From Algae to Wabbits– A Revised Aquaponic System Design

According to the Urban Dictionary, “wabbit” could be:

  1. A cuter way of saying “rabbit.”
  2. A standard Scots word meaning exhausted, tired, worn out (Ah wiz wabbit after clearin’-oot ma gearden o’ all thon leaves)
  3. Hunter’s slang for Wererabbit, or a person that has transformed into a rabbit. This word is often believed to be a mispronunciation of the word rabbit, due to a speech impediment. Unlike Werewolves, Wererabbits are in a perpetual state of rabbitness. They also have the ability to speak in a Brooklyn accent, have an insatiable appetite for carrots, and believe anyone they meet to be a doctor. These animals should be approached with extreme caution as they are extremely waskly.

I’ll explain my plans for wabbits later.

Phase I– Just get Started

The guy I had do the main concrete footers for my greenhouse, Billy, my landlord, apparently couldn’t read a drawing, even though he claims to have a degree in mechanical engineering. I’d allotted very little space for walking between the hydroponic troughs, and with him making the hydroponic area something like 18cm narrower, I had no choice but to redesign. That gave me the perfect excuse to make my plans much more elaborate, robust, and unachievable.

Building Trough #1

I’ve begun work on what I’ll call Trough #1. This will actually be the length and width that I’d planned. What’s different is that I’m making its sides out of insulated (rice husks, again) wooden panels. It’s also going to be a lot deeper than originally planned. I don’t think there is a “too deep” in raft (deep water channel) aquaponics. Because of construction costs, the question is usually, “How shallow can I make it.” Standard water depth is probably about a 30cm. The depth of the water in this trough will be about 45cm. I got lucky when I bought my 50-meter long roll of pond lining. I’d ordered a 2-meter wide roll but was given a 2.5-meter wide roll for the same price (it’s expensive stuff). Wasting building materials is second only to wasting beer in my book of no-nos. The point of making it deeper is that I may be able to use it as a fish tank in the future, allowing me to double production of fish. Trough #1 will hold about 8,000 liters of water and covers 18 square meters.

I will never use the words "final design" again. This is the latest design.

This is the new design. Technically, what I’m creating is called an Integrated multi-trophic aquaculture (IMTA) system because it will provide the by-products, including waste, from one aquatic species as inputs (fertilizers, food) for another. “Integrated” refers to intensive and synergistic cultivation, using water-born nutrient and energy transfer. “Multi-trophic” means that the various species occupy different trophic levels, i.e., different (but adjacent) links in the food chain (Wikipedia). I was kind of surprised to find that the Asia Institute of Technology (AIT) is working on a similar project.  I mean, I’m not surprised that they have an excellent idea, I’m surprised that I managed to stumble onto the same thing independently. I think there are a lot of differences, though, as they have different goals (see this link). I’ve offered to exchange information, but I doubt they will take me up on it. Academic institutions are, for the most part, owned by corporations.

I’ve actually got a better idea for plumbing it. Fish tank water will flow by gravity to the solids removal tank. In the diagram at the right, I’m using 3 concrete rings. The bottommost ring is mostly buried and has a 45-degree taper down to a pipe for removal of the solids. These solids, fish waste and uneaten fish feed, are an important part of the system, so I want to access them efficiently. The diagram shows 1-meter diameter rings, but I’ll probably use 1.2-meter rings. Can’t be too big. The system water will continue to flow by gravity into Trough #1. I was going to have it set up to flow into Trough #2, too, and then both troughs would drain to sump, but I’m now considering flow into only Trough #1 and then from Trough #1 to Trough #2. So, all the system water will exit Trough #2 to sump. As it’s shown, I’ve got 2/3 the plant growth area of my former design. This is probably okay depending on the fish feed (g) to plant growing area (m2) ratio. Since I’ve got 36m2 plant growing area, it will support 2.16 to 3.6kg of fish feed input per day. As an example, if I had 400 adult fish in the tank and they each weighed 800g, then the total would be 320kg of fish. If they were fed 1.2% of their body weight each day, that would be 3.84kg, but, not to worry, the vertical, or hanging plant growing component (upside down tomatoes and bell peppers) is not shown here. Besides, it’s going to be a play-it-as-it-goes thing, anyway. If I have problems, I’ll harvest some fish, or add some, as necessary. I’ll go quickly now through the two new components I’ve added (excluding the sexy intern).

Algae

Spirulina, a dietary supplement for my fish.

Spirulina (Arthrospira platensis) is widely known as a dietary supplement (miracle drug). There are all kinds of edible alga, but spirulina sort of takes the cake. Its nutritional profile is outstanding (60% protein), and since it actually thrives in highly alkaline water that other types of algae cannot withstand, it can be monocultured by keeping the PH high. For this reason the culture water for the spirulina will be completely independent of the aquaponic system water.

Spirulina can be harvested with a very fine mesh cloth.

