in aquaponic units at three weeks when plants have at least 2–3 true leaves. Supplemental fertilization with phosphorus to the seedlings in the second and third weeks favours root growth and avoids plant stress at transplant. Moreover, plant hardening, through exposing of seedlings to colder temperatures and direct sunlight, for 3–5  days before transplanting results in higher survival rates. When transplanting lettuce in warm weather, place light sunshade over the plants for 2–3 days to avoid water stress. To achieve crisp, sweet lettuce, grow plants at a fast pace by maintaining high nitrate levels in the unit. When air and water temperatures increase during the season, use bolt-resistant (summer) varieties. If growing in media beds, plant new lettuces where they will be partially shaded by taller nearby plants.

 

Harvesting: 

Harvesting can begin as soon as heads or leaves are large enough to eat. If selling to markets, remove the full plants and roots when harvesting as soon as they reach market weight (250–400 g). Cut the roots out and place them in a compost bin. Harvest early in the morning when leaves are crisp and full of moisture and chill quickly.

 

CUCUMBERS 

pH: 5.5–6.5 

Plant spacing: 30–60 cm (depending on variety; 2–5 plants/m2 ) 

Germination time and temperature: 3–7 days; 20–30 °C 

Growth time: 55–65 days 

Temperature: 22–28 °C day, 18–20 °C night; highly susceptible to frost. 

Light exposure: full sun 

Plant height and width: 20–200 cm; 20–80 cm 

Recommended aquaponic method: media beds; DWC 

 

Growing cucumbers in aquaponic units: 

Cucumbers, along with other members of the Cucurbitaceae family including squash, zucchini and melons, are excellent highvalue summer vegetables. They are ideal plants to grow in media bed units as they have a large root structure. Cucumbers can also be grown on floating rafts, although in grow pipes there could be the risk of clogging owing to excessive root growth. Cucumbers require large quantities of nitrogen and potassium, thus the choice for the number of plants should take into account the nutrients available in the water and the fish stocking biomass.

 

Growing conditions: 

Cucumbers grow best with long hot humid days with ample sunshine and warm nights. Optimal growth temperatures are 24–27 °C during the day with 70–90 percent of relative humidity. A temperature of the substrate of about 21 °C is also optimal for production. Plants stop their growth and production at 10–13 °C. It is recommended to have higher potassium concentration to favour higher fruit settings and yields. 

 

Growing instructions: 

Cucumbers seedlings can be transplanted at 2–3 weeks at the 4–5 leaf stage. Plants grow very quickly and it is a good practice to limit their vegetative vigour and divert nutrients to fruits by cutting their apical tips when the stem is two metres long; removing the lateral branches also favours ventilation. Further plant elongation can be successively secured by leaving only the two farthest buds coming out from the main stem. Plants are encouraged to further production by regular harvesting of fruits of marketable size (> 180 g for slicing varieties). The presence of pollinating insects is necessary for good fecundation and fruit set. Cucumber plants need support for their growth, which will also provide plants with adequate aeration to prevent foliar diseases (powdery mildew, grey mould). Owing to the high incidence of pest occurrences in cucumber plants, it is important to plan appropriate integrated pest management strategies (see Chapter 6) and to intercrop the plant unit with plants that are less affected by the possible treatments used.

 

Harvesting: 

Once transplanted, cucumbers can start production after 2–3  weeks. In optimal conditions, plants can be harvested 10–15 times. Harvest every few days to prevent the fruits from becoming overly large and to favour the growth of the following ones.

 

EGGPLANT 

pH: 5.5–7.0 

Plant spacing: 40–60 cm (3–5 plants/m2 ) 

Germination time and temperature: 8–10 days; 25–30 °C 

Growth time: 90–120 days 

Temperature: 15–18 °C night, 22–26 °C day; highly susceptible to frost Light exposure: full sun 

Plant height and width: 60–120 cm; 60–80 cm 

Recommended aquaponic method: media beds

 

Growing eggplant in aquaponic units: 

 

Eggplant is a summer fruiting vegetable that grows well in media beds owing to the deep growth of the root systems. Plants can produce 10–15  fruits for a total yield of 3–7  kg. Eggplants have high nitrogen and potassium requirements, which indicates the need for careful management choices in the number of plants to grow in each aquaponic unit in order to avoid nutrient imbalances.

 

Growing conditions: 

Eggplants enjoy warm temperatures with full sun exposure. Plants perform best with daily temperatures in the range of 22–26  °C and relative humidity of 60–70  percent, both of which favour strong fruit set. Temperatures < 9–10 °C and > 30–32 °C are very limiting. 

 

Growing instructions: 

Seeds germinate in 8–10 days in warm temperatures (26–30 °C). Seedlings can be transplanted at 4–5  leaves. Plants can be transplanted when temperatures rise in spring. Towards the end of the summer season, begin pinching off new blossoms to favour the ripening of the existing fruit. At the end of the season, plants can be drastically pruned at 20–30  cm by leaving just three branches. This method interrupts the crop without removing the plants during the unfavourable season (winter, summer) and lets the crop restart the production afterwards. Plants can be grown without pruning; however, in limited spaces or in greenhouses, management of the branches can be facilitated with stakes or vertical strings. 

 

Harvesting: 

 

Start harvesting when the eggplants are 10–15 cm long. The skin should be shiny; dull and yellow skin is a sign that the eggplant is overripe. Delayed harvest makes the fruits unmarketable owing to the presence of seeds inside. Use a sharp knife and cut the eggplant from the plant, leaving at least 3 cm of the stem attached to the fruit.

 

PEPPERS 

pH: 5.5–6.5 

Plant spacing: 30–60 cm (3–4 plants/m2 , or more for small-sized plant varieties) Germination time and temperature: 8–12 days; 22–30 °C (seeds will not germinate below 13 °C) 

Growth time: 60–95 days Temperature: 14–16 °C night time, 22–30 °C daytime Light exposure: full sun 

Plant height and width: 30–90 cm; 30–80 cm 

Recommended aquaponics method: media beds 

 

Growing peppers in aquaponic units: 

There are many varieties of peppers, all varying in colour and degree of spice, yet from the sweet bell pepper to the hot chili peppers (jalapeño or cayenne peppers) they can all be grown with aquaponics. Peppers are more suited to the media bed method but they might also grow in 11 cm diameter NFT pipes if given extra physical support.

 

Growing conditions: 

Peppers are a summer fruiting vegetable that prefers warm conditions and full sun exposure. Seed germination temperatures are high: 22–34 °C. Seeds will not germinate well in temperatures <  15  °C. Daytime temperatures of 22–28  °C and night-time temperatures of 14–16  °C favour best fruiting conditions under a relative humidity of 65–60  percent. Optimal temperatures at root level are 15–20 °C. In general, air temperatures below 10–12 °C stop plant growth and cause abnormal deformation of the fruits, making them unmarketable. Temperatures > 30–35 °C lead to floral abortion or fallout. In general, spicier peppers can be obtained at higher temperatures. The top leaves of the plant protect the fruit hanging below from sun exposure. As with other fruiting plants, nitrate supports the initial vegetative growth (optimum range: 20–120 mg/litre) but higher concentrations of potassium and phosphorus are needed for flowering and fruiting.

 

Growing instructions: 

Transplant seedlings with 6–8 true leaves to the unit as soon as night temperatures settle above 10 °C. Support bushy, heavy-yielding plants with stakes or vertical strings hanging from iron wires pulled horizontally above the units. For red sweet peppers, leave the green fruits on the plants until they ripen and turn red. Pick the first few flowers that appear on the plant in order to encourage further plant growth. Reduce the number of flowers in the event of excessive fruit setting to favour the growing fruits to reach adequate size. 

 

Harvesting: 

Begin harvesting when peppers reach a marketable size. Leave peppers on the plants until they ripen fully by changing colour and improve their levels of vitamin C. Harvest continually through the season to favour blossoming, fruit setting and growth. Peppers can be easily stored fresh for 10 days at 10 °C with 90–95 percent humidity, or they can be dehydrated for long-term storage.

 

TOMATO 

pH: 5.5–6.5 

Plant spacing: 40–60 cm (3–5 plants/m2 ) 

Germination time and temperature: 4–6 days; 20–30 °C Growth time: 50–70 days till first harvest; fruiting 90–120 days up to 8–10 months (indeterminate varieties) 

Optimal temperatures: 13–16 °C night, 22–26 °C day 

Light exposure: full sun 

Plant height and width: 60–180 cm; 60–80 cm 

Recommended aquaponic method: media beds and DWC 

 

Growing tomatoes in aquaponic units: 

Tomatoes are an excellent summer fruiting vegetable to grow using all methods of aquaponics, although physical support is necessary. Given the high nutrient demand of tomatoes, especially potassium, the number of plants per unit should be planned according to the fish biomass, in order to avoid nutrient deficiencies. A higher nitrogen concentration is preferable during early stages to favour plants’ vegetative growth; however, potassium should be present from the flowering stage to favour fruit settings and growth.

