Sunday, October 18, 2009

Future Fish´n´Chips (Part II)

Roof... Tanks... and Black Soldier Fly Action

The splashing sound was different from the regular river noise. Then round the bend the dory appeared, almost eclipsed by the fish tank: successful delivery number one by James and Herminio.

This was the final leg of the fish tank’s journey from Mr Penner’s metal workshop to its new home in the aquaponics system at MMRF. Chris and I had earlier collected three of the six tanks from Spanish Lookout and, firmly strapped to the truck, driven them back to Toledo district. Now, delivered up river, the fish tank was hauled up the bank and set on its level concrete foundation.

There it sat under the newly fitted roof. That hadn’t fitted. Ordering roofing from a hardware store whose menu included only a handful of options, one could be forgiven for making some assumptions. Such as, that the ridges of the transparent and metal versions would correspond. Nope. We had to engineer a one inch rise so that the upper metal panels would ‘sit’ on the lower plastic ones. In the end it looked fine but it taught me a useful lesson: never assume, always check.

The 3.5 foot high by 6 foot diameter fish tank will hold around 700 gallons (US) of water. Using spare 1 ¼ inch piping available on the farm, plus newly bought connectors, we donned our Mario Brothers outfits and started plumbing. From the fish tank the piping splits at a t-junction and drops to the end of each pair of grow beds where it splits again. Ball valves will provide flow control – balancing water input between the four beds – and piping with holes drilled on the underside will run back down the length of the beds, flush with their edges. The water will drain out of these holes, fill up the bed to the level of the stand pipe (which allows excess to drain off) and then drain out downhill to the sump tank.

My time at MMF is up. I leave a fine looking system that is two thirds complete. It awaits installation of a solar panel with water pump, to feed water back up to the fish tank. There is also the gravel for the grow beds to be collected from the river. This is a significant task as each grow bed requires around 35 rice-sacks worth, which must first be carefully sifted for correctly sized stones and then hauled uphill by hand. Chris hopes to add a final touch of class to the site with stone paving and a seating area, where visitors can sit and watch the fish while learning the basics of aquaponics.

Then just add water! And fish! The plan is to source these from the river, which will be the crucial first test in this experimental system: Will local fish species survive in a tank? What size will they reach? What stocking density will they tolerate? And what will they eat?

What will the fish eat?
This was my big question on learning about aquaponics. Yes I was excited about fast-growing vegetables and garden-sourced fish but, I reasoned, if you need to buy synthetically produced, fossil fuel subsidized fish food every month from the specialized pet store… not the sustainable dream.

The answer may lie in Black Soldier Fly (BSF). Whilst researching online I came across a number of references to BSF composting and use as fish food. With ‘nature’s most efficient stomach’ the larvae can chomp through 15kg of restaurant food waste per square meter per day [1]. Most exciting of all they can be self-harvesting: once mature, the larvae wriggle out of the compost to find a dry spot in which to pupate. With a specially designed compost bin they can be, in theory, collected neatly in a pot.

This seems to offer a perfect solution for converting waste organic matter, of which there is plenty, into dense, nutritious fish food.

‘How do we get some?’ was the next question. My reading told me they are extant throughout tropical, subtropical and temperate regions so I built a test composter bucket and waited. But in one of those wonderful examples of practical wisdom, we discovered that Chris was already harvesting BLF larvae for his chickens. His ‘maggot bins’ were pulsating with them and, just as stated online, when he tipped out the contents the chickens went crazy for them. The final step was simply to design a self-harvesting composter.

My first attempt, based on a useful example online, has not proved prolific. The barrel is teaming but they’re not exciting en mass. We are hoping that a second tilted barrel design will offer a less intrepid and more convenient route.

If this works Chris may have a fantastic and free source of fish food. Other potential sources include pelletised Meringa Oleifera, a protein-rich plant easily cultivated on the farm, and perhaps a solar powered bug zapper hung over the fish tank! Together these sources may offer a balanced diet sufficient for the fish. If so all three of the major ongoing inputs of the system – electricity, water and fish food – could be sourced sustainably.

This project is an experiment to see if the ‘backyard aquaponics’ systems that initially fired Chris’s interest can be adapted to rural, off-grid Belize. If the system at MMRF proves itself a highly productive source of fish and vegetables, a second question arises: could similar systems, manufactured out of cheap materials, provide an attractive option for local farmers and village co-operatives?

Aztec Aquaculture
One indication that the answer could be ‘yes’ is the fact that symbiotic aquaculture and agriculture is by no means new to Central America. In fact it may even have been invented here. There is an ancient agricultural method known as ‘chinampas’ in which vegetables are grown in raised beds surrounded by canals, whose nutritious sludge is dragged up as fertilizer. The Aztec capital of Tenochtitlan, (now the site of Mexico City) was famously built in a shallow lake and used this method of production, perhaps providing the foundation of its high population density, wealth and therefore dominant regional power. In fact there are antique chinampas fields at Pulltrouser Swamp in northern Belize.

Some agricultural entrepreneurs have started to reintroduce this method, often utilizing the fast growing Water Hyacinth for mulch [2] and in time it may undergo a renaissance. Will its smaller infrastructure requirements make chinampas a more realistic option for large-scale adoption than aquaponics?

What is very likely, at least, as future fish and fossil fuel stocks dwindle, is that some version of mixed aquaculture and agriculture will have a critical role to play in Belize as in the wider world. We hope that the demonstration aquaponics system at MMRF will be a fertile first step.


THANK YOU to all those who have supported this project through your generous donations.

To follow further progress on this project visit


[1] This is reported by ESR International, a green technology company focused on the elimination of landfill. See They went on to develop and market the BioPod, a BSF composting bin whose design seems to have inspired a number of DIY attempts recorded online, along with my own. (


No comments:

Post a Comment

Leave a comment. Makes me happy.