Normally, spirulina is fed a complicated mixture of nutrients plus CO2. I’m not going to be too scientific about it, as I’m not trying to get maximum yield, so they will get some of the waste solids I remove from my system (a bit like putting manure in a pond to induce an algae bloom) including some system water to make up for evaporation, ordinary aeration (until my mushroom growing rooms are built, then they will get CO2 enriched aeration), and perhaps some ordinary urea (I’ll resist the urge to pee in the algae troughs). Spirulina can be harvested easily as the photo shows, another advantage. 10g per square meter would be a mighty fine daily harvest generating 120g per day. That’s only 2.5 to 5% of my feed needs, so you may wonder if it’s worth the space, but it’s got double the protein of standard feed and provides other goodies. Also, if I were to eliminate the shallow algae ponds and extend Trough #2, I’d have to extend the aisleway, too; as it is, I figure that boards could be laid on top of the algae ponds for access. So, I think I’m saving 4 to 5m2 of productive floor space.

A type of algae that's easy to culture, but difficult to harvest.

Chlorella is another algae I’ll be playing with. It’s also available as a dietary supplement, but not quite as popular as spirulina. It’ll be fed the same fish waste and maybe some urea if needed. Both of these types of algae have been studied for their ability to remove nutrients from and thrive on fish effluent, so I’m expecting it to be pretty simple to grow them– but I don’t want much of either of them going directly in my system, so chlorella will be (mostly) independent, too. Studies have shown that chlorella is suitable as the sole source of food for Thai fairy shrimp, but  I’ll discuss that in the section below. Spirulina is also consumed by the fairy shrimp, but the studies suggest it’s not up to par. Chlorella will be grown in 5-liter clear plastic PET bottles hanging from the central greenhouse structure as well as in the concrete rings holding the fairy shrimp.

Fish feed is expensive and its origins are a bit dubious, so the goal is to produce a nutritious and tasty fish feed myself. Spirulina are easy to harvest, so they will go directly into the feed, while chlorella, which is difficult to harvest unless you are a larger aquatic animal, will either go into the feed via the fairy shrimp or directly into the fish via the fairy shrimp.

Thai Fairy Shrimp

Their environment made these guys perfect for aquaculture.

I need a drum roll and somebody to sing Elton John’s “Circle of Life.” These critters are truly amazing. Thai fairy shrimp (Branchinella thailandensis) were discovered by some university researchers who were splashing around in some vernal pools (temporary pools of water that provide habitat for distinctive plants and animals) in Northeast Thailand (my backyard). If you choose a vernal pool as an abode, and you need something to always be able to swim in, you’re out of luck. But fairy shrimp (technically they are micro crustaceans) have managed to survive by growing quickly (reaching sexual maturity in just a week), an ability to reproduce which puts wabbits to shame, and the fact that their eggs (cysts) don’t mind it if the pond dries up– they’ll just stay put until the rains come again. They were only discovered about 10 years ago, but they are already becoming a big business. Why? Because they reproduce rapidly and have high nutritional value. Here is a somewhat random introduction from one study:

Fairy shrimps have great potential as live food organisms for a variety of aquatic animals. Both larvae and adult fairy shrimps (live or even frozen) can be fed to commercial aquaculture species such as catfish and shrimps and other aquarium species such as flower horn (Boonmak et al., 2007). The cysts of fairy shrimps contain 45-50% protein and 5-6% lipids while adult fairy shrimps have higher protein and carotene contents. Fairy shrimp biomass produced (using livestock waste as a nutrient source) can be used as nursery and maturation feed for ornamental fishes (Munuswamy et al., 1997).

It has also been shown that fairy shrimps contain high levels of many essential amino acids which are important for the growth performance of fresh and brackish water fishes and other crustaceans. Through enrichment and bioencapsulation,
fairy shrimps can be an ideal candidate for the provision of
valuable nutrients to young larvae of commercial aquaculture species (Munuswamy, 2005). Their high carotenoid content also makes them ideal for color enhancement in ornamental fish culture.

With the high cost of Artemia cyst to provide a good source of protein for freshwater and brackish fishes, the government of Thailand restructured a financially viable agendum by conducting research on the production of fairy shrimps (Branchinella thailandensis Sanoamuang, Saengphan and Murugan, 2002) which are locally available (Saengphan and Chusing, 2006) in the country.

This photo of the laboratory at Khon Kaen University is revealing.

One of the advantages cited in many studies is the fact that fairy shrimp are easy to culture. Yeah, right, but nobody wants to let the average guy know how. It’s not like the Food and Agriculture Organization of the United Nations is publishing cultivation manuals for us peasants.  Not surprisingly, the academic institutions are making the information on culturing fairy shrimp and harvesting their eggs (cysts) available to businesses for a fee. But they still have to gain legitimacy by publishing their studies, so the information is out there, if you are willing to work for it. It’s made harder by the fact that usually only the abstracts are available; you have to pay do download the meat and bones of a study. After reading through a plethora of papers, not to mention following threads on the subject in all the amateur aquarist forums, here are the important points that I’ve learned.

