Interview with Donald Bailey Director of University of Virgin Islands Aquaponics Program



Hey everybody, welcome to the Growing with Fishes Podcast. I’m Steve.
And I’m Marty.
I’m Don.
And I’m Fish. This is the Growing with Fishes Podcast. We have both of our co-hosts today, and we’re also—oh, wait, hold on, feedback there. Alright, sorry about that. I always forget that that starts in the beginning. Anyway, we are joined today by Donald Bailey, who is one of the long-time experts at UVI. He’s been there pretty much since the beginning. In fact, you were there since the beginning, correct?
I missed the beginning by about five years.
Okay, but he’s definitely one of the longest-running researchers at UVI. For those of you who don’t know, they founded the commercial aquaponics model, the generally accepted commercial aquaponics model that’s out there. It is a big honor to have him on the show today. Thanks for joining us.
It’s my pleasure to be here. Thank you.

So, why don’t you tell us about how you got started at UVI and then a little bit of the history of aquaponics, and how you guys have come to be what you are today?
Well, it all started in 1979 when Jim Rakocy came to the Agriculture Experiment Station at UVI, and I joined here in 1986. The problems that Virgin Islands farmers face include a lack of arable land—good agricultural land to grow crops on—and also a kind of irregular rainfall pattern that’s pretty seasonal. There’s no good surface water, like rivers, to pull irrigation water from. The wells are pretty salty, and you can’t rely on rainfall. So, land and water issues were the problems that Dr. Rakocy was given to solve. His concept was to integrate fish production with vegetable production in a hydroponic system, and that’s the beginning of how it all developed.

The idea of aquaponics, of course, existed before that, and his research had been using water hyacinths to clean water from fish production. Moving from just water hyacinths—a plant that would get discarded—to a vegetable crop that has economic value was another key development we made here. Instead of just mitigating wastewater, we’re getting a fish crop and a vegetable crop out of the same system.

A third point was the reduction of waste discharged into the environment. If you’re just going to do a straight aquaculture system, recirculating aquaculture, you’re going to have wastewater that gets discharged, which might go into receiving streams or you might have to send it to a municipal sewage system for treatment, and that’s going to be a cost. So, if you can reduce the amount of waste that you need to discharge into the environment, that’s also a bonus.

Those are pretty much the three guiding principles behind our work: intensification of production in a small area of land, really conservative use of water, and minimal discharge into the environment. Initially, we started with media beds using gravel solids filtration from the local quarry, but found that there were a number of different problems associated with media beds. By the time I arrived here in ’86, they had already conducted their first experiment where they removed the gravel media from one set of research systems and switched to using floating Styrofoam rafts. Since ’86, we have been utilizing floating deep water culture on rafts.

Deep Water Culture and Solids Filtration
Jumping into deep water culture, regarding solids filtration, we employ passive solids removal. We have a clarifier that, by allowing sufficient residence time in the tank, lets the solids settle out of the water. However, this method is pretty inefficient. To address this, we use net tanks that trap the remaining solids using orchard netting, typically used to cover trees to protect them from birds preying on fruit. Both methods are relatively inefficient, but they are cost-effective. Our main clarifier tank costs about a thousand dollars, and the net tanks are a couple of hundred dollars each. Although there’s an upfront cost, it’s a small part of the overall system cost. However, there is ongoing labor required to keep these components clean. Removing solids from the clarifier is straightforward, but cleaning the net tanks takes about an hour each week.
There are more technologically advanced options like drum filters that can remove all the solids from a system, but they are much more expensive. We’re not as much a fan of radial flow filters or slow swirl filters as much as we are of clarifiers where the solids just settle. We’ve used slow swirl filters, and they are about as efficient as the clarifier. We published a study a few years ago comparing them, and the settling tanks performed similarly in terms of solids removal. I have not used radial flow filters.

System Size and Production
Regarding the total size of the systems we run, our largest system, which we consider our commercial-scale system, contains 30,000 gallons of water. The fish rearing tanks hold about 9,000 gallons, and the rest of the water is in the hydroponic tanks, covering 214 square meters or approximately 2,303 square feet (72 rafts that are 8 by 4 feet each).
Our production yields about 10,000 pounds of tilapia annually. During our prime lettuce season, which runs from November to March, we can produce 35 to 40 cases of lettuce each week. In warmer weather, we switch to growing cucumbers, okra, and squash, as most leafy greens decrease in production due to a mere five-degree difference in water temperatures, which significantly affects oxygenation and root development.