 

Growing conditions: 

Tomatoes prefer warm temperatures with full sun exposure. Below 8–10 °C the plants stop growing, and night temperatures of 13–14 °C encourage fruit set. Temperatures above 40  °C cause floral abortion and poor fruit setting. There are two major types of tomato plants: determinate (seasonal production) and indeterminate (continuous production of floral branches). In the first type, plants can be left to grow as bushes by leaving 3–4  main branches and removing all the auxiliary suckers to divert nutrients to fruits. Both determinate and indeterminate varieties should be grown with a single stem (double in case of high plant vigour) by removing all the auxiliary suckers. However, in determinate varieties, the apical tip of the single stem has to be cut as soon as the plant reaches 7–8 floral branches in order to favour fruiting. Tomato rely on supports that can be either made of stakes (bush plants) or bound to vertical plastic/nylon strings that are attached to iron wires pulled horizontally above the plant units. Tomatoes have a moderate tolerance to salinity, which makes them suitable for areas where pure freshwater is not available. Higher salinity at fruiting stage improves quality of the products.

 

Planting instructions: 

Set stakes or plant support structures before transplanting to prevent root damage. Transplant the seedlings into units 3–6 weeks after germination when the seedling is 10–15 cm and when night-time temperatures are constantly above 10 °C. In transplanting the seedlings, avoid waterlogged conditions around the plant collar to reduce any risks of diseases. Once the tomato plants are about 60 cm tall, start to determine the growing method (bush or single stem) by pruning the unnecessary upper branches. Remove the leaves from the bottom 30 cm of the main stem to favour a better air circulation and reduce fungal incidence. Prune all the auxiliary suckers to favour fruit growth. Remove the leaves covering each fruit branch soon before ripening to favour nutrition flow to the fruits and to accelerate maturation.

 

Harvesting: 

For best flavour, harvest tomatoes when they are firm and fully coloured. Fruits will continue to ripen if picked half ripe and brought indoors. Fruits can be easily maintained for 2–4 weeks at 5–7 °C under 85–90 percent relative humidity.

 

BEANS AND PEAS 

pH: 5.5–7.0 

Plant spacing: 10–30  cm dependent on variety (bush varieties 20–40  plants/m2 , climbing varieties 10–12 plants/m2 ) 

Germination time and temperature: 8–10 days; 21–26 °C 

Growth time: 50–110 days to reach maturity depending on variety 

Temperature: 16–18 °C night, 22–26 °C day 

Light exposure: full sun 

Plant height and width: 60–250 cm (climbing); 60–80 cm (bush) 

Recommended aquaponic method: media bed

 

Growing beans in aquaponic units: 

Both climbing and bush bean varieties grow well in aquaponic units, but the former are recommended for less use of space, which maximizes aquaponic bed use. Climbing varieties can also yield 2–3  times more pods than bush varieties. Beans have low nitrate needs, but have a moderate demand in terms of phosphorus and potassium. Such nutrient requirements make beans an ideal choice for aquaponic production, although excess nitrate may delay flowering. Beans are recommended for newly established units as they may fix atmospheric nitrogen on their own.

 

Growing conditions for pole beans: 

Climbing varieties enjoy full sun, but will tolerate partial shade in warm conditions. Plants do not grow at <  12–14  °C. Temperatures > 35 °C cause floral abortion and poor fruit set. Optimal relative humidity for plants is 70–80 percent. Beans are sensitive to the photoperiod; thus, it is important to choose the right varieties according to the location and season. In general, climbing varieties are cultivated in summer while dwarf varieties are adapted to short-day conditions (spring or autumn).

Growing instructions for pole beans: 

For media bed units, seed directly into the grow bed 3–4  cm deep (making sure the bell siphon is out so the water level is high during germination). Beans do not transplant well, which makes them hard to grow in NFT pipes. Any supporting pole should be placed before seed germination in order to avoid root damage. In sowing, care should be taken to avoid future cross-shading with other plants. Beans are susceptible to aphids and spider mites. Although low occurrences of such pests could be controlled with mechanical remedies, attention should be paid to the choice of companion plants to avoid cross-contamination if any treatment has to be carried out.

 

Harvesting: 
Snap bean varieties (green or yellow wax beans) – 

Pods should be firm and crisp at harvest; the seeds inside should be undeveloped or small. Hold stem with one hand and pod with the other to avoid pulling off branches that will produce later pickings. Pick all pods to keep plants productive.

 

Shell beans (black, broad or fava beans) – 

Pick these varieties when the pods change colour and the beans inside are fully formed but not dried out. Pods should be plump, firm. Quality declines if they are left on the plant for too long.

 

Dried beans (kidney beans and soybeans) – 

Let the pods become as dry as possible before cooler weather sets in or when plants have turned brown and lost most of their leaves. Pods will easily split when very dry, making seed removal an easy process.

 

HEAD CABBAGE 

pH: 6–7.2 

Plant spacing: 60–80 cm (4–8 plants/m2 ) 

Germination time and temperature: 4–7 days; 8–29 °C 

Growth time: 45–70 days from transplanting (depending on varieties and season) 

Ideal temperature: 15–20 °C (growth stops at > 25 °C) 

Light exposure: full sun Plant height and width: 30–60 cm; 30–60 cm 

Recommended aquaponic method: media beds (not suitable for newly established aquaponic units)

 

Growing cabbage in aquaponic units: 

Cabbage is a highly nutritious winter crop. The plants grow best in media beds because they reach significant dimensions at harvest and may be too large and heavy for rafts or grow pipes. Cabbage is a nutrient-demanding plant, which makes it unsuitable for newly established units (less than four months old). Nevertheless, owing to the large space required, cabbage crops take up fewer nutrients per square metre than other winter leafy vegetables (lettuce, spinach, rocket, etc.). Although cabbage can tolerate temperatures as low as 5 °C, the low temperatures may not be suitable for culturing fish.

 

Growing conditions: 

Cabbage is a winter crop with ideal growing temperatures of 15–20  °C; Cabbage grows best when the heads mature in cooler temperatures, so plan to harvest before daytime temperatures reach 23–25 °C. High concentrations of phosphorus and potassium are essential when the heads begin to grow. Integration with organic fertilizers delivered either on leaves or substrates may be necessary in order to supply plants with adequate levels of nutrients.

 

Growing instructions: 

Transplant seedlings at 4–6  leaves and a height of 15  cm. Position seedlings with an optimal planting density according to the chosen variety. In the event of day temperatures > 25 °C, use a shading net of 20 percent light shading to prevent the plant from bolting (growing to produce seeds). Given the high incidence of cabbage worms and other pests such as aphids, root maggots and cabbage loopers, it is important to carry out careful monitoring and use organic (aquaponic safe) pesticides when necessary.

 

Harvesting: 

Start harvesting when cabbage heads are firm with a diameter of about 10–15  cm (depending on variety grown). Cut the head from the stem with a sharp knife, and place the outer leaves into the compost bin. If cabbage heads tend to break, it indicates they are over-ripe and should have been harvested earlier.

 

BROCCOLI 

pH: 6–7 

Plant spacing: 40–70 cm (3–5 plants/m2 ) 

Germination time and temperature: 4–6 days; 25 °C 

Growth time: 60–100 days from transplant 

Average daily temperature: 13–18 °C 

Light exposure: full sun; can tolerate partial shade but will mature slowly 

Plant height and width: 30–60 cm; 30–60 cm 

Recommended aquaponic method: media beds.

 

Growing broccoli in aquaponic units: 

Broccoli is a nutritious winter vegetable. The media bed method is the recommended option as broccoli is a large and heavy plant at harvest. Broccoli is moderately difficult to grow because it is a nutrient-demanding plant. It is also highly susceptible to warm temperatures; therefore, select a variety that is bolt-resistant. 

 

Growing conditions: 

Broccoli grows best when daytime temperatures are 14–17 °C. For head formation, winter varieties require temperatures of 10–15  °C. Higher temperatures are possible, providing that a higher humidity is present. Hot temperatures cause premature bolting. 

 

Growing instructions: 

Transplant seedlings into media beds once 4–5 true leaves are present and the plants are 15–20 cm high. Seedlings should be positioned 40–50 cm apart as closer spacing will produce smaller central heads. Broccoli, as well as cabbage, is susceptible to cabbage worms and other persistent pests. While some mechanical removal can have marginal effect, treatment with biological pesticides and repellents can control the infestations. 