  • “The prawns [giant freshwater prawns] with the greatest weight and length were those fed 50 live Thai fairy shrimps (30.07±0.16 g, 12.14 ±
    0.09 cm, respectively).” So from this I learned that a mature (7 to 8-day old) fairy shrimp weighs approximately 0.6g.  I also know that they are just over 12mm in length. You wouldn’t believe how hard it was to find this information.
  • From another source I learned that Branchinella thailandensis can be cultured outdoors at a density of 50 nauplii [hatched baby shrimp] per liter in concrete rings that are 1 meter in diameter and hold 150 liters of water.
  • A female of the Branchinella thailandensis species will produce up to about 6,000 eggs (cysts) in her short lifetime (about 1 month).
  • Perhaps most importantly, truly a great find, was the knowledge that, specific to Branchinella thailandensis, “The cysts require a period of retention in the parental medium for 2 – 4 weeks in order to continue their embryonic development before hatching.” And, “In contrast to the hatching behavior of many other species, drying is not absolutely essential for cyst hatching of this species.”

Commercial scale production-- the method was developed by the rich lady in the photo above.

The tricky part is harvesting the eggs. If you don’t do your homework you will likely believe, as many amateur aquarists do, that you have to dry the eggs, refrigerate them for a while, then put them back in water to hatch. They use distilled water, but if I were a fairy shrimp egg I’d wonder what the point of hatching out into that would be. Anyway, having learned that (a) the particular species of fairy shrimp I’ll be dealing with does not absolutely need drying out, and (b) they do, however, need to stay in the the water for 2 to 4 weeks, I’ve decided it’s worthwhile giving them a shot. Incidentally, one could just keep buying the eggs and not worry about recreating little orange populations. 1 million eggs can be purchased from a Thai company online for $165. But, assuming the unlikely scenario in which every one of them hatches and they all grow to be 0.6g, even though that’s a whopping 600kg of fairy shrimp, they are, unfortunately, composed mostly of water (90%, in fact). So you’ve really only got 60kg dry weight. That’s $2.75 per kilogram. While it’s certainly more nutritious than commercial fish feed, it’s also more than double the price. So, they are either going to have to reproduce in situ or piss off.

The polyculture of tilapia and giant freshwater prawns will eat these at any stage.

The system layout in the illustration above shows only thirteen 80cm diameter rings, but I need more if I’m going to make this work. So, I think I’ll partially bury these such that the water level in them is just above the water level in the sump and place a staggered  row of 12 rings on top for a total of 25 rings. Each ring will hold about 150 liters of system water. Water will be trickle fed such that an exchange of about 20% a day is achieved. Fairy shrimp eggs come in capsules, and each capsule contains 10,000 eggs ($25 for 120,000 eggs, 12 capsules). That’s a good number. At a hatching rate of 75%, that will give me the magic number of 50 fairy shrimp per liter per concrete ring. We’ll call this first one Ring #1. The next day I’ll stock Ring #2, and so forth until all the rings have been stocked. The fairy shrimp cysts will wait until they are certain that it wasn’t just some freak rainstorm in the middle of the dry season before they hatch, but by 10 days after stocking Ring #1 I should have 7,500 healthy snacks for my fish and giant freshwater prawns (in polyculture). At 0.6g each that’s 4.5kg of 12cm-long goodies. But, in terms of dry weight, that’s only 450g. With a protein level of roughly 60% of their dry weight, though, they are worth a kilogram of fish feed. In a perfect world, I would harvest 90% from one concrete ring a day just as they are full-sized and have reached sexual maturity. Having reached sexual maturity, the boys will spend all their energy doing what boys do best, and the girls will become egg producing machines. If I leave 10%, essentially I’ll be leaving 375 females. In her lifetime, each female will produce up to 6,000 eggs. At even 4,000 eggs each, that’s 1,500,000 eggs that will be laying dormant at the bottom while their embryos continue to develop. If all goes well, by the time I’ve stocked Ring #25, these 1,500,000 eggs will have hatched and madness will ensue. But they won’t all hatch. And to a fish or a larger shrimp, a 1mm fairy shrimp will be just as tasty as a 12mm one. The whole thing is bound to break down into a situation where I’m just removing some biomass, in this case fairy shrimp of various sizes, from some of the tanks each day, amassing an unknown number of them but, nevertheless, at least 4.5kg a day.

With double the carotenoids, my giant freshwater prawns will be a brighter orange than these.

