A partial economic analysis for Nile tilapia Oreochromis niloticus L. and sharptoothed catfish Clarias gariepinus (Burchell 1822) polyculture in central Kenya

Aquaculture development in Kenya has been hampered by lack of targeted feeds. Chemical fertilizers can enhance natural food production and thus indirectly provide protein to complement energy-rich cereal brans used as feed. Consequently, an experiment was conducted at Sagana Fish Farm in central Kenya to realize least-cost combinations of rice bran and fertilizer. Twelve 800 m2 (0.08 ha) ponds were stocked with juvenile (32 g) Oreochromis niloticus L. at 2 m−2 and Clarias gariepinus (Burchell 1822) (fingerlings of 4.6 g) at 0.2 m−2. Four treatments, calculated to approximate isonitrogenous conditions, were applied in triplicate as follows: (1) urea and diammonium phosphate (DAP) to provide 16 kg of N ha−1 week−1 and 4 kg of P ha−1 week−1; (2) urea and DAP applied to give 8 kg of N ha−1 week−1 and 2 kg of P ha−1 week−1, plus rice bran fed at 60 kg ha−1 day−1; (3) rice bran fed at 120 kg ha−1 day−1; (4) rice bran as in treatment 3 and fertilizer as in treatment 2. Ponds were sampled monthly to measure fish growth, and drained completely after 20 weeks. A partial economic analysis indicated minimal net profits of K.Sh. 18 851 (US$ 251), K.Sh. 9895 (US$ 132), K.Sh. 3299 (US$ 44) and K.Sh. 7015 (US$ 94) for treatments 1–4, respectively, because of high feed and seed costs.