Research and Adjustments
We haven’t extensively tested silica in relation to aquaponics. It’s not a standard element tested by our lab, but it’s something we might explore. We currently use potassium hydroxide for pH adjustment, but we could consider using potassium silicate to enhance silica levels, which has been found beneficial for plant stress and disease prevention in various crops.

Fish Rearing and Feeding
In our fish rearing tanks, we practice staggered stocking. Every six weeks, we stock a rearing tank with 650-gram fish and allow them to grow for 24 weeks before harvesting. This schedule results in eight to nine harvests per year, depending on the calendar, with each harvest producing around 1,000 to 1,200 pounds of fish, assuming uniform growth and survival.
We feed the fish a high-quality diet of Purina Aquamax, which contains 32% protein, to ensure rapid growth. There’s interest in alternative feeds, such as duckweed, which we are currently researching. Duckweed could potentially be grown from the waste collected from the system, providing a sustainable feed alternative.

How much you can produce and whether it slows down the growth rate enough that you’re going to substitute out some of the food you’re importing and feeding the fish with duckweed. There’s going to be a trade-off, and there’ll be a break-even point that you can determine at what point it is worthwhile to grow duckweed to feed the fish.

System Walkthrough:
The solid waste is removed from the system in the clarifier and the net tanks, which we have already discussed a bit. You don’t want any of that solid waste going out into the hydroponic tanks because it clogs up the plant roots in the first section of the trough. If it does settle out at the bottom of the hydroponic troughs, it will just decay, becoming a secondary source of ammonia and another water quality factor that you have to manage. Therefore, getting all the solids out before they reach the hydroponic tanks is critical.Our hydroponic beds are four feet wide and 100 feet long, and they are paired so that the water travels down and back into the sump. When you look at pictures of our system, you see these three pairs of hydroponic tanks. That’s an artifact of how we developed our technology. We had two smaller systems for a couple of years and wanted to modify the design of the fish production side. So, we took out the rearing tanks and combined those pairs of hydroponic tanks. If I were to start from scratch, I would make just one pair of two hydroponic tanks. They’d be wider and longer but have the same growing area as what we have now, which would save on some space.The water then returns from the hydroponic tanks into the sump. We have a half-horsepower circulating pump down there, and the water gets pumped up to the rearing tank and off it goes again. It takes about five hours for the water to cycle through from the sump, through the rearing tanks and other components, and then back to the sump.

Experimentation with Black Soldier Flies:
We have grown black soldier flies, which is another good possibility. We don’t currently process any of our fish, so we didn’t have many fish carcasses to deal with. However, I like the idea of using a processing plant to feed them your fish carcasses, which is definitely a good way to get rid of them. But sourcing all that material for black soldier flies is, I think, the limiting factor. If I were to go around the island and ask for all the plate scrapings from restaurants, that becomes too costly in terms of my time and effort. So, I would really want to have that waste stream to be on-site and be able to grow my black soldier flies with something that I’m producing myself instead of sourcing it from other facilities.

Surprises and Challenges:
One big drawback of our system is actually the energy use. Because we’ve intensified the system, we’re required to aerate the fish tanks to keep all those water quality parameters at their highest level. To do all that, we use a lot of energy. So, it’s really a problem we need to address. What is the trade-off when you start reducing the amount of aeration into the tanks? Especially, I would cut air to the hydroponic trough and see how that impacts the plant growth.