How am I going to feed them to the fish and prawns, you ask? Probably just as they are. Tilapia are omnivorous so unless they’ve been brainwashed by the vegan community, they should be perfectly happy eating the micro crustaceans. I’ll be stocking giant freshwater prawns with the tilapia (3 individuals per m2) and in the plant growing troughs (10 individuals per m2). Many trials have been done using fairy shrimp as the sole source of feed for these big fellows, and not only superior growth has been proven. Major improvements in quality such as a much higher amount of carotenoids, in particular, was shown. The prawns fed fairy shrimp were visibly a brighter orange. I wonder if it will affect the flesh color of my tilapia, making it resemble salmon. . . Anyway, I don’t see the harm in just throwing them into the system. The ones that survive the fish tank and seek safer shelter will pass by gravity to the solids removal tank where they can’t do any harm. They may like it there so much that they decide to stay and populate it, but they should be warned that there will be a few small tilapia in there to clean the sides. If they flow from there into Trough #1, they’ll regret it. There will be 180 giant prawns waiting for them. If they manage to out swim these prawns, there will be another 180 waiting for them in Trough #2. A fine mesh bag under the outlet to sump will catch any unlikely survivors. The ones that stay in the piping will be doing me a favor by cleaning up detritus, algae, and such. The whole thing will mimic nature, just exponentially more intensive.

An alternative would be to dry them and mix them with the spirulina (also dried) as the protein component for the production of an on-farm feed. That’s a lot of work, though, and they would lose some of their nutritional value (prawns fed frozen fairy shrimp, for instance, did not do as well as those fed fresh ones). I want my prawns and fish to lead lives as they would in nature, but with greater abundance. I suspect that life for a giant freshwater prawns is pretty dull just waiting around for somebody to throw them a handful of pellets. There’s no sport in plucking up a pellet that has sunk to the bottom and landed right in front of your rostrum, no spirit of the chase.

Phase I– The Strategy

Harvesting rain.

As I write, the fish tank is filling with rainwater. I can’t afford to have a well drilled at the moment, so I have to harvest rain. Luckily, there’s no shortage of rain on the Bolaven Plateau at this time of the year. The one tarp I put up increases the surface area a little, and the tarps covering the tank lessen losses from evaporation while still letting water in. I have an elaborate scheme for harvesting rain, as you’d suspect, but I’ll spare you the details. I’ll need another 8,000 liters when Trough #1 is completed.

Fish

Recommended stocking and feeding rates for different size groups of tilapia in tanks and estimated growth rates.

As soon as the tank is mostly full of water I’ll adjust the pH if necessary, add some pig manure (for now I’m letting Billy keep his pigs on my leased land), and throw in an algae starter to get a healthy, light-green pea-soup going. I’m not particularly worried about algae in the system at this point. When the time seems right, but as soon as possible, I’ll stock it with 1,000 tilapia fry. Under normal circumstances, that would be too many fish for my system, but that’s the minimum order quantity for monosex fry. Deviating from my past strategy, I’ve decided to live with this number and practice a combination of gradual thinning and graded harvesting. The fry are just 2.5cm long and weigh only about 0.25g each, and they’d lose touch with each other in the spaciousness of the 8,000 liter tank, so I’ll keep them in hapa, which is really just a fine mesh cage, within the tank. As the table here shows, in a little over 2 months they will weigh about 20g and need to be fed about 7% of their body weight. With 1,000 fish, that’s 1.4kg a day. That’s when I should start getting the plant growing area (Trough #1) going.  In another month they will have reached 50g and will be eating 4% of their body weight per day. That’s 2kg of feed a day being consumed. It will be time to start plants on Trough #2. Roughly 3 to 4 months after having arrived on the Bolaven Plateau, the finned fellows will have reached a weight of 100g but they will still have plenty of room in the tank. In fact, they really need only about 1/4 of the tank at that stage. It will be the end of the exponential growth phase and the beginning of the linear growth phase. They’ll be eating a total of 3.5kg a day which is just fine. When they reach 250g about 7 weeks later, they’ll be eating only about 1.5% of their body weight daily, so at 3.75kg of feed a day, that’s still okay, but they’ll be at the maximum recommended density in the tank. Incidentally, the tilapia in the table seem to grow slowly compared to raw data I have from the supplier for the particular breed I’ll be raising, but the stocking densities should still be accurate.

Fish are mostly eaten whole in SE Asia.

The obvious solution to overcrowding is consumption. If the mean weight of the fish is 250g, that means I’ll probably have fish that range between 200 and 300g. A 200g fish is more than 20cm in length. In the West, they have to be grown out to a certain size to accommodate fileting, but here in Southeast Asia they eat the entire fish, including the eyeballs. Large fish are expensive, 30,000 kip ($3.78) on the Plateau, probably due to the cost of transporting them up from Pakse. I suspect five 200g fish would fetch the same price as one 1kg fish, but at the moment, I’m not sure. Anyway, in terms of strategy, I’m simply going to start harvesting the smaller fish at this point such that the total feed per day stays below 4kg. This is also probably a good point to stock another 1,000 fry in a hapa, sacrificing 1m2 of Trough #1 grow area.

