Friday, September 18, 2009

Future Fish’n’Chips (Part I)

Building Belize’s first solar powered aquaponics system… and why that's mouth-watering

‘Aqua what?’ would be a reasonable response but you may well be hearing this word a lot more over the next few years. One short answer is aquaponics as ‘promise’: the promise of cultivating delicious, organic fish and vegetables in a small space with minimal work; the promise of a major role in the next great step in human agriculture (forwards this time) in which we use our technology to make the most of nature’s intelligence rather than to ride roughshod over it; the promise of eating without eating into our future.

That’s a lot to live up to, yet we need some big answers to the big questions we face: how to feed ourselves as we approach 7 billion and the precipitous production drop in easy energy from oil and gas? How to save our precious topsoil and end the strip-mining of our oceans? Where will the water come from? [1] [2]

Could aquaponics grow into one of these big answers?

For millennia fish have been cultivated in captivity, raised in ponds or tanks as a food source.[3] This ‘aquaculture’ is effective but has always struggled with the sludgey problem of poop: fish defecate in their water until it kills them and so the water needs to be changed regularly. That can mean a LOT of water.[4] And since the early twentieth century vegetables have been grown in a liquid solution rather than in soil. This ‘hydroponics’ can be wonderfully productive but those plant nutrients have to come from somewhere - normally bought as a pre-prepared formula – and systems can also experience problems with disease, as all the plants are sharing the same solution. [5]

In a lovely example of the much sought ‘win-win’ you can combine the two, aquaculture and hydroponics, into aquaponics and their respective flaws are canceled out. By growing fish in a tank and cycling their water through plant-filled grow beds you create ideal growing conditions for the plants, which then clean and oxygenate the water ready for its return to the fish.

The result, according to the aquaponics evangelists, is an incredibly productive system. Joel Malcolm, founder of, reports a six month crop of “50kg of fish and hundreds of kilograms of vegetables” in an 8m by 4m space in his backyard.[6] To put this yield in perspective the U.S corn industry, pushing nature to the limits with fossil energy subsidies (fertilizer) manages around 1kg per square meter.[7] Joel Malcolm is reporting roughly 3kg of fish and 6kg of vegetable.

In fact growing fish and vegetables together may be better for both than growing them separately, with benefits that go beyond simply canceling out the waste issue. Aquaponics practioners report lower incidences of disease in their fish and higher growth rates in their plants than would be expected in separate aquaculture and hydroponics systems.[8] More research is needed, but these early reports suggest a symbiotic relationship with great promise.

So why have you not heard of aquaponics before? Perhaps it's potential has languished, unexplored for the same reason as many other smart green solutions: the cheap and easy fossil fuel of the last few generations has made us lazy. Yet a chorus of voices grows ever louder, from climate scientists to oil geologists, that we need to smarten up. Fast.

I hadn’t heard the term until March when I arrived at the Maya Mountain Research Farm to study permaculture – a design system for sustainable living – full of the big questions and desperate for some answers (see my April 09 blog post). Permaculture is about applying ecological principles to human life, so that we can meet our needs without killing ourselves, and although aquaponics wasn’t on the syllabus it perfectly embodies this. One night MMRF’s director, Christopher Nesbitt, sat the group down in front of a laptop to watch ‘the aquaponics DVD’, a charming home production from Joel Malcolm [9]. Chris’s enthusiasm was palpable. This was ‘really cool’ he assured us, and through the shaky handycam walk arounds and strangely ‘oscar moment’ piano music, it became clear that it was. There was something to this.

The amateur roots of the system seem fascinating. There is some history of academic research in the field and a few businesses [10], but it appears that the driving force is now a global community of ‘hobbyists’. A few pioneers, notably Joel Malcolm in Australia (producer of the DVD), have experimented on a shoestring and shared their successes and failures with others around the world. That’s how Chris became hooked: “When I discovered the website I was up until sunrise” he told me. “What Joel Malcolm has achieved is fantastic". So Chris has been researching and preparing on and off for two years to build at demonstration system at his agroforestry farm and teaching center. I decided to return for my fourth visit to help out.

Designing the system
The elements of an aquaponics system are pretty simple: fish tank; fish; grow beds; gravel; plants; water; water pump; piping; roof. The final, crucial, component brings itself: the bacteria that convert fish poop into plant food in the water (ammonia to nitrites, nitrites to nitrates). Ongoing inputs are fish-food, top-up water and electricity for the pump.

Crucially we are building a system - every part affects every other. We have to think systematically, in the true sense of the word. The process is fascinating. Floor space affects grow-bed size, which affects tank volume, which affects the height from the ground of the grow beds, which affects height of fish tank to allow gravity feed etc. Systems thinking will be even more important once it is up and running, tweaking the elements until the ecology 'snaps' into place.