Marty: Did you have a question?
Speaker: No, um, what’s up?
Marty: Oh yeah, well, I was just wondering… you were talking about energy use being a constraint, and the oxygen… Are you thinking about experimenting with it, or have you already started? I think my internet skipped out for a second. You said you were either thinking about it or had already started experimenting with cutting off your oxygen supply to the tank, is that right?
Speaker: Yep, we’re more thinking about it than doing it right now. Hopefully, we’ll be doing it by May. Last fall, since we have those three pairs of hydroponic tanks, I do have some options. I cut off all the air to one set of hydroponic troughs and reduced the air to another pair by half, and left the other pair operating normally. There were definitely differences. The system with no air at any time of the day, 24 hours off, definitely had much smaller plants. So, my idea is actually just to turn off the aeration at night, which kind of couples with going off-grid. If I’m able to reduce the amount of aeration I need overnight, then I would need less battery backup to run my system.
Marty: Have you considered maybe draining those tanks? I know maybe in your system you can’t do it right now, but one of the things that I’ve done before is shut down some of my systems for a period of time and just made sure that the tanks were empty as opposed to full, so you weren’t doing that. I don’t know if you guys have thought about doing that, but I definitely have considered that as well for myself, just in terms of power usage. Even shutting down the system altogether for certain lengths of time, or using timers as opposed to right now, I use siphon systems so that it’s constantly running and gives the roots exposure to air without pulling it from the water. But I’ve been wanting, and I haven’t done it yet, but basically combine the two where you would be able to drain the raft beds and still have the roots suspended in the dark.
Speaker: Yeah, we would definitely have to re-engineer the system to do that. I was thinking you probably have to lift it up in the air; it probably sits too low for that now. We’ve got a lot of water in those tanks and sumps, and to drain them out, you need to have a sump somewhere on the side to hold that quantity of water. That would be our constraint. And yeah, there are different ways to engineer around a problem, and that might be a solution. But if you’re in a greenhouse where you’re already constrained by space or available land, you have to think about where you’d put that water when you drain it out.
Speaker: Right now, in my system, we’re growing two kinds of lettuce, bok choy, and kale, two kinds of basil—the green Genovese and a red one called Red Rubin. I’ve got some sunflowers in right now for the cut flower business. I’ve got some tomatoes, really for the first time in a long time. I really shy away from fruiting crops. I like crops, especially leafy greens, that are in and out within a three to four-week time period. This gives you good cash flow. You stagger the production so that you’re only harvesting a third of your system every week, and so you constantly have a product to take to the market. Your buyers are expecting something every week; it’s not like you’re telling them, “Well, I can bring it to you the first of the month, every four weeks, and you’re gonna have a bunch of it.” If you plan on harvesting the whole system just once a month… Staggering your production, I like for cash flow. These tomatoes that I put in there, they were seeded in early, let’s say mid-December. Right now, I’ve got a lot of fruit on the plant, but I don’t have anything red, nothing ready to pick yet, and here we are at the beginning of March. That’s one, two, two and a half months that I haven’t produced anything from them yet. In that same period of time, I could have had three harvests of lettuce from that area. I’ve got to envision a raft that’s four by eight feet with 60 heads of lettuce on them at a dollar each, so that’s $180 worth of lettuce that I could have produced in that time period, and I still don’t have even one dollar from the tomatoes, and I’m not sure I’m going to be able to produce $180 worth of tomatoes over the next month. So that’s why I really like the leafy green for good cash flow for an aquaponic farmer. It’s always fun to grow fruiting crops, and your customers are going to be interested in buying other products from you too, but don’t commit a large portion of your farm to those crops. You really… I mean, it’s all about cash flow. You’re paying your workers every day, you’re paying your electric bill, those are your daily costs, and you at the end of the month need to be able to pay them with the product that you’ve produced and sold. And it also depends too on cash crops, what kind of supplementation or what other things you’re doing, or if you’re growing something like cannabis, which most of us do, where you’re able to get a nice big cash crop every two or three months. It definitely depends on the crop. I think it also still kind of suffers from that same thing where, pretty much no matter what, I mean, I guess maybe the exception being clones, you’re still pretty much limited to being a cash crop every few months as opposed to having a certain portion of it now. You can’t stagger it as well. I know a lot of people do so that you’re only harvesting a third at a time and be able to do that. But I think the nice thing about greens, like you’re talking about, is that they just go so fast from seed to harvest without a lot of prep time or veg time or needing a separate facility to get them going or anything like that. It definitely still suffers a little bit from that complexity as opposed to just, you know, the simple fact of throwing some seeds out and letting them grow for three weeks, then taking them to the market. It’s pretty simple.