By the time the mean weight of the fish is 450g, and that will happen more quickly if I’m removing only the small fish (I’ll do this because it’s better to hold on to the fish that demonstrate good growth), I’ll want there to be no more than 800 fish in the tank. Assuming that it takes 8 weeks to reach this stage, it’s just a matter of removing 25 to 30 fish a week. If the fish removed are, say, 250g each, then that would instantaneously lessen the daily feed load on the system by about 100g. It would also provide my venture with its first income, a whopping figure in the area of 200,000 kip ($25). But the fish the next week will be bigger. By the fourth week I’ll probably be selling 350g fish, fetching me around 300,000 kip ($38) which is enough to satisfy my Beer Lao needs (a little over 3 cases a week). Meanwhile, the bigger fish will be getting even bigger. By the time they’ve reached a mean weight of 450g, they’ll be at the recommended stocking rate, so it will be time to thin them and also make some room for the 1,000 juveniles kept in Trough #1. The 450g fish are at a marketable size, and in the course of 8 weeks they will reach about 750g. When they get that big there should not be more than 50 of them per cubic meter. They should be all sold by the time the second cohort reach 250g because they’ll need all the tank space. I’m not sure when that will be, but lets say for the sake of argument that I sell them over an 8 week period, and then the new cohort is thinned by about 200 individuals over a period of 6 weeks:

  1. 450g x 100 = 45kg @ $3.78/kg = $170
  2. 485g x 100 = 48.5kg @ $3.78/kg = $183
  3. 520g x 100 = 52kg @ $3.78/kg = $197
  4. 550g x 100 = 55kg @ $3.78/kg = $208
  5. 580g x 100 = 58kg @ $3.78/kg = $219
  6. 630g x 100 = 63kg @ $3.78/kg = $238
  7. 690g x 100 = 69kg @ $3.78/kg = $261
  8. 760g x 100 = 76kg @ $3.78/kg = $287
  9. 200g x 30 = 6kg @ $3.78/kg = $23
  10. 250g x 30 = 7.5kg @ $3.78/kg = $28
  11. 300g x 30 = 9kg @ $3.78/kg = $34
  12. 340g x 30 = 10kg @ $3.78/kg = $38
  13. 380g x 30 = 11kg @ $3.78/kg = $42
  14. 420g x 30 = 13kg @ $3.78/kg = $49

At week #15 it starts over again for roughly 3.5 cycles a year. The total of the above is $1,977 so that would be close to $7,000 a year. Of course that’s highly unlikely. There will be mortalities and I doubt I’ll be able to sell them at such a price. But, even knocking off 35% for these and other unknowns (fudge factor), that’s still a nice $4,500 gross income for fish in just an 8,000 liter tank.

Freshwater Prawns

I’ll stock juveniles in both the plant growing tanks, and maybe a few in the fish tank. Unlike the fairy shrimp, they cannot reproduce in fresh water, so there’s no worry of an overpopulation problem. I’m tentatively considering stocking 10 individuals per m2, so that would be 360 of the tasty crustaceans. For the most part they will be fed on whatever they can get from the system, but I’ll give them some fairy shrimp from time to time. They may get some anyway if the fairy shrimp make the trip from the fish tank. I’ll be happy if I can get 20kg of them 4 to 6 months after stocking them. That would be worth only about $170 so I’ll probably just eat them myself from time to time, occasionally restocking. This isn’t really a commercial venture during Phase I; it’s more for their functional activities, cleaning up detritus and adding to the biodiversity.

Plants

Don't freak out, they're just tomatoes growing upside down.

There are so many possibilities it is hard to decide, and I really don’t have to yet. I’ve got 3 types of lettuce seeds from the US which I’ll experiment with first. Trough #1 can hold 360 lettuce plants, and the growth cycle takes 4 to 5 weeks, so I can expect a minimum of 10 harvests a year. That’s 3,600 heads and, at approximately 250g per head, 900kg a year. Using the very conservative figure of $2.50 per kilogram, the lettuce in Trough #1 will bring in $2,250. It would make sense to do lettuce in Trough #2, too, if I can sell it. Hanging from the wooden joists running down the center of the system, I’ll grow tomatoes and bell peppers, upside down, of course, because it will freak people out. My earlier estimates were 300kg and 230kg a year, but I’ll lower those figures by a third to make space for PET bottles of algae (for the fairy shrimp). I should be able to get $2.50/kg for the tomatoes and $4/kg for the bell peppers, so that’s about $500 and $600, respectively.

Phase I– Summary

  • Fish production = $4,500
  • Plant production (lettuce, tomatoes, and bell peppers) =$5,600
  • Total = $10,100

Phase II– Bringing it Outdoors

Mean monthly temperatures on the Bolaven Plateau.

While doing my hermit thing I made a feeble attempt to keep track of morning, afternoon, and evening temperatures. Beer in the evenings inhibited taking accurate records, and I just plain forgot to do it most days. In the shade in the afternoon the temperature reached about 25C most days, and in the morning the coolest it got was 19.5C which, in theory, is the average mean temperature. Somebody has already done this work for me, so I was really just checking the accuracy of the data shown here which I took for the FAO’s Arabica Coffee Manual for Lao PDR. The red line, Km 42, is just 2 or 3km downhill from me, so it’s closest. I don’t know why Km 34, the yellow line, is so much cooler. It’s at a lower elevation. I suspect that it’s got something to do with the landscape there, like being bowl-shaped such that cool air collects. Anyway, with mean monthly temps between 19 and 23C, it’s what the technical people call “damned comfortable.” It’s actually made me wonder why I’m building a greenhouse, anyway. . . Oh, yeah, the fish. The tomatoes and bell peppers will enjoy the heat, too, but most other things, like lettuce, will be happier outside where it’s cooler.