 

Harvesting: 

For best quality, begin harvesting broccoli when the buds of the head are firm and tight. Harvest immediately if the buds start to separate and begin flowering (yellow flowers).

 

SWISS CHARD / MANGOLD 

pH: 6–7.5 

Plant spacing: 30–30 cm (15–20 plants/m2 ) 

Germination time and temperature: 4–5 days; 25–30 °C optimal 

Growth time: 25–35 days 

Temperature: 16–24 °C 

Light exposure: full sun (partial shade for temperatures > 26 °C) P

lant height and width: 30–60 cm; 30–40 cm 

Recommended aquaponic method: media beds, NFT pipes and DWC

 

Growing Swiss chard in aquaponic units: 

Swiss chard is an extremely popular leafy green vegetable to grow using aquaponics and it thrives with all three aquaponic methods. It is a moderate nitrate feeder and requires lower concentrations of potassium and phosphorus than fruiting vegetables, which makes it an ideal plant for aquaponics. Owing to its high market value, its fast growth rate and its nutritional content, Swiss chard is frequently grown in commercial aquaponic systems. Foliage is green to dark green, but the stems can have striking and attractive colours of yellow, purple or red. 

 

Growing conditions: 

Swiss chard optimal temperatures are 16–24  °C, while the minimum temperature for growth is 5 °C. Although traditionally a late-winter/spring crop (tolerating moderate frosts), Swiss chard may also grow well in full sun during mild summer seasons. A shading net is suggested at higher temperatures. Swiss chard has a moderate tolerance to salinity, which makes it an ideal plant for saline water.

 

Growing instructions: 

Swiss chard seeds produce more than one seedling; therefore, thinning is required as the seedlings begin to grow. As plants become senescent during the season, older leaves can be removed to encourage new growth. 

 

Harvesting: 

Swiss chard leaves can be continuously cut whenever they reach harvestable sizes. The removal of larger leaves favours the growth of new ones. Avoid damaging the growing point in the centre of the plant at harvest.

 

PARSLEY 

pH: 6–7 

Plant spacing: 15–30 cm (10–15 plants/m2 ) 

Germination time and temperature: 8–10 days; 20–25 °C 

Growth time: 20–30 days after transplant 

Temperature: 15–25 °C 

Light exposure: full sun; partial shade at > 25 °C 

Plant height and width: 30–60 cm; 30–40 cm 

Recommended aquaponic method: media beds, NFT and DWC

 

Growing parsley in aquaponic units: 

Parsley is a very common herb grown in both domestic and commercial aquaponic units owing to its nutritional content (rich in vitamins A and C, calcium and iron) and its high market value. Parsley is an easy herb to grow as the nutrient requirements are relatively low compared with other vegetables. 

 

Growing conditions: 

Parsley is a biennial herb but it is traditionally grown as an annual; most varieties will grow over a two-year period if the winter season is mild with minimal to moderate frost. Although the plant can resist temperatures of 0 °C, the minimum temperature for growth is 8 °C. In the first year, the plants produce leaves while in the second the plants will begin sending up flower stalks for seed production. Parsley enjoys full sun for up to eight hours a day. Partial shading is required for temperatures > 25 °C.

 

Growing instructions: 

The main difficulty when growing parsley is the initial germination, which can take 2–5  weeks, depending on how fresh the seeds are. To accelerate germination, seeds can be soaked in warm water (20–23 °C) for 24–48 hours to soften the seed husks. Afterwards, drain the water and sow the seeds into propagations trays. Emerging seedlings will have the appearance of grass, with two narrow seed leaves opposite each other. After 5–6 weeks, transplant the seedlings into the aquaponic unit during early spring. 

 

Harvesting: 

Harvesting begins once the individual stalks of the plant are at least 15 cm long. Harvest the outer stems from the plant first as this will encourage growth throughout the season. If only the top leaves are cut, the stalks will remain and the plant will be less productive. Parsley dries and freezes well. If dried, plants can be crushed by hand and stored in an airtight container.

 

Appendix 2 – Plant pests and disease control 

Aquaponic pest management can benefit from most of the common biological methods used in organic agriculture. However, it is important to remember that a strategy against pests should be planned according to the insects occurring in that particular area and the crop being cultivated during a specific season and a given environment.

 

PEST CONTROL: REPELLENTS, SOFT-CHEMICALS AND PLANT-DERIVED INSECTICIDES 

Soft-chemical alternatives to industrial pesticides can also be applied to deter pests. Organic mixes consisting of crushed garlic, pepper, soap and insecticidal oils can all be used to remove the threat of pests. If using soaps, make sure to use natural soaps, otherwise potentially harmful chemicals typically found in synthetic soaps can make their way into the water. Soaps can damage fish gills, so care should be used not allow too much to enter the water. Thorough coverage of the plant is necessary for effective pest control. Although observed and empirical knowledge on many of these methods suggests they work, there has not been systematic scientific research on their efficacy. Moreover, the medicinal properties of vegetables extracts used would suggest caution in their use because of toxicity risks to the fish.

 

PEST CONTROL: INSECTICIDES, PLANT-DERIVED 

Biological insecticides deserve particular attention in aquaponics as not all of them are suitable for fish. Although biological insecticides are classified for organic use, most of them are toxic to fish and to beneficial insects. The table below listed a number of common insecticides and critical information for their safe use.

 

PEST CONTROL: BENEFICIAL INSECTS 

Beneficial insects can be used to control pests. This method is more applicable for large producers, as the cost can be prohibitive on a small-scale. The choice of insect must be matched to the pest insect and environmental conditions. 

 

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DISEASE CONTROL: ENVIRONMENTAL 

 

Many fungal diseases are dependent of temperature and humidity, and as such, controlling the environmental factors can mitigate the disease. If the environmental factors cannot be controlled, it may be better to choose resistant crops or varieties. 

 

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DISEASE CONTROL: INORGANIC CHEMICAL 

 

Some inorganic compounds can be used to treat fungal diseases, and many of these are acceptable to use in aquaponic units. The table below outlines a few of these options.

 

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COMPANION PLANTING CHART 

 

Companion planting is a small-scale intercropping method that is very common in organic and biodynamic horticulture. The justifying theory is that the association of different plants has either a mechanical, repellent or dissuasive effect against pests. In addition, some beneficial effects on the complex soil/plant agro-ecosystem can be encouraged by the release of substances or root exudates from beneficial plants. Although some degree of pest control has been scientifically verified, the degree of success depends on: the level of pest infestation, the crop density, the ratio between crops and beneficial plants, and the specific planting times. Companion planting can be used in combination with other strategies within an integrated plant and pest management to obtain healthier crops in aquaponic systems. The table below gives a general overview of possible combinations according to biodynamic principles. Specific information can be obtained easily from the detailed literature available on organic and biodynamic agriculture.

 

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Appendix 3 – Fish pests and disease control

 

As discussed in Section 7.6.3, disease is the result of an imbalance between the fish, the pathogen/causative agent and the environment. Weakness in the animal and higher incidence of the pathogen in certain environmental conditions more favourable for the pathogen causes disease. Sound fish management practices that build a healthy immune system are the primary actions to secure a healthy stock. Fish diseases must be recognized and treated expediently. The following two tables outline symptoms and causes of common diseases, separated as abiotic and biotic, to highlight the importance of water quality and environmental conditions in disease identification.