Speaker 1: You mentioned supplements. For some of the fruiting crops, you need to follow your spray schedule to ensure they have balanced nutrients. For example, calcium is commonly needed for squash because they can get blossom end rot. And for tomatoes, they might need more potassium because the water often has so much nitrogen that it promotes a lot of foliage growth but not much fruiting. To encourage fruiting, you need to add phosphorus. Managing fruiting crops requires more attention compared to just growing leafy greens.
Speaker 2: Right, and then indoors, you also have to worry about pollination for crops like cucumbers or tomatoes. It definitely makes it more complex, but it’s probably still necessary for the variety and to meet customer demands for different products.
Speaker 1: Exactly. Foliar sprays are beneficial not just for nutrient supplementation but also as a regular part of integrated pest management (IPM). I’ve found that it really helps boost production for both vegetable and medicinal plants. My kale, for instance, has improved in taste significantly.
Speaker 3: A lot of people make the mistake of spraying just before the plants ‘go to sleep’ when the lights go off. However, that’s when the stomata are at their smallest diameter. You really want to spray about an hour after the lights come on, when the stomata are at their largest diameter, allowing the largest molecules to enter the plant.
Speaker 1: Some might be concerned about using products like neem oil or other oily sprays, which can cause sunburn on the plants. But if you use products like Optic Foliar, you won’t have issues with burns.
Speaker 3: You also have better luck with a fogger than with a traditional water sprayer. But yes, you can still get a bit of burn, which might look similar to spider mite damage. However, the overall input result is better if done correctly.
Speaker 1: With my LED lights, they’re softer, so I don’t have as much issue with burns compared to using a 1,000-watt high-pressure sodium light, which can really heat up the plants.
Speaker 2: Speaking of lights, I lift mine up when I spray. I have an adjustable setup, so it’s pretty easy to just pull them up about three feet above the canopy.
Speaker 1: Earlier, you mentioned using silica sources. One thing I do is ferment horsetail fern, which I can harvest locally from nearly any stream. I use it as a foliar spray, and it’s great for adding silica and treating mold. Horsetail fern is a fantastic source of trace minerals.
Speaker 3: Just be cautious with horsetail fern. If used in large amounts, it can lock out the availability of vitamin B in your plants. It’s effective, but you shouldn’t use it every week.
Speaker 1: And when you make your own teas, like those from horsetail fern, there’s a lot of variability in quality. It’s hard to replicate the same batch consistently, which also makes it difficult to instruct others on how to achieve the same results.
Speaker 2: That’s the trade-off with homemade solutions. When you buy a commercial product, you get a guaranteed analysis, but with homemade teas, the consistency can vary significantly.


