Aquaculture ponds need careful planning.

Capital costs, running costs and potential market are the three major concerns faced by those who want to start fish farming, and I’ve often discussed these factors in relation to re-circulating aquaculture.

A group of 0,5ha ponds.
Photo: Nicolas James

I have made only passing reference to raising warm-water fish species in ponds, and would like to remedy this. Starting with the issue of potential markets, I have yet to find a producer of good quality tilapia who cannot sell his product – so long as he can supply regular quantities! There is a demand for both smaller fish of the wild-colour strain and larger-sized red tilapia. This means that pond-farming is most certainly economically viable, even in our generally temperate climate. In the warmer areas, water temperatures are suitable for fish growth for six to eight months of the year.

If your chosen market demands fish of 150g to 250g (small tilapia), then stocking with fry or fingerlings in September should result in a sustained harvest from March onwards. Later, you will also be able to harvest larger fish. Capital and running costs, meanwhile, bring us to the question of farm size. If ponds are fertilised with animal manure to increase primary productivity (and eliminate artificial feed costs), about 5t/ha per year can be expected. Thus, 1ha of water should theoretically earn a gross income of R150 000 per annum. This is the minimum viable economic size.

Remember, though, that a ‘hole in the ground’ approach will not work. Aquaculture ponds are in fact quite sophisticated structures, where depth, surface area, water quality, dyke construction, water inlet and outlet, catching basins and substratum are all important considerations. Ponds built on sandy soil that require constant pumping to keep full will never be viable. Those with crude means of filling and emptying will be a nightmare to operate commercially – and your fish will end up dying in the mud, rather than reaching the market in acceptable condition.

Pond construction, then, has several non-negotiables. These include: an accessible supply of adequate water; impermeable soil; correct slope; concrete or plastic water inlet and outlet devices; and a means of drainage by gravity. While first prize will always be gravity-filled ponds, many operate successfully on pumped water. The profusion of irrigation dams in South Africa sees ponds being constructed below these dams.

The slightly enriched water is then reticulated to the crops, with the added bonus of natural fertilisers in the form of nitrates already in the water. In areas that experience cold winters, a tunnel built over part of the pond will ensure warmer water in which the fish can over-winter.

Nicholas James is an ichthyologist and hatchery owner.