 

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Appendix 4 – Calculating the amount of ammonia and biofilter media for an aquaponic unit 

 

This appendix provides detailed explanations on the optimal amount of filtration media required to convert the ammonia into nitrate from a given amount of fish feed. In addition to the information provided in Chapter 8 of the main text of this publication, it is important to introduce two new parameters in the equations:

 

  • total ammonia nitrogen (TAN) produced by fish feed
  • conversion rate of ammonia to nitrate by bacteria

 

DETERMINING THE AMOUNT OF AMMONIA PRODUCED BY FEED 

 

Ammonia is a by-product from the degradation of proteins. The amount of ammonia in the water depends on several factors, including the quantity/quality of proteins or amino acids in the feed, the digestibility, the fish species, the temperature, and the removal of fish wastes from the aquaponic system. On average, 30  percent of the proteins supplied by the diet are retained in the fishes’ body. Therefore, 70  percent of the nitrogen is lost: 15 percent is not digested, and exits as solid waste (faeces) and uneaten feed, while the remaining 55  percent is excreted by the fish as ammonia or products easily degradable into ammonia. In addition to the wastes directly dissolved, it is worth noticing that about 60  percent of the solid waste produced is taken out from the system by means of clarifiers or settlers, which leaves about 6 percent of the solid waste to be degraded into ammonia in the water. Overall, about 61 percent of the nitrogen from the feed becomes ammonia and is subject to nitrification. Take the example of 20 kg of fish eating 1 percent of their body weight per day (200  g of fish feed). From these 200  g of feed (32  percent protein), the amount of ammonia produced is approximately 7.5 grams. To achieve this result, first the amount of nitrogen is calculated based on the percentage of protein in the feed; and the amount of nitrogen contained in the protein (16 percent). Then, the amount of wasted nitrogen is calculated: 61  percent of the nitrogen is wasted (6 percent as undigested/uneaten feed retained into the system; 55 percent excreted by fish). For each gram of wasted nitrogen, 1.2 g of ammonia is produced, according to standard chemistry methods (not included here). The following equation shows the process: 

 

200 g feed 32 g protein 100 g feed 16 g nitrogen 100 g protein 61 g wasted nitrogen 100 g total nitrogen 1.2 g NH3 1 g nitrogen X X X X = 7.5 g ammonia

 

DETERMINING THE AMOUNT OF BIOFILTER MEDIA NEEDED BY NITRIFYING BACTERIA

 

 The ammonia removal rate by nitrifying bacteria is 0.2–2 g per square metre per day. The removal rate depends on the biofilter design, water load (amount of water flowing through the bacteria), temperatures (higher biological activity at >  20  °C), salinity, pH, oxygen as well as suspended solids from fish wastes. To simplify the complex calculations needed, a conservative rate is used: 0.57  g of ammonia is converted per square metre of surface area per day. Given a daily amount of feed of 200 g and the resulting production of 7.5 g of ammonia, it is necessary to provide bacteria with an operating surface area of 13.3 m2, as shown in the following equation:

 

7.5 g ammonia 1 m2 0.57 g ammonia 13.3 m2

 

The surface for bacteria can be obtained from a wide choice of materials, each with a specific surface area (SSA), also known as the surface area to volume ratio, expressed as square metres per cubic metre (m2 /m3 ). Common biofilter media include gravel, sand, fibre mesh pads and plastic filter medium. The SSA indicates the total surface that one cubic metre of a particular material would have if all its particles had their surface area measured. Some of these SSA values are recorded in Table A4.1 (see also Table 4.1). The volume of media required to convert the ammonia can be calculated using the SSA ratios. An example using volcanic tuff is provided in the following equation. Volcanic tuff has an SSA of 300 m2 /m3 . The volume of tuff needed to guarantee an operating surface of 13.3 m2 , calculated above, for nitrifying bacteria can be obtained with a simple division:

 

13.3 m2 1 m3 300 m2 0.0443 m3

 

The final volume of tuff required to process 200 g of feed per day is 0.0443 m3 . One cubic metre is equivalent to 1 000 litres, and therefore the volume of tuff required is 44.3 litres. Hence, 1 litre of tuff can convert the ammonia obtained by 4.5 g of feed.

 

44.3 litres tuff 200 g feed 1 litre tuff 4.5 g feed

 

When using media bed aquaponic techniques, the amount of media used for plant growing far exceeds the minimum amount required for biofiltration and conversion of ammonia. This results in a robust system in the event of a severe reduction of the efficiency of the nitrifying bacteria. The system design described in Appendix 8 of this publication has a tuff volume of 900  litres, almost 20  times higher than the volume needed to process the ammonia produced from 200 g of feed.

 

It is possible to use any biofilter medium and determine the volume needed by knowing the SSA. However, it is worth mentioning that the larger the SSA in the media is, the higher the risk of clogging if the water has some suspended solids, which can easily occur in overstocked aquaponic systems that are not adequately supplied with clarifiers or settlers to remove fish wastes.

 

Appendix 5 – Making homemade fish feed 

 

Fish feed is one of the most expensive inputs for a small-scale aquaponic unit. Feed is also one of the most important components of the whole aquaponic ecosystem because it sustains both the fish and vegetable growth. Therefore, it is necessary that farmers and practitioners understand its composition. Also, if commercial pelleted feed is not available, it is important to understand the methods to produce it on the farm. Moreover, homemade feed is useful when specific diets are needed to improve fish growth or aquaponic system performance.

 

COMPOSITION OF FEED 

 

Fish feed consists of all the nutrients that are required for growth, energy and reproduction. Dietary requirements are identified for proteins, amino acids, carbohydrates, lipids, energy, minerals and vitamins (Table A5.1). A brief summary of major feed components, compositional tables and formulations is presented as a guide for the feed preparation process.

 

Proteins 

 

Dietary proteins play a fundamental role for the growth and metabolism of animals. They are made of 20 different amino acids, reassembled in innumerable combinations to provide all the indispensable proteins for life and growth. Only some amino acids can be synthesized by animals while others cannot; these must be supplied in the diet. For aquatic animals, there are 10 essential amino acids (EAAs): arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. Therefore, feed formulation must find an optimal balance of EAAs to meet the specific requirements of each fish species. Non-compliance with this requirement would prevent fish from synthesizing their own proteins, and also waste the amino acids that are present. The ideal feed formulation should thus take into account the EAA levels of each ingredient and match the quantities required by fish. Information on the level of EAAs (especially methionine, cysteine and lysine) is available in any feed ingredients datasheet (see Further Reading). Recommended protein intake of fish depends on the species and age. While for tilapia and herbivorous fish the optimal ranges are 28–35 percent, carnivorous species require 38–45 percent. Juvenile fish require higher-protein diets than adults owing to their intense body growth. Besides any optimal amino acid content in the feed, it is worth stating the importance of an optimal dietary balance between proteins and energy (supplied by carbohydrates and lipids) to obtain the best growth performance and reduce costs and wastes from using proteins for energy. Although proteins can be used as a source of energy, they are much more expensive than carbohydrates and lipids, which are preferred. In aquaponics, any increase in dietary proteins directly affects the amount of nitrogen in the water. This should be balanced either by an increase in plants grown in the system or the selection of vegetables with higher nitrogen demands. In general, the total amount of crude protein (CP) or a specific EAA from a formulated feed can be simply obtained by multiplying the CP (or the percentage of the specific EAA being investigated) of each ingredient by the percentage of its inclusion, and by finally summing all the subtotals obtained. For example, a diet with 60 percent of soybean with 44 percent CP and 40 percent of wheat grain with 18.8 percent CP would be equal to → (0.6 × 44) + (0.4 × 18.8) = 26.4 + 7.52 = 33.9 percent CP. If the CP obtained by the calculation (or the amount of the specific EAA) meets the CP requirements of the fish (or the specific EAA percent) the diet is considered optimal. The identification of the cheapest protein sources can be made by simply dividing the cost of each ingredient by the percentage of its crude protein. The results will give the cost of a unit of protein (1 percent) and can help find the most cost-effective feed formula.

 

Carbohydrates 

 

Carbohydrates are the most important and cheapest energy source for animals. They are mainly composed of simple sugars and starch, while other complex structures such as cellulose and hemicellulose are not digestible by fish. In general, the maximum tolerated amount of carbohydrates should be included in the diet in order to lower the feed costs. Omnivorous and warm-water fish can easily digest quantities up to 40 percent, but the percentage falls to about 25 percent in carnivorous and cold-water fish. Carbohydrates are also used as a binding agent to ensure the feed pellet keeps its structure in water. In general, one of the most used products in extruded or pelleted feed is starch (from potato, corn, cassava or gluten wheat), which undergoes a gelatinization process at 60–85 °C that prevents pellets from easily dissolving in water. 

 

Lipids 

 

Lipids provide energy and essential fatty acids (EFAs) indispensable for the growth and other biological functions of fish. Fats also play the important role in absorbing fat-soluble vitamins and securing the production of hormones. Fish, as other animals, cannot synthesize EFAs, which have to be supplied with the diet according to the species’ needs. Deficiency in the supplement of fatty acids results in reduced growth and limited reproductive efficiency. In general, freshwater fish require a combination of both omega-3 and omega-6 fatty acids, whereas marine fish need mainly omega-3. Tilapias mostly require omega-6 in order to secure optimal growth and high feed conversion efficiency. Most diets are comprised of 5–10  percent lipids, although this percentage can be higher for some marine species. Lipid inclusion in the feed needs to follow optimal protein/energy ratios to secure good growth, to avoid misuse of protein for energy purposes (lack of fat/carbohydrates for energy purposes) and to avoid fat accumulation in the body (diet too rich in lipids).