There are a few problems with growing things outdoors, but these are not so difficult to overcome if you are enough of a lunatic to try some new approaches. The advantages of growing outside justify a bit of odd scheming. The first problem is that my system water temperature will be (should be) around 25 to 26C. That’s to provide for happy, fast-growing fish. You can’t take advantage of the cool outside climate for growing things such as strawberries if you are pumping 26C water into their root zone. Once I know how much water the outside component needs, I think I can solve this problem by leaving the water out overnight in an uninsulated tank. By morning, the water should cool down to 20C or so, depending on the season. First thing in the morning the tank could be wrapped with some sort of blanket insulation which would keep it cool for the day. On the return side, the opposite could be done. Return water would be passively heated by passing through black LDPE tubing and into a black tank. It would be insulated at night and gradually returned to the sump in the greenhouse. A lot of hit or miss here, but I’ll eventually sort it out.

Hydroponic strawberries growing in towers in California.

The ever-so flattering description of me as being “Insane. Cracked. Done for. A complete fruit loop” will no doubt be applied to me again when Ross, my mate from Down Under, arrives in Vientiane next week. Designs like this are, however, only crazy on the surface, and I can’t be accused of coming up with the idea. Vertical growing is all the rage these days amongst we lunatic farmers. The farm shown here can grow 12.5 strawberry plants per square meter, producing 17kg in this small amount of area.

Bringing it Outdoors– The Strategy

My soil is excellent for growing coffee so I don’t want to waste any more than I have to on grow beds, tanks, etc. After the coffee harvest at the end of this year, I’m going to replace the struggling katimor variety of coffee with typica which has a better cupping quality on an 8 x 20m patch of land next to the enclosed aquaponic system. The existing trees are struggling because they get too much sun and are spaced too close together. None of the coffee farmers read the FAO coffee manual– they just figure: the more coffee trees, the more coffee. I’m going to give these young plants 2 meters to spread their roots. Between the rows I’ll plant perennial peanut (Arachis pintoi), a leguminous forage plant which grows well in the shade and fixes nitrogen. So, there’s really no room for ground-supported towers like the ones shown above; instead, I’ll use hanging towers.

Hanging towers full of strawberries, lettuce and other vegetables will provide shade for the coffee.

The hanging towers will be constructed of white PVC tubing. The inside diameter will be 120cm and the long ones will be 1.33m in length. They will be filled with coir (coconut husks) so hopefully not too heavy even when wet. Hung from about 3 meters from the ground, the towers will be above and between the coffee, getting the most sun and providing shade. The longer towers will hold 15 liters of coir, and the shorter ones (half the length), will hold 7.5 liters of coir. While I personally favor raft aquaponics, with plants floating on the water, I couldn’t figure out a way to make water float above the coffee trees, so I’ll be entering into the world of media-based aquaponics which, it so happens, is much more popular with the backyard hobbyist folks. As a rule of thumb, they aim for a 1:1 ratio of fish tank volume to grow bed (media) volume. At the scale shown here, there are 50 long towers, so that’s 750 liters, and 75 short towers, so that’s 563 liters for a total of 1,313 liters.

This would suggest that I can only increase fish production by how many fish that can fit in a 1,313-liter tank. So, rather than follow this rule of thumb, I think it’s better to consider how many plants can be grown (nutrient uptake) here. If I grow strawberries in the long towers at 20 plants per tower that’s 1,000 strawberry plants. If I grow lettuce in the short towers at 15 lettuce plants per tower that’s 1,125 plants at any given time. If these were grown horizontally on rafts, I’d need 56 square meters for the lettuce alone. Assuming the same needs for the strawberries, I’m at 112 square meters. So, if I keep Trough #2 full of plants, can I really double fish production by making Trough #1 a fish tank? The answer, I think, is a definitive “yes.”

If grown horizontally, the area required to grow all this stuff would be 130 square meters.  Since the feed/plant area ratio demands at least 60g of feed per square meter, that’s 7.8kg of feed a day. Pretty much double Phase I. So, not only can I double fish production, I can raise it some more. The seemingly unused area where the pretty intern with nice tits is standing is for raising seedlings and such. There is no reason this cannot be done on tables above fish tanks. My favorite hardware store in Ubon sells 2,500-liter circular tanks. Two to 4 of these would fit nicely in this area. I’ll be certain to tie them securely in my truck (those of you who read my last article will understand why). Two smaller tanks plus converting Trough #1 into a fish tank would facilitate 2.5 times more fish. Assuming a 15% mortality rate and a food conversion ration (FCR) of 1.4, I’ll be supplying 115g per square meter of plant grow area. Considering the fact that I’ll still be growing tomatoes and bell peppers inside the greenhouse, I think this will be acceptable.

