By Keith Nicholson
Fish farming has been practiced for thousands of years. In Africa, several countries to the north of Zimbabwe have been farming fish for 50-60 years. In Zimbabwe, a few commercial farms were started in the early 1980s. Very few of these continued for more than a few years. Lake Harvest is Zimbabwe’s largest commercial fish farm, producing 6000 tons per year from cages in Lake Kariba. If we take Lake Harvest out of the equation, farmed fish production is very likely to be less than 1000kg per annum at this time. There are some exciting projects that have started and tonnages are likely to increase quite dramatically in the coming years. In 2016, Africa produced 1,177,435 metric tons of farmed fish.
The main producing countries are Egypt (largest by far with 940 000 tons), followed by Uganda, Nigeria, Ghana, Zambia, Kenya, and Zimbabwe – which makes the list thanks to Lake Harvest. Tilapia (bream) is relatively easy to cultivate. They are resistant to poor water quality and diseases and are able to efficiently convert many organic animal and agricultural waste materials into high quality protein. However, having stated that the above, best growth rates are only going to be achieved if water quality is good and the fish are fed a well-balanced high protein diet. If you are interested in farming fish, you will need to decide on what level of farming you wish to do and the method of raising the fish you will use. Fish farming can be done at subsistence, intensive or super intensive levels. Methods of farming can be in existing dams, simply gill netting, constructing ponds, or using cages in dams or in tanks.
Tilapia require warm water to grow. With the exception of the Eastern Highlands in Manicaland, all other provinces are warm enough in the summer months. Work on producing fish for seven to eight months of the year. Even at Lake Kariba, in June and July, it cools sufficiently to slow down growth quite dramatically. A farmer needs to plan his/her stocking program with winter months in mind. It is perfectly possible overwinter fish of any size. Pond farming is the most common system for raising fish. It is the least expensive to establish, carries the least risk and is flexible in terms of feed input. Cages are more expensive to build and maintain, require a high level of management and the fish are totally dependent on the quality of the feed fed to them. Tanks are also fairly expensive to construct. There are plastic on metal frame tanks available which are cheaper than building a concrete tank. Tanks require running water 24/7 and the quality of the water must be kept within certain parameters in order for the fish to grow well.
In some areas, there are opportunities to divert water from a stream of irrigation canal and flow the water through tanks. This through-flow system would prove ideal conditions for fish. As with rearing fish in cages, fish grown in tanks are totally dependent on a high protein pelleted feed. Expected yields There are many parameters that will determine the rate of growth, such as water quality, type of feed, stocking density, oxygen levels, temperature
and others. In ponds, one can expect to harvest 500 grams to one kilogram of fish per m2. Higher yields will require aeration and daily water replacement of five to 20% of total volume. In cages and tanks, we work on cubic metres and one can expect 15-60kg/m3. Feed, electricity for pumping water and labour costs are going to be the main overheads. Feed costs (soya bean price has been pegged at $780/ton to Grain Marketing Board) make or break the
project. Integrating your fish farm with other farming activities may well be the answer to profitability.