 

Energy 

 

Energy is mainly obtained by the oxidation of carbohydrates, lipids and, to a certain extent, proteins. The energy requirements of fish are much lower than warm-blooded animals owing to the reduced needs to heat the body and to perform metabolic activities. However, each species requires an optimum amount of protein and energy to secure best growth conditions and to prevent animals from using expensive protein for energy. It is thus important that feed ingredients be carefully selected to meet the desired level of digestible energy (DE) required by each aquatic species. A brief reference on optimal protein and energy balance in most common fish for aquaponics is provided below (Table A5.1). Information on the level of DE is available in any feed ingredients datasheets (see the fish feed section in the Further Reading). In general, the value of DE from a formulated feed can be simply obtained by multiplying the DE of each ingredient by the percentage of its inclusion and by summing all the subtotals obtained (e.g. a diet with 60 percent of soybean with DE 2 888 kcal/kg and 40 percent of wheat grain with DE 2 930 kcal/kg would be equal to → [0.6 × 2 888] + [0.4 × 2 930] = 1 732 + 1 172 = 2 904 kcal/kg). If the energy obtained by the calculation meets the energy (and protein) requirements of the fish cultured, the diet is optimal.

 

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Vitamins and minerals 

 

Vitamins are organic compounds necessary to sustain growth and to perform all the physiological processes needed to support life. Vitamins must be supplied with the diet because animals do not produce them. Vitamin deficiencies are most likely to occur in intensively cultured cages and tank systems, where animals cannot rely on natural food. Degenerative syndromes are often ascribed to an insufficient supply of these vitamins and minerals. Minerals are important elements in animal life. They support skeletal growth, and are also involved in osmotic balance, energy transport, neural and endocrinal system functioning. They are the core part of many enzymes as well as blood cells. Fish require seven main minerals (calcium, phosphorus, potassium, sodium, chlorine, magnesium and sulphur) and 15  other trace minerals. These can be supplied by diet, but can also be directly absorbed from the water through the skin and gills. Supplementing of vitamins and minerals can be done according to the requirements of each species (Table A5.2).

 

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ON-FARM FEED PRODUCTION 

The production of feed requires a fine balance of all of the nutrient components mentioned above (protein, lipids, carbohydrates, vitamins, minerals and total energy). An unbalanced feed will cause reduced growth, nutritional disorders, illness and, eventually, higher production costs. Fishmeal is regarded as the best protein source for aquatic animals because of its very high protein content and it has balanced EAAs. However, it is an increasingly expensive ingredient, with concerns regarding sustainability. Moreover, fishmeal is not always available. Proteins of plant origin can adequately replace fishmeal; however, they should undergo physical (de-hulling, grinding) and thermal processes to improve their digestibility. Plant ingredients are, in fact, high in antinutritional factors that interfere with the digestion and the assimilation of nutrients by the animals, which eventually results in poor fish growth and performance. The size of the pellets should be about 20–30 percent of the fish’s mouth in order to facilitate ingestion and avoid any loss. If the pellets are too small, fish exert more energy to consume them; if too large, the fish will be unable to eat. A recommended pellet size for fish below 50 g is 2 mm, while 4 mm is ideal for pre-adults of more than 50 g. The use of any raw ingredient of animal origin (fish offal, blood meal, insects, etc.) should be preventively heat treated to prevent any microbial contamination of the aquaponic system. 

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HOMEMADE FISH FEED FORMULATIONS FOR OMNIVOROUS/HERBIVOROUS FISH 

 

Two simple recipes for a balanced fish feed containing 30 percent of CP are provided below. The first formulation is made with proteins of vegetable origin, mainly soybean meal. The second formulation is mainly made with fishmeal. The lists of the ingredients for each diet are expressed in weight (kilograms), enough to make 10 kg of feed, in Tables A5.3 and A5.4. A simple step-by-step guide on preparation of the pelleted feed is then provided. Extensive information on feed, nutrition and formulation can be found on the FAO website listed in the section on Further Reading of the publication.

 

Step-by-step preparation of homemade fish feed 

 

  1. Gather the utensils as outlined in Table A5.5. 2. Gather the ingredients shown in Table  A5.3 or Table  A5.4. Purchase previously dried and defatted soybean meal, corn meal and wheat flour. If these meals are unavailable, obtain whole soybeans, corn kernels, and wheat berries. These would need to be dried, de-hulled and ground. Moreover, whole soybeans need to be toasted at 120 °C for 1–2 minutes. 3. Weigh each ingredient following the quantities shown in the recipes above. 4. Add the dry ingredients (flours and meals) and mix thoroughly for 5–10 minutes until the mix becomes homogeneous. 5. Add the vitamin and mineral premix to the dry ingredients and mix thoroughly for another 5 minutes. Make sure that the vitamins and minerals are evenly distributed throughout the whole mixture. 6. Add the soybean oil and continue to mix for 3–5 minutes. 7. Add water to the mixture to obtain a soft, but not sticky, dough. 8. Steam-cook the dough to cause gelatinization. 9. Extrude the dough. First divide the dough into manageable pieces, and pass them through the meat mincer/pasta maker to obtain spaghetti-like strips. The mincer disc should be chosen according to the desired pellet size. 10. Dry the extruded dough by spreading the strips out on aluminium trays. If available, dry the feed strips in an electric oven at a temperature of 60–85 °C for 10–30 minutes to gelatinize starch. Check the strips regularly to avoid any burn. 11. Crumble the dry strips. Break or cut the feed on the tray with the fingers into smaller pieces. Try to make the pellets the same size. Avoid excessive pellet manipulation to prevent crumbling. Pellets can be sieved and separated in batches of homogeneous size with proper mesh sizes. 12. Store the feed. Place the fully-dried feed pellets into airtight plastic containers soon after they have been broken into pieces to prevent them absorbing humidity.

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STORING HOMEMADE FEED 

 

Once prepared, the best way to store fish feed is to put pellets into an airtight container soon after being dried and broken apart. Containers must be kept in a cool, dry, dark and ventilated place, away from pests. Keeping pellets at low levels of moisture (<  10  percent) prevents them becoming mouldy and developing toxic mycotoxins. Depending on the temperature, the pellets can be stored for as long as two months. Another way to keep pellets for long periods is to close them in a plastic container and store them in the fridge, though this would require electricity. Feed can be kept in this way for more than one year. Feed must be used on a “first in, first out” basis. Avoid using any feed showing signs of decay or mould, as this could be fatal for fish.

 

SUPPLEMENTARY FEEDING WITH LIVE FEEDS 

 

Fish can be advantageously supplied with supplementary feeds that are locally available. The use of fresh feed would in fact provide animals with supplementary proteins for their growth. It can also provide vitamins or minerals that might be deficient in the pellets. A wide range of live feeds is available – the choice depends on the fish cultured and local availability. However, it is very important to remember that any feed coming from external sources might bring micro-organisms or parasites if collected from outside waters (contaminated or polluted) or if from animal origin (e.g. worms from non-pasteurized animal manure). Live feeds can be produced at home level under safer standards or can be heat-treated before being given to fish. Examples of live fish feed include:  

  • Duckweed and aquatic macrophytes. Duckweed is quite rich in proteins and can be supplied raw for up to 10 percent of the daily ration. However, macrophytes are less digestible than formulated feed owing to their higher fibre content, which would also increase the amount of solids/wastes in the system.
  • Crop residues from aquaponics or other sources can be supplied to herbivorous/omnivorous fish in small amounts.
  • Earthworms are readily obtainable from green compost piles, especially in rural areas. A starve period of 1–2 days is recommended if worms come from outside sources in order to reduce the risk of introducing bacteria into the system.
  • Insect larvae are very rich in proteins, but care should be taken not to use them in excessive quantities owing to their higher lipid content. Larvae can be cultured on rotten organic matter (vegetables, fruits); however, a starve period of 1–2 days is recommended if the substrate contains material of animal origin.
  • Insects can be given to omnivorous or carnivorous fish species, but the presence of the exoskeleton of chitin reduces their digestibility.
  • Small fish, crustaceans and molluscs are available from streams or ponds. However, prudence may be needed owing to the risks of contamination and parasites.
  • Algae can easily be supplied to herbivorous/omnivorous fish. Algae can be cultivated in separate tanks beside the aquaponic system and harvested.

Appendix 6 – Key considerations before setting up an iAVs

 

There are many fully functioning commercial and small-scale iAVs units around the world. They can be developed not only in tropical and subtropical regions, where favourable climatic conditions allow year-round production, but also in cooler areas of the world where winter seasons last up to six months. It is especially suitable for arid climates. REWRITE?

 

The question of running an iAVs in a specific place requires a comprehensive cost–benefit analysis that should assess its possible success upon certain economic, environmental, logistical/managerial and social conditions. Many factors must be considered before embarking on a project, whether it is for domestic production or more commercially focused. 