Steve: That’s true. It’s far less of an exact science in terms of that. The tradeoff is you can harvest it locally and it doesn’t really cost you anything. I’m just thinking in terms of the industry, you know, in building that out beyond personal scale and hobby scale stuff to actually commercialize these ideas. You need to have uniformity.
Steve: I’ve done a lot of experimenting with potassium silicate and also with silicon dioxide, which has a much lower availability. Is your pH anywhere as much? I’ve also had halfway decent luck with that.
[Music playing]
Steve: I think your microphone’s dropping out again, Stevie.
Stevie: Yeah, your microphone dropped again.
Mark: Is he gone? Oh, thank God. It took him long enough to leave. I’ve been waiting.
Mark: Alright, back to the Marty show. Mark, what’s going on with you, dude?
Marty: Oh, I’m just dowsing Steve, you know, kicking him off mike. Lemon Jack, what’s going on with me? I’ve been working on my indoor setup, getting that a little more beefed up. I have my little SIPs box here next to me that I’m feeding aquaponic water to. I don’t know if you guys can see that very well or not, but it’s a little sub-irrigated planter I have running here.
Marty: So, I added it in. It looks like Steve’s back. Yay.
Steve: Sorry about that, this man. It just gets fed tank water after I dose from the worm bin. Then I take water out of the main tank and fill it up here. Honestly, I don’t even have to do it very much. I’m just now starting to see the top of the rocks in the reservoir, and I think it’s been about maybe a week and a half or so since I added water to it. Probably going to be about once every two weeks that it’s going to end up needing water, and other than that, it’s going to be pretty much hands-off. I’ve never really done too much to it, so I like it so far. It’s a nice way to sort of expand the system, like if I’m doing water changes or taking stuff out of the filters, it can end up going into the earth boxes or right on now. So it’s pretty cool.
Steve: Okay, I think my internet stabilized. Tell me if it didn’t.
Marty: Yeah, you’re back. I don’t really know what happened there. So, the hiccup with the internet. What is the strangest or most difficult plant you guys have grown there at UVI?
Steve: Well, the most difficult plant is probably tomatoes, to get them to fruit because we have so much nitrogen in the system. The strangest plant, I’m not sure I’d call it strange, but we grow the roselle, which is used in hibiscus tea. We call it sorrel down here. It’s a red pod, related to okras, and it’s a really good crop. Another thing that’s really popular now are the bitter melons in the cucumber family. People looking for natural cures for high blood pressure eat this bitter melon, so that’s another crop. Once you target in on special needs people, then you can boost the price up. Locally produced bitter melon is a good crop for us.
Marty: I just want to clarify, when you say special needs people, you’re talking about people who specifically want a particular plant, right? Not somebody with a handicap.
Steve: Right, yeah, I was going to say, if you’re racking up the price for handicapped people… Special diets. Well, yeah, special diet people who need special diets. We raise the price for them. I mean, we want to grow a crop that’s desirable to them as well, so yeah, we would grow that.
Marty: Another crop I grew a while ago was… I can’t ever think about it. It’s slipping my mind right now. It’s not flax. We were growing it for fiber. I want to say sisal, but anyhow, we were just growing a fiber crop because you can’t grow leafy greens in the summertime as well. If you just want to kind of take a break from growing things in your system, if you can grow a crop, it’s still going to take up the nitrogen waste and do the water treatment that you need to have happen, but you don’t really have to care about the quality of the food crop coming out of it. So we were growing a fiber crop for that.
Marty: Right on. Well, I’ll know it when I say it’s… I don’t know, maybe made into rope and has a small market for some people who are into natural fibers and knitting and making their own cloth, you know, getting back to the earth, making your own clothing. So you could grow jute and basically just grow through the summertime or when you want to take some time down on your regular vegetable crop and still have something in the system because once you get the system started, you really don’t get to stop it again. It takes too long to start it up and get the fish acclimated and growing and the bacteria started. So always keep the system running even if you’re not growing a productive crop.
Marty: Yep, I was going to export those nutrients. Yes, get them out of there. What do you feel is not covered enough in aquaponic teaching or in aquaponic media as far as topics or particular problems?
Steve: Probably startup cost. People think they can do it really cheaply. They don’t want to invest that much money into it, and it’s actually a pretty intensive system. You’re taking all these unnatural components, like fiberglass tanks or lined tanks, expensive components, fitting them all together with PVC pipe, making sure the water flows the right direction. Just getting the design right are all real important things, and I think so you see a lot of systems on the internet that this will work, but they were not really tested. The really low-cost systems and how much effort goes into running a little low-cost system with low production versus putting the investing the proper amount of money into it if you’re going to be commercial and getting the returns that you’ve been looking for. If you want to quit your day job, you need to invest.
Marty: Very true, and something I just want to interject real quick and follow up on. I’ve been forgetting the whole show because you were talking earlier about how you guys steered away from media beds, and you mentioned the gravel. When I started out, I did it with three-quarter inch gravel, which, if you’ve never seen videos from Murray Hallam, he kind of talks about, and that’s where I got the idea. But after about a year, when the beds were getting a little gunked up with too much fish waste, I tried to make an air spear to blow it off the bottom easily, like I would with a hydroton bed, but that gravel, man, it was just impossible. You have to completely empty out that bed basically if you want to get rid of the excess sludge and waste. So yeah, for anybody out there that’s going to be doing them kind of media, I would steer away from it. You don’t want a headache. I would actually invest the cash it takes to get the hydroton media. It’s much easier to work with in the long run. If you have heavier plants or fruit trees you might be trying to do in the aquaponic grow bed, I guess you go with the gravel but get a solids filter in there if you’re in there to clean some of that out. You’re going to just have a headache and a half with the gravel, and every time you harvest a crop, you’re leaving roots behind. So really not good for the lettuces and things where you’re removing the whole plant every time. I always have to reach in there and dig most of them out. I feel like I can leave some of them just because of all the enzymes that are naturally in there and all the composting worms I’ve got in my media, but yeah, you got to get as much of that dead material out of there so you don’t have an anaerobic zone building up.
Marty: Yep, and hydroton’s pretty expensive, and that’s where things are, unfortunately. I know that story way too well.


