5.1 Background
5.2 Research needs
5.3 Research approach
In many parts of Africa, small- and medium-size reservoirs built for irrigation or other purposes, have been used for an extensive type of fish culture, consisting of stocking and harvesting. In most cases, government or semi-government agencies do the stocking of finger-lings and it is left to the local populations to harvest as much of the production as they can, with available 'fishing gear. This has undoubtedly contributed in some degree to the availability of fish and the income of people in the neighbourhood, but the cost-effectiveness of this practice does not appear to have been properly studied. However, in recent years methods of utilizing open waters such as reservoirs, lagoons and rivers for controlled and more intensive fish culture, have been started in some countries.
Culture of fish in cages was attempted in Africa in Lake Victoria (Tanzania) and in Lake Kainji (Nigeria). Successful culture of Tilapia nilotica in cages was demonstrated in Lake Kossou (Ivory Coast) in recent years, with average production of up to 17 kg/m3 of cage per month, with stocking densities up to 70 kg/m3 and feeding with locally prepared diets. Commercial-size tilapia of 200-250 g weight could be produced in four to five months' time. Though the culture of all-male tilapia would be advantageous to increase the production, even unsegregated population would do well in cages, as breeding will be greatly reduced and even when breeding takes place, there is little likelihood of survival of fry in the cages. Besides T. nilotica, Clarias lazera also shows promise of being a suitable species for cage culture.
Locally fabricated cages have been used in the few places where cage culture has been attempted. However, a suitable cage design and economical cage-building materials have not yet been determined. Secondly, locally-produced feed, suited for use in floating cages, is not yet available. Thirdly, the economic viability of a commercial operation has not been demonstrated. The protection of cages in open waters presents a number of engineering and legal problems, which need to be solved for cage culture to become a widely accepted practice.
Culture of fish in pens has recently been initiated in the Ivory Coast in lagoons, using the catfish Chrysichthys as the main species, but this is, as yet, a local effort, and in very early stages of development to be included in the programme of work of the regional centre.
(i) Collection of data from selected African countries on the cost-effectiveness of stocking dams and reservoirs and their analysis to determine future research needs, if warranted;(ii) design of suitable cages and testing of cage construction materials for both standing and running water environments; design of rafts, floats, anchors and other requirements for installation of cages;
(iii) formulation, preparation and testing of feeds necessary for cage culture; development of suitable feeding procedures, including feed dispensers;
(iv) determination of stock density, feeding rates, growth and yield;
(v) monitoring of fish health and control of diseases, if they occur;
(vi) cage maintenance procedures;
(vii) economic evaluation of cage culture.
The collection of data on the results of dam and reservoirs stocking will have to be done from countries maintaining adequate records, mostly through questionnaires and correspondence. The analysis of data can be done at the Centre's headquarters, jointly by aquaculturists and an economist.
The Centre's headquarters is located by a river and so there should be no major difficulties in conducting experimental cage culture in a running water environment. However, there is no reservoir in the neighbourhood for experimental work to be done directly by the Centre staff. One of the large ponds of the freshwater fish farm to be established in Aluu can be used for preliminary studies, but more detailed studies will have to be done elsewhere, preferably in Lake Kainji, with the assistance of the research staff of the Kainji Lake Research Institute in New Bussa.
Different cage designs are already available, and based on these, test cages and auxiliary equipment should be fabricated locally, and tested in both standing and running waters. The need to reduce fouling, ease of operation, including regular cleaning and protection from poachers, should all be taken into account, besides cost in designing cage installations. Floating cages would appear to be the most suitable ones to be tried.
Effort should be made to prepare suitable feeds for Tilapia and Clarias which are selected for cage culture experiments. For cage culture, particularly culture in floating cages, it will be advantageous to have a floating feed. In feed milling, the high temperature extrusion process is employed for producing expanded floating pellets. This requires expensive and sophisticated equipment and a diet with a high percentage of cereal grains. The Dravo process of feed preparation, which is relatively less expensive (but more expensive than ordinary pellet milling) can be adapted for the production of low density pellets of high water stability, with some modification in feed formulation. The Dravo process, originally developed for the manufacture of breakfast food, should be modified, taking into account the differences in ingredient texture and flow characteristics in fish feed preparation. Simple and inexpensive mechanical driers also have to be developed for drying the moist product. Demand feeders should be tried for feed dispensation.
A series of cage production experiments should be conducted in both reservoir and riverine. environments, using factorial design as in other production experiments. In designing experiments, all significant factors including stock density, stocking size, feeds, feeding rate, method of feeding and growing period, should be incorporated. Environmental monitoring, as well as health inspection of the fish stock, should be undertaken regularly. The cost factor should be specially considered in each experiment, to determine economic viability.
Different measures for prevention of poaching should be tried with a view to recommending effective protection of stocks.
