Closed heated systems for tilapia

Our much-beloved Mozambique tilapia requires water temperatures of 26°C or higher to grow rapidly. There are several ways to achieve this under culture conditions, but not all are practical.

Closed heated systems for tilapia
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Most strains of the Mozambique tilapia (Oreochromis mossambicus), or blue kurper, only grow at a commercially acceptable rate at water temperatures of 26°C or higher, with the optimum being 28° to 32°C. This is really warm water, so how can it be achieved under culture conditions? Winter water temperatures throughout South Africa are low, due to both latitude or altitude, and even in the warmest parts of the country, ponds would be at optimum temperatures for growth for only four months annually.

This is one of the main reasons tilapia culture has yet to succeed here: it requires a closed, heated system. Such a system is self-contained and typically intensive, with large numbers of fish occupying small volumes of water – very different from the highly productive but extensive pond-culture in Asia. The most cost-effective method of heating water is to use greenhouse tunnels. A well-insulated greenhouse can raise water temperature by 6°C to 8°C over the ambient temperature.

This represents a significant amount of free energy in a 240 000l system. To heat this using an electric heat pump would require a 70KW unit, consuming about R380 of electricity per day. Other options include coal- or wood-fired boilers. As heating is required mostly at night, an automatic stoker is essential. With coal, this is possible using an auger drive that feeds the coal from a hopper to the furnace. With wood, unless chips are used, automatic stoking is not an option.

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Paraffin heaters have two drawbacks: they consume a good deal of expensive fuel, and may leave a film on the water surface. Since this hampers oxygen transfer to the water, these heaters are considered unsafe for indoor fish culture.
Although an attractive and clean form of free energy, solar heating also has two disadvantages: it is costly to install and functions only in daylight. A total of 69 domestic-type solar heaters would be required to warm a 240 000l system. At about R7 000 per panel, this represents a heavy capital outlay.

Indoor systems in heated, insulated buildings are used with success overseas. Tilapia are even grown in thermally protected warehouses in northern Germany – and Siberia, of all places! One consideration that is often overlooked, however, is the benefit to fishes’ health of growing ‘outdoors’, in natural sunlight. Experience has shown fish reared in tunnels are healthier and of a better quality than those from entirely indoor systems.

The combination of free heat from the greenhouse, coupled with the health benefits to the stock, make tunnel culture a winner, I believe. Two final words on tunnels: transparent sheeting is more effective in terms of heat build-up inside than light-diffused plastic (South African tunnel-plastic suppliers please note!), and the ‘black plastic piping on the roof’ concept simply does not work commercially. The heat transfer is far too slow in large water volumes.

Nicholas James is an ichthyologist and hatchery owner. Email him at [email protected]. Please state ‘Aquaculture’ in the subject line.