Steve: Well, sorry Steve, go ahead.
Speaker: I was going to say, that’s when things like red worms and especially black worms, you know, your real small worm species, come into play to help. They won’t solve everything, but they definitely help with that situation. Another thing you can do is use other microbials. For instance, if you have a bed that you want to just clean up, you can decouple it from the system. I’ve spread out EM-1 powder, like the, um, it’s a rice flour, basically, or rice bran I guess it is, a Bokashi brand. That’s what I was trying to think of. It’s an EM-1 Bokashi brand. So, spread all that out and cover it up, and you know, in a matter of just a few weeks, they’ll eat through a lot of the solids and make it a lot easier to clean out.
Steve: We’re going to do a little myth-busting later. There’s a pretty outrageous post in the aquaponics world this week, and they just had too much bad information for us not to reply to.
Speaker: Parties, I knew you’d bring it up. I knew you had to. I was literally in tears laughing when I read this originally. It was just like, “Oh God, people actually think this stuff is real information.” You’ll never guess.
Steve: No, I’ll stay out of it then.
Speaker: Oh no, no, it’s five times… Oh no, oh yes, it was high time.
Steve: What do you see as the future of the aquaponics industry going forward, you know, in the next couple of years?
Speaker: It’s always going to be based on cities and local production, local markets. There are just too many people in the world right now. People ask me if aquaponics is going to replace conventional agriculture, and probably not for another hundred years because there are just too many people right now. The system isn’t that… I mean, it’s really productive and it’s addressing the problem of waste discharge. I think that’s probably where it’ll come in to be more impactful, like in a hundred years when we’re limited on other nutrients and we want to reclaim all we can from waste streams. But right now, conventional agriculture is really what’s feeding the world. I still look at it as high-value crops for people who really want to be part of the food supply, understand where their food’s coming from, but it’s not the general public that’s going to be buying aquaponics vegetables, paying the premium price that we need to get from our production because we have more costs than they do in just conventional field production.
Steve: What is your opinion on isolated microbial inoculants?
Speaker: These isolated microbial inoculants, like Mammoth P, which are isolated phosphorus microbes that work similarly to the nitrification process but for phosphorus, help unlock a lot of the locked-up phosphorus in the systems already. It helps make a lot of that more bioavailable. I think that’s a way that we can get a lot more nutrients out of these systems without necessarily having to worry about fish health. Mammoth P’s now, we’re creating Mammoth, and then as well, yep, those are definitely the way that things are going to be going to extract those nutrients out of the waste streams and using biological methods to do it.
Steve: For people who are new, would you be able to possibly explain what a decoupled system is, as opposed to a regular system with just a sump tank, a fish tank, and a grow bed?
Speaker: Yeah, well, instead of having it all in one system, you might have just a fish circulating aquaculture system which is producing a waste stream. Then you take that waste, aerate it, oxidize it, make sure it’s stabilized, remove the ammonia waste from it, and then feed that to a straight hydroponic system. So, the hydroponics system runs by itself, and the aquaculture system runs by itself, and the source of nutrients for the hydroponics is from the aquaculture system.
Steve: Is there ever really a risk of getting nitrogen toxicity before you can try and get the water cleaned up a bit for the fish?
Speaker: You treat the water through aeration for it might be two weeks before you move that water into your hydroponic tanks. So no, it would be… that’s why I say stabilize the water first, make sure the ammonia is all oxidized out of it.
Steve: Alright, I think I’m going to head out. If you have any more questions, let’s just check chat real quick. I really appreciate you taking the time to join us. Let’s check and make sure.
Speaker: Yeah, thanks for all the information, really appreciate it.
Steve: Alright, anyone else wrote in?
Fish Guy: No, this was all great. I learned a lot today. I’m glad I got to stay for more than five minutes for once. We’ll try and make that more of a regular occurrence. [Laughter] And thanks again for stopping in on the show today, man. Bob, I’m sure the viewers got to learn a lot of material.
Speaker: Yeah, I will listen into your podcast more often.
Steve: Alright, appreciate it a lot. Feel free to join us anytime. I really appreciate you taking the time to join us.
Speaker: Okay, appreciate the call. Have a great rest of your day, man.
Steve: Alright, bye-bye. Thank you.