 

Many start-up businesses fail. A decision to create a commercial enterprise requires significant research, a business plan and a risk analysis. Such aspects are beyond the scope of this appendix. However, it does discuss below some of the key factors and requirements for operating any size iAVs.

 

ECONOMIC FACTORS 

 

One of the main factors that determine the possible success of iAVsis its competitiveness against alternative production methods. 

 

The combination of both fish and plants doubles the risks of the investment that, in order to be profitable, must maximize both plant and fish production and revenues. REWRITE THIS TO FOCUS ON THE PLANTS AS MAIN INCOME?

 

 This implies that an analysis of the potential markets is an essential step towards the development of a business plan, as it should realistically find all the possible products, identify the profit margins and identify the key customers. 

 

A common mistake is to ask: “What can I produce?” instead of the more important questions: “What can I sell?”, “To whom am I going to sell?”, and only then “How am I going to produce it?” 

 

Market analysis should identify the most profitable products and the most cost effective management. 

 

This implies that the specific choice of fish can be significantly different from the species generally used in aquaponics, mainly owing to market demand and the costs of production. REWRITE

 

 In the decision-making process, there are substantial differences between a production focused for self-consumption and a market-oriented one. While the former can mostly rely on retail prices to estimate the profit margins, the commercial-scale ventures have to find markets that might be closer to wholesale prices, especially in the case of large scale operations. 

 

However, small-scale systems cannot benefit from economies of scale (e.g. a small greenhouse has a higher cost per square metre than does a larger one), which means non-commercial farmers may face higher production costs. CHECK THIS AS IAVS IS, TECHNICALLY, SCALE-ABLE, ALTHOUGH IT DOES MAKE SENSE, NEEDS TO BE REWRITTEN

 

While aquaponics may, to some extent, be acknowledged as an “organic” production option in North America, this is not equally true in Europe where “organic” still applies only to soil-based production. The positive outlook derived from a more ecologically sound production can favour higher revenues in Western markets; however, this may not be equally possible in developing countries where customers’ choices are still primarily price-oriented.REMOVE THIS AND REWRITE IT AS A SECTION ABOUT ORGANIC FOOD AND NUTRIENT DENSITY 

 

On the marketing side, an advantage could come from footprint labelling, as iAVs is the best aquaculture system in terms of water conservation and a pollution-free solution that can support agriculture with consistent savings in fertilizers and chemical inputs.

 

 However, proper product development on this basis still needs to be done, providing also that aquaponics moves towards more energy-neutral management strategies. One of the limits that still prevents aquaponics from fully expanding worldwide is that its investment costs are almost double those of standard hydroponic farming. However, this conviction is partly derived from the mistaken idea that aquaponics is a mere plant production system rather a recirculating aquaculture system (RAS) that additionally supports agriculture. If compared against a standard RAS, aquaponics shows consistent advantages in terms of capital and operating costs and for the degree of simplicity of the system. Greater success could be achieved if cost-saving designs/ projects were able to bring aquaponic setups closer to the investments costs of hydroponics. However, this would require more effort to focus on developing simpler systems. The possibility to set up aquaponics in unfavourable climates depends on the degree of investments needed for building greenhouses and running advanced climate control systems to maintain optimal water and air temperatures, humidity and ventilation. This would increase the initial and running costs, but at least, on this level, the investment costs for the greenhouse facilities may not differ significantly from those for hydroponics. REWRITE ALL THIS SO IT IS BASICALLY THE OPPOSITE!

 

ENVIRONMENTAL FACTORS 

 

There are some key considerations in determining where iAVs is most applicable and beneficial. Regions in the world where soil fertility is poor (and particularly where replenishing the soil with nutrients via organic material is difficult and/or expensive) and water is scarce are the ideal locations. 

 

iAVs is competitive with even the most productive traditional aquaculture and agriculture systems in terms of water use. iAVs food production is extremely water efficient, as the vegetable growing methods are soil-less. 

 

However, to compete against hydroponics, fish–plant systems should be considered as a whole in order to justify higher installation costs. NEED TO CHECK THIS

 

When taking these factors into consideration, semi-arid regions with poor access to water would stand to benefit the most from this new method of food production. Water is a significant factor, especially for quality standards. iAVs has the great advantage of recirculating water, which avoids any need to procure large daily volumes to compensate for losses. In areas where water is muddy, contaminated by pollutants or pathogens/parasites, iAVs, as well as RAS, is an ideal system to optimize fish production, reduce mortality of aquatic animals and improve quality. 

 

In this case, the extra investments needed to supply small volumes of good-quality water (e.g. through rain harvest or artesian wells) can be easily recovered by the added value from higher-quality fish and lower mortality rates. Salinity levels in water are the next step in the water assessment process. While freshwater fish can tolerate certain levels of salinity, increases in water electric conductivity (EC) above a certain levels (e.g. 2 000 microSiemens) limits the growth of salt-intolerant vegetables. This would push agricultural producers to consider just salt-tolerant species, with potential risks of reduced profits owing to market conditions which may not be so receptive. 

 

In addition, the buildup of nutrients and salinity through the seasons as a result of imbalances between system intake (feed) and plant uptake could equally bring the aquaponic units to face increased salinity problems. These would need to be solved through moderate water dumping or modified management (limitation in feed use, cropping with salt-absorbing plants) that might reduce systems’ profitability or productivity and may require a higher level of expertise in operators. SHOULD SALINE WATER EVEN BE MENTIONED?!

 

Climate is another major factor, as it will determine the extra cost for each unit to maintain the ideal environmental conditions for iAVs food production. In general, regions where the average daily air temperatures throughout the year are 20–30 °C are the ideal for tropical fish, such as tilapia, and warmth-tolerant plants. Therefore, the choices of crops and fish significantly affect the costs if climatic control is needed to match the ideal growing conditions of both components. 

 

Moreover, regions where average daily air temperatures are favourable, but widely fluctuate during the day and night (i.e. highlands and mountainous regions), would be particularly problematic for fish production. This is because large changes cause stress to the animals. Attention must also be paid to the seasons. Cold winter seasons will force iAVs farmers to either invest in energy-demanding heating systems for their greenhouses or stop production entirely for certain months. It is thus important to study the production setup carefully and possibly find alternative species that avoid unproductive sections of the year. 

 

Extended rainy seasons force farmers to protect their units with strong canopies or greenhouses, as large volumes of rain could damage crops or cause the systems to overflow or to dilute excessively the nutrients in water. However, if on the one hand this need requires extra investments, on the other it can be profitable in areas where traditional agriculture is severely limited owing to flooding or nutrient runoff. The same solution also pertains to wind, as the presence of a protected environment could bring higher yields and better quality of vegetable products, while traditional agriculture would struggle. 

 

Summer seasons can cause water overheating. Although methods to keep temperatures relatively low during hot periods are quite simple and can be supported with proper system designs, it is possible that water temperatures would rise to suboptimal levels during extremely hot periods if no water cooling systems were used. This would limit farmers’ vegetable growth and selection, even though it may not affect tropical fish or nitrifying bacteria. 

 

LOGISTICAL AND MANAGERIAL FACTORS 

 

Fish production is an important component of iAVs operations. Easy access to aquatic animals is fundamental for farmers, as is the possibility to gain expertise on fish and knowledge of locally cultured fish. 

iAVs expansion may limited in regions where there are no hatcheries, aquaculture production or extension services – unless broodstock, fingerling and fish feed productions are all part of the iAVs business plan. 

 

Even then, the investment appears riskier, as it implies longer periods to make the farm fully operative, and the need to dedicate more time for knowledge transfer and to scope potential local and regional markets where to sell the production. REMOVE THIS?

 

At any location, access to electricity and appropriate water is essential. Particularly for electricity, the access to a constant and reliable power-grid is fundamental to secure the continuous functioning of pumps. The lack of this resource would severely limit the expansion of aquaponics unless low-yielding systems are designed to withstand power cuts of several hours without affecting fish survival. REWRITE THIS AS IAVS CAN BE ADAPTED TO LOCATIONS WITHOUT ELECTRICITY

 

iAVs operations meant for commercial purposes, must rely on backup systems and generators, which increase the setup costs. 

 

Fish production is one of the most complicated aspects of iAVs IS IT???(particularly for farmers new to aquaculture), demanding daily management and care to avoid significant losses if any system failure occurs. There must also be a market for key iAVs components and monitoring tools (water test kits, pH meters), which a local aquaculture market would normally facilitate. 

 

A determinant factor for the success of any iAVs is the use of locally available materials and the sensible adaptation of systems to local contexts and resources. 