Anyway, this transition will be slow and carefully done. I can gradually expand the number of fish in Trough #2 and gradually put up towers outside.

Phase II– Potential

I’ll use lettuce to count my chickens before they’ve hatched, but most plants should thrive outdoors. I’m excited about strawberries. A 1-meter wide “roof” above each row of towers, made out of left over greenhouse plastic, will keep the rain off of them but still allow the water to saturate the ground for the coffee and forage. Among other possibilities is watercress which will thrive in the cool climate. I don’t eat strawberries myself, but they are grown in the north of Thailand and fetch a very high price. At a pick-your-own farm near Chiang Mai, people pay an entrance fee and 250 baht ($8) per kilogram. I could rent out ladders and charge the same, but people will have to beware the wabbits.

  • Fish production = $11,250 (already reduced by 35% for losses, etc.)
  • Plant production (lettuce, tomatoes, bell peppers) = $10,381
  • Strawberries (at 1kg/plant) = $8,000
  • Total = $29,631

Phase III– Wabbits

16m2 per doe and her offspring-- spacious living and good food in return for yummy meat after a short lifetime.

As much as I like pigs for their intelligence and sense of humor, they are big fellows who may not treat strawberry pickers nicely. My piggy adventure will continue, but in Vientiane where there won’t be strawberries dangling overhead. Rabbits, on the other hand, produce what is arguably the finest manure for the manure aficionado and it requires no composting to use. If I were walking around in an animal pen picking strawberries, I’d certainly rather step on a pelleted piece of bunny poo than a steaming pile of pig dung. Rabbits are also the most economical, labor-efficient, and practical way to produce protein.

Each doe will get one 2 x 8m run. The runs will be divided by simple wire mesh fencing (chicken wire). It will protect the trunks of the coffee trees as rabbits like to gnaw on things but still allow socializing, if desired, with the female and her offspring in the next pen. This will give me 9 pens for does and 1 pen for a buck. I took a crash course in rabbit farming and I’m convinced they are just what I need to fertilize the coffee trees and mow the grass (high-protein perennial peanut).  A mature doe will produce 8 to 10 kits (offspring) in just 30 to 31 days after mating. These will be “fryer” size, about 1.5kg, in 12 to 15 weeks. In the meantime, you can begin the routine again for up to 5 litters a year. At an average of 8 kits per litter the 9 does would produce 540kg of rabbit a year. Assuming their live weight has the same value as a chicken, that’s another $2,366.

The investment is minimal. I’ll put chain-link fence down on the ground which will prevent them from burrowing yet allow the perennial peanut to grow. The chicken wire fencing between the pens can be low enough to step over. Any rabbits that get over it will not be able to get through the perimeter fence (electric) which will hopefully keep 2- and 4-legged rabbit thieves out (this will help protect my greenhouse and hermit house, too). Incest in the rabbit world isn’t a problem, so you can start with a buck and 2 does and choose the best females from the resulting litters.

The problem will be marketing. Reading about rabbits on an expat forum in Thailand, most of the guys who suggest they raise rabbits to their spouses are treated to an emotional outburst of significant proportions. Rabbits are cute, cuddly pets, not dinner. And that, itself, is a potential market (rabbits don’t make noise like pigs and are easy to conceal, so I’d probably have no trouble smuggling them into Thailand for the pet market). Perhaps the Thai revelers who come pick the strawberries, aghast at learning that the cute bunnies at their feet are being raised for meat, will pay a premium to rescue a few. The large Vietnamese population in the area will appreciate their availability. Ideally, I’ll supply one or two good French restaurants in the city (Pakse). If this happens, I’ll have to increase rabbit production, and that wouldn’t be hard to do.

They didn't know that rabbits are easy to skin. They singed the fur off of them.

Admittedly, the Lao people will eat anything. Rabbit is not common, though. Actually, that’s an understatement, because, according to a survey done in 1997, total rabbit production in Laos was just 500kg. Things have changed a lot since then, though. My little Lao helper is holding up 2 rabbits that her cousin was keeping. They escaped from their pen and were seized upon by local dogs. I considered them unsafe to eat, and when they started searing off the fur as they do with rats and such, the smell overwhelmed and I left. They didn’t know that rabbits are easy to skin (I didn’t either, at the time).

A paper entitled “A Strategy for the Development of Small- and Medium-Scale Rabbit Farming in South-East Asia,” after citing studies that have shown the potential of rabbit production for small farm family development, goes on to state:

This era of potential is now history because the benefits of rabbit production to smallholders have been realized in many lesser-developed countries (LDC’s) throughout the world. The present challenge is to take the rabbit to a higher level– to usher in a new era that involves formulation of new and improved models for development projects to provide even greater benefits for limited resource families, especially when initiated as a vehicle to alleviate poverty.

