Module 6 – Fish

Fish

If you’ve never kept fish before, you may be faintly hesitant at the prospect.

Relax!

When you operate authentic iAVs, you are engaging in freshwater aquaculture in its simplest and most cost-effective way.

Freshwater aquaculture has been the subject of many doctorates…and its experts have published many substantial books.

My point is that in a short course like this, we won’t be teaching anything much about aquaculture.

We’ll help you to broaden your aquaculture knowledge and skills over time but, for now, we’ll be focused on showing you how to keep fish the iAVs way.

We’ll provide close direction so that you can grow as you learn…and learn as you grow!

iAVs-Suitable Fish

While there are many species that will grow in an iAVs, the fish that we prefer are robust, fast-growing and always ready to eat.

We want them to eat plenty of food – so that they grow quickly and produce copious quantities of waste – to be converted to plant-available nutrients – to enable us to grow more plants.

If you are someplace where tilapia are available – and you can lawfully keep them – then I’m happy to suggest that they be your initial choice – particularly if you can get all-male hybrid tilapia. They grow quickly and are almost bulletproof.

A glimpse at just some of the fish that can be raised in an iAVs Sandgarden.

The Aquatic Environment

Water temperature

Freshwater fish species are distinguished by their requirement for a specific water temperature range – loosely described as warm water and cold water. All of those in the list above are warm water species and they thrive in a temperature range of 25^oC to 32^oC.

In Southeast Asian countries, Anabas testudineus (the climbing gourami) may be a useful alternative to tilapia.  African catfish and Indian catfish are, like tilapia, robust fish and they are widely used as food fish in the areas from which they take their names.

If you live in Australia, you are not legally able to keep tilapia, so I’d suggest jade perch as an alternative.

Then we have the cold-water species.  The most commonly available cold-water species is the trout…particularly the rainbow and brown varieties.  They do best in a temperature range of 12^oC to 17^oC

The temperature ranges that we’ve proposed are those at which, all other things being equal, the fish will thrive.  The further we get away from that temperature range, the more likely we are to encounter problems.

Exceeding the temperature range will stress the fish and impact their ability to eat.

Fish that are not eating are not creating the same quantity of waste so the plants are no longer receiving the required amount of nutrients.

As temperatures continue to rise or fall (depending on the species) they reach the sub-lethal stage – beyond which the fish will die.

Outside of the tropics (where day/night average temperatures are closer than in cooler zones), you may need to consider heating/cooling your fish tanks to maintain them within the optimal range. This can be a serious expense if you are buying your electricity from a utility. Fortunately, there are lots of useful alternative (active and passive) heating options.

Another distinction between warm-water species and cold-water ones is their requirement for oxygen.  Warm water contains less ‘dissolved’ oxygen than cold water.  Warmwater fish need less oxygen.  Cold-water species need more oxygen.

The lack of dissolved oxygen will kill fish very quickly – so it’s time we had a chat about aeration.

Dissolved Oxygen

Oxygenation occurs naturally at the point that air and water make contact – at the surface of the water.

Whenever the water is disturbed…its surface expands and the capacity to take up oxygen is increased.  That happens in our IAVs sandgarden whenever the timer triggers an irrigation event.  The water that drains back into the fish tank breaks the surface and expands it…and all that ‘new’ surface gets recharged with oxygen.

While not essential in every instance, supplementary aeration is cheap insurance against the impact of low dissolved oxygen levels – particularly during the night when there are no irrigation events.

Air Pumps

Growing Season

Your fish growing season depends on how long you can cost-effectively maintain the water temperature – and dissolved oxygen levels – within the recommended range for the species you have chosen.

You are fortunate if you live where the year-round water temperature falls within the range of your preferred species.

For those of us who live everywhere else, life is a little more complicated.

Once you’ve made a decision about the fish species you plan to keep, you need to decide on numbers.

How Many?

Mark McMurtry’s research demonstrated that 80 fingerlings (15g each) per 1000 litres of water – fed to satiation – would provide sufficient nutrients for 4 tomato plants – each producing 4 – 5kg of fruit in a 100-day cycle.