 

Educational capacity is also a key factor when selecting specific locations within regions or countries. iAVs requires an understanding of this integrated ecosystem as well as the major factors that influence it (water, environment, nutrition, etc.). It also demands good individual aquaculture and horticulture knowledge that must be transferred and adapted to local contexts. 

 

The major benefit of iAVs is that illiterate or semi-illiterate farmers and/or end users can adapt the technology, or at least the concept, to local resources, needs and cultures. Adapting and contextualizing the systems would bring them closer to those fish/plant systems that have dominated agricultural practices for thousands of years. This would require a better knowledge among practitioners on how to design systems where every single component or material could reduce management needs to a minimum. Where aquaponic food production is virtually non-existent within a specific region, it is beneficial to partner with local universities or agricultural extension institutes in order to develop knowledge on best practices and on how to develop aquaponics in a very simple and effective way. REWRITE OR REMOVE

 

SOCIAL CONDITIONS 

 

Beyond the adoption of fish–plant systems as a competitive food production method, iAVshas still not acquired a well-defined outlook. While aquaponics is widely accepted as an organic production method in North America, the same cannot be seen in Europe and this reduces its potential to gain premium prices. Among consumers and researchers, there are also some concerns that aquaponic water is a vector of potential bacteria contaminations owing to fish faecal wastes. Although different countries use different regulations on water safety, the development of aquaponics may be limited in those countries where the limit for bacteria is more stringent. This would require an increase in efforts to comply with local standards (e.g. by using sterilizing technology), even though aquaculture wastewater is safer than other water sources. On the other hand, aquaponics can provide an opportunity to produce safer food that is chemical-free and disease-free. In the case of the aquaculture industry, this may be an added-value characteristic that may raise interest in this production system. Recent concerns about pesticide use in agriculture have led many consumers in developing countries to buy safer products. These consumption patterns must be accurately monitored in the decision-making process as to whether aquaponics is feasible in a particular area or not. REWRITE WITH INFO ABOUT ORGANIC CERTIFICATION ADDED

 

SUMMARY OF ESSENTIAL REQUIREMENTS FOR iAVs AT DIFFERENT SCALES 

 

Table  A6.1 summarizes the key considerations for iAVs ventures on various scales.

 

TABLE SKIPPED – replace with a new one?

 

Appendix 7 – Cost-benefit analysis for small-scale iAVs  

 

Tables A7.1–A7.4 describe the costs and benefits of a small-scale aquaponic unit. 

 

The information in the tables is meant to provide the reader an understanding of the expenses necessary to build and run an iAVs, as well as the expected production and incomes in the first year. 

 

Table  A7.1 summarizes the total cost of materials for the initial installation (capital investment) for a small-scale media bed unit (the full list of materials and costs for this unit can be found in Appendix 8 of this publication). Table  A7.2 details all the yearly running costs involved. The details of the running cost calculations can be found in the notes section of the table. Table A7.3 details the expected production of vegetables and fish in one year. Table A7.4 brings together the costs and revenues from Tables A7.1–A7.3 and shows the total profit on the initial investment and the payback period. It should be noted that the figures given in the tables are only intended as guidelines for new users. It is difficult to provide accurate figures, particularly regarding production yields and their values, as many production and financial factors may influence them: temperatures, seasons, fish type, fish feed quality and percentage protein, markets prices, etc.TOTAL REWRITE TO MATCH IAVS COSTS

CALCULATION ASSUMPTIONS

 

  • All calculations are based on a small-scale media bed unit (described throughout the main text of this publication) with 3 m2 of growing space and 1 000 litres of fish tank space (as shown in Appendix 8 of this publication).
  • The unit is meant for domestic food consumption only and not for small-scale income-generating production. The financial benefits can vary and might be larger than the figures shown in Table A7.4 if farmers select more profitable crops to grow. As the focus is on small-scale  iAVs for domestic food consumption, two crops have been considered in the calculations as these better reflect the production patterns of users growing food for consumption only: one leafy green (lettuce) and one fruiting vegetable (tomato). REPLACE THE LETTUCE WITH A MORE NUTRITOUS PLANT?
  • Yield data are obtained from a continuous production of 12 months, feeding the fish with good-quality 32 percent protein feed daily in unit water temperatures of 23–26 °C throughout the year.
  • The units have a constant standing fish biomass of 10–20 kg. CHECK
  • The fish cultured are tilapias. They are fed on a feeding ratio of 50 g per square metre of growing space, equivalent to a total feed consumption of 150 g per day (50 g × 3 m2). The stocking weight of juvenile fish is 50 g; the expected harvest weight is 500 g per fish in 6–8 months.
  • The average yields for amateur growers have been considered in the calculations: 20 heads of lettuce per square metre per month, and 3 kg of tomatoes per square metre per month.

 

SKIPPED 3 TABLES AND NOTES

 

Important: 

 

The calculations are based on a staggered production of fish in an established aquaponic system. The expected production is lower from a newly established system stocked only with juvenile fish of the same age. For new systems, it is thus suggested that fingerlings be stocked in greater numbers in order to supply enough nutrients to plants. In this case, harvesting of the first fish can start from the third or fourth month onward (with fish at 150–250 g) in order to maintain a steady biomass

 

TABLE SKIPPED

 

Taking the final figures from yearly operating costs and yearly revenues (Tables A7.2 and A7.3), the total profit is USD441 (Table A7.4). This suggests that in general, once a unit is set up, USD1.38 net profit is earned for every USD1 invested in growing food using a small-scale aquaponics unit for domestic consumption. The payback period for the initial investment is 19 months. Reducing the capital costs (e.g. using recycled tanks) or running costs (e.g. supplementing fish feed), or increasing the revenue (e.g. specialty markets), will considerably decrease the payback period. 

 

Appendix 8 – Step-by-step guide to constructing small-scale aquaponic systems

 

This step-by-step guide describes how to build the media bed, nutrient film technique (NFT) and deep water culture (DWC) systems for the small-scale aquaponic units described in Chapter 4 of this publication.

 

INITIAL COMMENTS ON THE THREE SYSTEM DESIGNS 

 

The actual design theory for the three systems is explained in Chapter  4 of this publication. This appendix focuses solely on how to construct them using cheap materials that are widely available. In addition, it provides brief explanatory comments for some of the most complicated components of each system. The key factors considered for the design of each unit are: i) material cost; ii) material availability; and iii) production capacity. Thus, the materials for each design shown in the diagrams have all been selected because they are all widely accessible. The main material used for fish tanks, media beds and DWC canals is the intermediate bulk container (IBC). This is a container with a capacity of about 1  000  litres used to transport different liquids worldwide. However, for all components of each unit design, local/cheaper materials can be substituted, but the recommendations for alternative materials stated in Chapter 4 of this publication should be followed. There are three major sections to the appendix. The first section shows how to build the media bed unit using fabricated IBC containers for the fish tank, media beds and sump tank. The second section describes how to build an NFT unit. This includes how to set up the fish tank (same as the media bed unit), how to make and install a mechanical separator and a biofilter using polyethylene barrel containers and how to install the NFT grow pipes using standard 4 inch (110 cm) PVC drainage pipe. The third and final section shows how to build the DWC unit. The same fish tank design is employed along with the same swirl clarifier and biofilter described for the NFT unit. The other parts show how to set up the DWC canals and prepare rafts using polystyrene sheets. An index of all materials and tools used for each section is given in the following pages which should be referred to for each of the major unit construction sections

SKIPPED – TABLE OF CONTENTS (Appendix 8)

 

SECTION 1 – THE MEDIA BED UNIT

 

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1. PREPARING THE FISH TANK

 

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  1. INSTALLING THE FISH TANK EXIT PIPE
  2. PREPARING THE MEDIA BEDS AND SUMP TANK
  3. MAKING TWO MEDIA BEDS FROM ONE IBC
  4. METAL SUPPORTS FOR BOTH MEDIA BEDS
  5. MAKING A SUMP TANK AND ONE MEDIA BED FROM AN IBC
  6. ASSEMBLING THE MEDIA BEDS AND SUMP TANK
  7. PLUMBING THE UNIT: FISH TANK TO THE MEDIA BEDS (DISTRIBUTION MANIFOLD)
  8. PLUMBING THE UNIT: MEDIA BEDS TO THE SUMP TANK (DRAIN PIPE)
  9. PLUMBING THE UNIT: SUMP TANK TO THE FISH TANK
  10. ADDING THE MEDIUM AND RUNNING THE UNIT

 

SECTION 2 – Building the iAVs in Developing Nations

iAVs had its roots in a quest to develop a new method of agriculture for arid-zone underdeveloped regions such as the African Sahel.

