If the achievements of other countries can be emulated in Africa, our water resources pose a partial solution to feeding the increasing population in the future when pressure will be placed on our wildlife resources.
According to F.A.O. estimates, Asian nations lead the way in fin-fish production. China alone produces 760 000 tonnes of fish from aqua-farms. In relation to many more fish-conscious nations, our fish production is low, falling far short of requirements. We should aim at a target of an annual consumption of 10kg of wet fish per person. Viewed in this light, our present production of fish is obviously inadequate and a maximum utilisation of our water resources is necessary to achieve these targets.
The projected development of dams necessary to keep pace with economic growth and to satisfy water demands shows that storage capacity will have to increase considerably. Thus fish production from large dams need not be static if the many new dams coming into existence are used for fish production. Much greater use of our dams should be encouraged and fishing policy must be dictated by the size of the dam. A 400ha dam for example would be more suited to a small-scale fisherman whose requirements are satisfied by an annual yield of 4 tons than being subjected to the netting pressure of a more sophisticated operator looking for a big return on catches.
Despite the potential offered by large dams for increasing fish production, they obviously have their limitations and reliance cannot be solely on them to approach the targets mentioned earlier. Other ways must therefore be examined.
An analysis of the fish production potential of small farm dams showed privately owned and small government built dams can contribute significantly to the total fish production. There is a necessity to investigate the situation in individual countries and determine the level of productivity of the smaller dams and determine more exactly the area of water available. Some dams for example, might dry up before the rains. Such an investigation could obtain information which would allow actual production to be compared with possible production and thus determine the level of extension work required to maximise the use of small dams for fish production.
Three types of fish culture may be considered, namely:
- Rural subsistence type;
- Semi-intensive; and
Small ponds scattered throughout the rural areas and stocked with suitable species offer a means of providing villagers with a daily ration of protein-rich food; weirs or barrage dams can considerably increase the carrying capacity of streams, while large shallow scrapes in marshy areas provide similarly suitable habitats for fish. Concrete reservoirs built for water storage should be stocked.
Semi-intensive and intensive fish culture is usually profit-orientated, and usually involves pond production. Semi-intensive involves moderate stocking of fish ponds to produce yields of 1 – 3 tonnes per ha per annum.
This type of operation can be profitably combined with any form of livestock operation, where quantities of fish are essentially imposed by the oxygen levels in the water, which can result in the mass mortality of the fish by over-manuring and over-stocking.
Intensive operations involve a very much higher stocking rate in production ponds, made possible by aerating the water, or by having a flow of oxygenated water and the intensive feeding of the fish. A combination of fish species are used and yields of up to 25 tons per hectare can be obtained. For example, it has been reported that the production level of 6 tonnes of carp in 0.37ha (16 tonnes/ha) in a year, in a pond, with a flow-through of water, receiving high energy pig waste, has been achieved. Intensive fish farming therefore requires a more sophisticated management technique and is more costly.
However, pond culture is not the only means of culturing fish. Other possibilities are; cultivating fish in cages, raceways, tanks, in sewage effluent or the heated water from power stations or thermal springs. Cage culture is becoming increasingly popular in some areas, notably the Philippines and to a certain degree in West Africa. In the United States production of over 5 tonnes per hectare has been obtained for catfish, and in Japan production as high as 280 tonnes per hectare has been obtained for marine fish. In the Netherlands, yields have been obtained of over 100 kg/cubic metre of fed grass-carp in cages. In South Africa the species Sarotherodon mossambicus is reported to have gained 140-170g in .87 days in sewage effluent.
Fish have potentially better food conversion efficiency than terrestrial animals and their mass gain per amount of food eaten is higher than any other type of livestock. They are efficient converters of either natural or artificial foods into edible quality protein.