Chris had decided on a the ‘Constant Height In Fish Tank, Pump In Sump Tank’ model (CHIFT PIST !): water gravity-feeds from an overflow in the fish tank down through the grow-beds and then drains into a sump tank, from where it is pumped back at intervals to the fish tank, causing the process to start again. This is a version of the flood and drain system and it means that you do not need to be running the water pump constantly, as happens in a constant flow design. As our system will be relying on solar power keeping electricity requirements to a minimum is crucial. The CHIFT PIST arrangement also helps protects fish from an airy death - a fish tank pump would drain the system dry in the event of a leak - and the additional volume of water provided by the sump tank gives the system a greater tolerance.

When I arrived in late August a 25 foot by 25 foot area had been dug out down to the shale by MMRF staff James (right) and Herminio (above, drilling roof beams), long time employees responsible for many of the buildings on the farm and the real experts. It is impressive what these two achieve in a day. We smashed out nine holes and set concrete foundations for the sapodilla posts, which were bolted into place with threaded rod. Wood, on an agroforestry farm, is not in short supply and hurricanes happen, so triangulation is the name of the game at MMRF. There is a real elegance to the buildings here: chunky, charming and solid as sapodilla posts.

The roof is sloped following the two foot drop between the upper level (for the fish tank) and the lower lever (for the growbeds and sump tank). Roping up makeshift scaffolding we bolted on beams and rafters and triangulated them to the posts, then ‘pearlings’ between the rafters for attaching the roofing. There was a day in the blistering sun, painting the entire frame in burnt oil, blackening like derrick workers in a big strike - harvested from a local car mechanic workshop this will help preserve the structure from the munching of termites, carpenter ants etc and the dark, bronzed effect is fetching.

The fish tank will sit on a shallow concrete bed on the upper shale level and the sump tank directly on the shale. The grow beds need to be elevated for easy access and drainage. Using a rule of thumb calculation of 150 lbs per square foot (for stone masonry) we calculated that the grow beds will be carrying over 5000 lbs of gravel each, plus water - so if the ‘tables’ you can see in the photos (above and right) look built for One Tonne Man and his wife, that’s because its about that weight they will have to support.

Now we await delivery of our custom made tanks. Ordering them was fun, a day trip to Spanish Lookout. This Menonite town – Iowa with palm trees as Chris describes it – is Belize’s hub for agricultural supply and we were confident we could find what we needed. We looked at premolded plastic feeding troughs, and one at 600 gallons could have housed the fish, but in the end it was as cheap – and far more satisfying – to order bespoke tanks from Mr Penner, of Penner Metalworks Ltd. They will be sexy, shiney and crafted by hand.

So we are getting there. Three weeks into the project we are almost roofed and ready to wire and plumb. This will be the really fun part, piping the tanks together and installing the solar system.

In Part II: 'What are we gonna feed the fish?' and 'Did the Aztecs invent Acuaponics?'


THANK YOU to our supporters. Your donations are making this possible!

We are still fundraising! If you would like to help us finish the system email


[1] "Dr. Arnalds points out that between 1980 and 2000, the global population rose from 4.4 to 6.1 billion and food production increased 50 percent. With world population predicted to increase by another three billion by 2050, more food has to be produced within the next 50 years than during the last 10,000 years combined, he says."

[2] "Unsustainable Development 'Puts Humanity at Risk'," New Scientist online, October 17 2007.


[4] Intensive aquaculture (fish in tanks, as opposed to ‘fish farms’ in open water, which is known as extensive aquaculture) can use a huge volume of water. One paper provides a useful comparison: for three systems, each with a volume of 20,000 gallons, it quotes:
- 720,000 gallons per day for a trout raceway (constant water flow)
- 20,000 gallons per day for a semi-closed system
- 1000 gallons per day for a closed recirculating aquaculture system.

Another website, praising the environmental benefits of recirculating aquatic systems (RAS), provides figures for RAS systems that equate to 800 litres of water per kg of fish. I have not found comparable data for aquaponics, but the small systems seem be an order of magnitude more water efficient.

[5] "Because each plant in a hydroponics system is sharing the exact same nutrient, diseases and pests can easily affect each plant."

[6] Backyard Aquaponics Magazine, Issue 1, page 5, Joel Malcolm.

[7] In recent years US corn growers have pushed their average yield over 160 bushels per acre:

[8] Research by Dr Savidov (Brooks, Alberta, Canada) has indicated that once the ecology of an aquaponics system matures its productivity outstrips that of inorganic hydroponics. This reseach is cited in a submission to the Australian government where one of the authors states: "aquaponics, before it has fully developed its all-important microbiology to change fish wastes to plant food, is not as productive in greenhouse growing of food plants as inorganic hydroponics.
But when the aquaponic system is fully operational after six months, it leaps ahead of inorganic hydroponics. This leads to earlier maturity of greenhouse crops under aquaponics, and much heavier cropping."


[10] The history of aquaponics includes early work by the New Alchemy Institute, started in 1969, and an ongoing programme by the University of the Virgin Islands.

1 comment:

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