While the following images depict the development of such a low-cost, low-tech iAVs, a similar system can meet the needs of a family of four for fresh fish and nutritious vegetables……in a space no larger than a parking spot at your local supermarket.

Proportions depicted are approximate and the materials and configuration can be varied to suit the resources and skills of the user.

In its simplest form, an iAVs comprises a grow bed containing medium-coarse sand (which functions as the bio-filter and plant substrate) which drains into a fish tank.

The grow bed and fish tank can be made watertight with puddled clay, plastic liner or fibreglass.

Furrows are formed in the sand and seedlings are planted into the high sections of the furrows.

Nutrient-rich water is intermittently transferred from the fish tank into the furrows.

As the water percolates down through the sand, the fish solids are trapped and mineralised and become nutrients for the plants.  The clean water drains back to the fish tank.

This symbiotic partnership will see the water recycled up to 300 times before it is used up by the plants.

The reddish tint in the image represents a liner of expansive clay (where available) as an alternative to synthetic membrane for water retention.  The weir could be woven stick and thatch,  or brick/rock wall, scrap tin, logs & mud, boards……whatever is available.  Many alternative configurations…..both low/hi-tech are possible.

 

The image above shows a pipe or hose to move water to the far end of the bio-filter This is not actually necessary.  Return (drainage) with cascade aeration is not clearly depicted.

 

The example above illustrates water transfer by means of a mechanical hand-operated pump.

Could also employ solar-PV, a shadoof, animal-powered pump, windmill or even a simple calabash (bucket on a rope/stick).

The iAVs provides for 100-fold greater water use efficiency over traditional pond culture of tilapia with (the nutritionally and economically dominant) vegetable production for the same amount of water that it would take just to grow the fish.

Total annual water consumption is as low as 5 cubic metres/year for each cubic metre of fish culture volume – with a significant fraction of that water use in the form of edible biomass.

-o0o-

Credits:  Pastel renderings by Brandy Noon, a Kenyan, circa 1992.  Captions by Mark R. McMurtry.

 

SECTION 3 – THE DEEP WATER CULTURE (DWC) UNIT

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APPENDIX 9

NEED TO MOVE SOME OF THE OTHER SECTIONS INTO THIS ONE – SHOULD THIS BE MADE INTO IT’S OWN SECTION IN THE BOOK ITSELF

 

Commercial Production

Commercial production in the context of Integrated AquaVegeculture Systems (iAVs) or Sandponics is not merely about achieving high volumes. It requires a comprehensive understanding of both the production and marketing aspects of the business.

Production

The production aspect, while seemingly straightforward, requires a certain level of expertise. It assumes the presence of competent skill-sets, adequate capital, commitment, experience, and contingency planning. Large scale growers often grow their products under contract, meaning the product is pre-sold at an assured volume, quality, timeframe, and price. This approach is common in various sectors, from bedding plants and cut flowers to high-performance vegetables and virtually all field vegetable crops in the US5.

Marketing

On the other hand, marketing perishable commodities at volume is a complex task that requires a deep understanding of the established channels for both fish and produce. It is not a game for amateurs. Selling and growing are vastly distinct enterprises requiring different skill sets. To be profitable, both skills need to be present in abundance.

The Interplay of Production and Marketing

Successful commercialization requires far more than merely achieving production at volume. Crop selection and production methodology have little to do with selling volume at a profit reliably. Growing and marketing are vast disparate endeavors, and neither should be attempted by novices in a commercial context.

The Role of Experience and Enthusiasm

Experience plays a crucial role in commercial production. What may appear grossly obvious to experienced professionals may not be to some. Enthusiasm can often function as a ‘mask’ for naivety. Many well-intentioned, even gifted, growers have gone bankrupt by diving into the deep-end without a viable flotation device.

The Importance of Understanding Strengths and Weaknesses

Understanding one’s strengths and weaknesses is crucial in commercial production. No one individual has all the skills required to commercialize iAVs or anything else. It is important to recognize where one’s strengths and weaknesses lie. Many, unfortunately, do not.

 

Aquaponics quick-reference handout

 

Note: The section below reproduces the chapter summaries from the FAO aquaponic publication (see citation below). It is intended to be a short and easy-to-reproduce supplement, envisioned for use in education, extension and outreach applications and is designed to be provided to students, workers and farmers. The full technical paper can be found at: www.fao.org/publications/en/ Somerville, C., Cohen, M., Pantanella, E., Stankus, A. & Lovatelli, A. 2014. Small-scale aquaponic food production. Integrated fish and plant farming. FAO Fisheries and Aquaculture Technical Paper. No. 589. Rome, FAO. 262 pp. 

 

INTRODUCTION TO AQUAPONICS 

 

Aquaponics is the integration of recirculating aquaculture system (RAS) and hydroponics in one production system. In an aquaponic unit, water from the fish tank cycles through filters, plant grow beds and then back to the fish. In the filters the water is cleaned from the fish wastes by a mechanical filter that removes the solid part, and a biofilter that processes the dissolved wastes. The biofilter provides a location for bacteria to convert ammonia, which is toxic for fish, into nitrate, a more accessible nutrient for plants. This process is called nitrification. As the water (containing nitrate and other nutrients) travels through plant grow beds the plants uptake these nutrients, and finally the water returns to the fish tank purified. This process allows the fish, plants, and bacteria to thrive symbiotically and to work together to create a healthy growing environment for each other, provided that the system is properly balanced. Although the production of fish and vegetables is the most visible output of aquaponic units, it is essential to understand that aquaponics is the management of a complete ecosystem that includes three major groups of organisms: fish, plants and bacteria. In aquaponics, the aquaculture effluent is diverted through plant beds and not released to the environment, while at the same time the nutrients for the plants are supplied from a sustainable, cost-effective and non-chemical source. This integration removes some of the unsustainable factors of running aquaculture and hydroponic systems independently. Beyond the benefits derived by this integration, aquaponics has shown that its plant and fish productions are comparable with hydroponics and RASs. Aquaponics can be much more productive and economically feasible in certain situations, especially where land and water are limited. However, aquaponics is complicated and requires substantial start-up costs. The increased production must compensate for the higher investment costs needed to integrate the two systems. Before committing to a large or expensive system, a full business plan considering economic, environmental, social and logistical aspects should be conducted.

 

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BENEFITS AND WEAKNESSES OF AQUAPONIC FOOD PRODUCTION 

Major benefits of aquaponic food production:

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Major weaknesses of aquaponic food production:

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TECHNICAL INTRODUCTION

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WATER QUALITY IN AQUAPONICS

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AQUAPONIC UNIT DESIGN

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BACTERIA IN AQUAPONICS

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PLANTS IN AQUAPONICS

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FISH IN AQUAPONICS

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BALANCING THE FISH AND PLANTS: COMPONENT CALCULATIONS

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ADDITIONAL TOPICS IN AQUAPONICS

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TEN KEY GUIDELINES FOR SUCCESSFUL AQUAPONICS

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Aquaponics is a symbiotic integration of two mature disciplines – aquaculture and hydroponics. This technical paper discusses the three groups of living organisms (bacteria, plants and fish) that make up the aquaponic ecosystem. It presents management strategies and troubleshooting practices, as well as related topics, specifically highlighting the advantages and disadvantages of this method of food production. This publication discusses the main theoretical concepts of aquaponics, including the nitrogen cycle, the role of bacteria, and the concept of balancing an aquaponic unit. It considers water quality, testing and sourcing for aquaponics, as well as methods and theories of unit design, including the three main methods of aquaponic systems: media beds, nutrient film technique, and deep water culture. The publication includes other key topics: ideal conditions for common plants grown in aquaponics; chemical and biological controls of common pests and diseases including a compatible planting guide; common fish diseases and related symptoms, causes and remedies; tools to calculate the ammonia produced and biofiltration media required for a certain amount of fish feed; production of homemade fish food; guidelines and considerations for establishing aquaponic units; a cost–benefit analysis of a small-scale, media bed aquaponic unit; a comprehensive guide to building small-scale versions of each of the three aquaponic methods; and a brief summary of this publication designed as a supplemental handout for outreach, extension and education. Aquaponics is an integrated approach to efficient and sustainable intensification of agriculture that meets the needs of water scarcity initiatives. Globally, improved agricultural practices are needed to alleviate rural poverty and enhance food security. Aquaponics is residue-free, and avoids the use of chemical fertilizers and pesticides. Aquaponics is a labour-saving technique, and can be inclusive of many gender and age categories. In the face of population growth, climate change and dwindling supplies of water and arable land worldwide, developing efficient and integrated agriculture techniques will support economic development.