That means 80 fingerlings are required for the Starter IAVs. A square metre iAVs will require around 15 fish and A Carpark iAVs will accommodate 250 fish.

Having decided on the number of fish that you will keep, you place an order.

Sourcing Fish

You can order fingerlings from:

• Fish hatcheries
• Aquarium supply stores
• Fish restocking programs
• Other specialist breeders

Fish hatcheries may have a minimum order – quite often it’s 100 fingerlings but they will be the cheapest fish you’ll buy. Aquarium shops may be able to handle the smaller numbers you need but they will be much more expensive – and more likely to have an infestation or disease of some type. Fish restocking programs may be able to help you depending on the species required.

Acclimating the Fish

The multi-stage process that enables fish to live in a recirculating system like iAVs is known as the aquatic nitrogen cycle.

Simply put, the fish produce waste which quickly generates ammonia.

One class of naturally occurring bacteria… convert ammonia into ammonium nitrite.  Another class of useful bacteria convert the nitrite into plant-available ammonium nitrate. In fact, it’s all a bit more complicated than that but it’s all we need for now.

While it will establish itself over time, the quickest way to get the nitrogen cycle happening in your sandgarden is to obtain a bottle of Fritzsyme “7 from your local aquarium supply store.

https://fritzaquatics.com/products/fritzzyme-7-freshwater

While it’s not essential, it will lower the risk threshold for the fish during the first few days.

We’ll add that to the water a day to two before we add the fish.

Acclimating the fingerlings is not just about the aquatic nitrogen cycle. We also need to ensure that the pH and water temperature of the water containing the fish – and that in the fish tank – equalise. Temperature and pH shocks are to be avoided.

Introducing the Fingerlings

If your fingerlings are from a hatchery, they will arrive in an oxygen-filled plastic bag inside a carton or Styrofoam box.

Cut a small slit in the plastic bag and float it on the water surface in the fish tank to allow the temperature of the water and the pH in the fish tank – and the bag – to equalise. The process of adding fingerlings to your system will take about 30 minutes by the time everything has normalised and the fish will be swimming in their new home.

Fish Feeding

This topic alone could easily be several long chapters in a book – or an entire book in itself – which we won’t be writing.  Ever!

We strongly recommend that you study the requirements, behaviours and life-cycle factors of the species you are attempting to grow – from responsible sources in your area.

In the meantime, however, we’ll be taking the following proven iAVs approach:

Feed times

• 6:00 am (dawn or pre-dawn) – 1st pump cycle of the day starts)
• 6:30 am – drainage completed.  Feed fish all they’ll eat in 15 minutes
• 8:00 am – 2nd pump cycle (1/4 of tank volume, each)
• 10:00 am – 3rd pump cycle
• 12:00 pm – 4th pump cycle
• 1:45 pm – Feed fish all they’ll eat in 15 minutes
• 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).

At the prescribed times – and without disturbing the fish too much – sprinkle feed across the water surface.

Continue to add more feed for as long as the fish are eating it – or for a maximum of fifteen minutes.   Our goal is to get them to eat as much as they need – without wasting the feed.

All other things being equal, you can continue to do this – twice a day – thereafter.

This is the easy way so we’re going to go with that for the moment.

The important thing to remember is that good feed in the right quantities promotes rapid growth of fish – and that means early harvests.

Harvesting

Fish can be harvested at any stage of their growth.  It all comes down to what you plan to do with them.

For practical purposes, they can be incorporated into a menu at 100gm and beyond but it’s usually more viable to grow them out further.

Plate-sized fish range from 250gm to 400gm.  If you want fillets, you can grow them out to 12 months and beyond.

That’s a decision that you can make further down the track.  For now, we’ll be assuming a 100-day crop cycle.

And the mention of crop cycles brings us to the subject of plants.

Key Points

• Raising fish in an iAVs is easy.
• Feed your fish what they will eat – and reap the rewards. Scrimping on feed is false economy.
• The idea of two crops – one of fish and the other of fruit and vegetables – for the same amount of water is extremely powerful. The sheer efficiency of the water use put iAVs into a completely different water use category.
• The iAVs method has a predictable and quantifiable connection – from the amount of feed given to the fish – to the weight of fish and plant biomass produced by the system.