For a poor farming family in Laos, the loss of a breeding cow, pig, or goat may be catastrophic. The paper states that rabbits have a competitive edge over poultry in Asia as they do not depend on cereal grains (human food) and, of course, there’s no worry about the risks of Asian Bird Influenza.

Without getting into too much detail about animal cruelty and such, it is interesting to note the fundamental differences between animal cruelty law in the United States and Europe. In the US, a farmed animal is valued as a piece of property or a machine. In Europe, however, the laws reflect the view that animals are sentient beings. A paper on the subject states:

It can be seen that many common US husbandry practices are being phased out or have already been banned in Europe. The cruel practices that are considered common in the US are becoming violations of animal welfare regulations across the Atlantic. This is due to the status of animals. As property, animals may be treated like machines, regulated mainly for the benefit of the owner. As sentient beings, animals are endowed with a moral status and human beings have an advanced role in the protection of these beings. In the United States, there is a huge agricultural lobby. Food animals are governed by big money industry; most regulations are designed to protect this industry. In a union of countries such as the EU, a door is opened to newer ideas about the role of animals and their relationship with humans. In Europe, there is a variety of lobby’s controlling the regulation of animals. Although some countries are still faithful to the Christian idea that we have dominion over the animals, several other countries have moved away from this, believing that animals need to be protected for their own sake. This explains why the EU regulations are shifting. Several EU member states no longer hold the view that animals only have value as property. Animals cannot be given a moral status and still be treated as though they have none.

Switzerland has the toughest laws. In fact, rabbits are defined as “social” animals, so it is illegal to keep only one of them. They are sold with a companion. It’s a problem if one dies because according to the law you are required to replace it and there’s no guarantee that they will get along. Considering that an area of slightly less than a half a square meter is required for a single rabbit, a doe and her 8 kits will have an area of 1.77m2 each to hop about in, which will make them exceptionally lucky animals until the abrupt conclusion of their short lives. I’ll add some substrate here and there such a logs to jump over and tunnels to enter (20-liter pails placed on their side and partially buried). It’ll be more like a petting zoo than an animal farm, but with a coffee plantation there’s no need to raise them densely.

Feeding the Wabbits

I’ll devote Trough #2 to the production of water spinach (pak bung). Studies have shown that water spinach is an excellent feed for rabbits and satisfies all their nutritional needs. They’ll also feed on the perennial peanut growing in the play area. But that’s still not enough to produce 520kg of rabbit meat a year. The feed conversion ratio for rabbit is something in the area of 3.7, so they will need about 2 tons of feed dry weight. Since water spinach is about 90% water, I’d need 20 tons of it. Trough #2 will produce only about 1 ton green weight a year. I’ve calculated that the forage in the pen areas will only provide enough food for 20 rabbits, which is about how many the water spinach can support. There will also undoubtedly be a lot of waste greens. I’ll consider that as enough for 20 more rabbits. That leaves 350 rabbits to feed. As I gradually replace coffee trees, I can expand on the area for them to graze on perennial peanut, sort of managed intensive rotational feeding on a small scale, but I intend to do this slowly, and there are costs involved (chain-link fencing on the ground, etc.).

The solution is cut-and-carry forage. There’s plenty of grassy, weedy stuff growing around, but since I don’t know which ones are safe for rabbits, I think it’s better to grow a high-quality forage. In a Laos-specific paper I read entitled “Evaluation of Tropical Forages as Feeds for Growing Rabbits,” it was concluded that the leguminous Stylosanthes guianensis (Stylo 184) was the best forage material of the ones available in the study. But an even better forage is Ubon Stylo. I can expect 15 tons of dry matter per hectare per year and 15 to 20% crude protein. Since I need about 1,300kg of dry matter, I’ll need to cultivate about a 10th of a hectare, or 1,000m2. That’s just 32 x 32m. I’ve got plenty of space down on the second tier. For good measure, I’ll cultivate another 1,000m2 area with Mulato II which is a type of forage grass with a similar protein content. It is supposed to be highly nutritious and digestible.

In less than two weeks I return to the Plateau, my little Lao helper and our offspring in tow, to finish Phase I. The system should be up and running, cycling with fish in the tank by the end of August.

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2 Responses to From Algae to Wabbits– A Revised Aquaponic System Design

  1. michael hare says:

    Excellent reading Richard.

    Some years ago I was on a technical mission in New Caledonia. It was out in the country and it was Sunday. Only one restaurant was open. Stopped for lunch and my French hosts ordered rabbit stew and rabbit that. Problem was the rabbits had to be killed, skinned and then cooked. Took ages.

  2. ross says:

    After two days reading,I finally finished the Blog.Conclusion:You are still insane.
    I will need to sort this out again next week and it is getting tiresome. Just how much Beer Lao and Vodka does it take to keep you balanced?Last time my good work lasted for a full bloody week before you went off the rails but, me fears, it may take another marriage, harder drugs, a massive financial windfall, and/or a step on a UXO get you back into reality. And NO,I ain’t marrying you.(as much as I like rabbit, fish,strawberies, coffee or whatever the latest Boston craze may be)

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