Feed formulation and manufacture
Table 7 shows examples of several feed formulations for Clarias gariepinus. Diets 4 and 9 are typical examples of farm-made feeds, while the other formulations are available either as pressed or extruded pellets. The South African formulations are least-cost feeds, and this is reflected in the protein content, which is 2–4 percent lower than the accepted requirement levels of 40–42 percent. Uys (1989) makes the observation that growth in C. gariepinus is optimized when fishmeal is included in the diet, even if the levels are less than 10 percent.
Specifically formulated commercial catfish feeds are only available in several African countries (Cameroon, Kenya, Nigeria, South Africa and Uganda). Extruded floating or slow-sinking pellets are only available in Nigeria and South Africa. Large-scale, intensive catfish farmers throughout the African subcontinent are currently (2010) still not satisfied with feed quality. No information could be obtained on the detailed composition of the commercially manufactured feeds.
As mentioned earlier, most farmers use farm-made feeds for economic reasons. Several farm-made feeds are produced, and these range from formulated dry mixes fed to the fish in punctured bags, to moist feed cakes or balls and dry pellets. Preparation and manufacturing technologies are simple – raw materials are milled and cooked (or pre-cooked, e.g. soybeans), mixed into a dough with water and extruded using a meat mincer. The “spaghetti’s” are sun dried or dried in locally manufactured driers and cut or crumbled into appropriate sizes. Anti-oxidants are expensive and not commonly used by small-scale feed manufacturers, such that storage of farm-made feeds is problematic. This is compounded by the absence of feed drying facilities. Farmers are advised to only mix and prepare quantities that can be used within a few days. Depending on feeding practices, FCRs of 1.1:1 have been reported for some farm-made feeds in Uganda and Kenya (Hecht, 2007).
Because of the high cost of vitamin and mineral premixes, farmers in Africa often use chicken layers mash, which contains minerals and vitamins, as a one of the primary components of catfish feeds. In fact, pig and poultry feeds are often used as alternate feeds for North African catfish throughout the African subcontinent (Liti, MacWere and Veverica, 2002; Nyandat, 2007; Ponzoni and Nguyen, 2008). Alternative sources of minerals used in Nigeria include bone meal and crushed periwinkle shells (Ayinla, 2007).
