ABSTRACT

 The effects of biomanipulation and utilization of pond-grown cichlids for feed supplementation on feed quality, (flap/a and catfish growth and economic returns during semi-intensive catfish grow out in southeast Nigeria was studied. The experiment was divided into two treatments and designated Treatment 1 and 2 respectively. Treatment I was the traditional catfish-tilapia po/yculfure system whereby predation by catfish is relied upon as the only means of population control. This was the control experiment. Treatment 2 was catfish-tilapia polyculture under biomanipulation on operation whereby the cich/id component serves as an autochthonous fish protein source for supplementary feeding. In treatment 1, feeding was with a representative 12.6% protein content. In treatment 2, feeding in each pond was with feed in which fish paste prepared from all adult and 50% of sub adult Oreochromis nilot/cus removed 6-veek/y from that ponds displaced an equal weight of ingredients from the feed in Treatment 1. Exper mental unit was an earthen pond of size 9 m x 4 in (36 m2x 0.6 Tn at the outlet end and 0.8 m at the inlet end. The experiment was rplicated thrice. The ponds wet-c stocked with with 120 Heterobranchus long/f//is fingerlings of average weight 4.96 g (range 3.16-7.58 g) and 45 0. n/lot icus (24 adult and 21 sub adult) per treatment. Fish were fed at 3% fresh body weight day1(BWD) for 250 days. Fermented chicken - droppings (500 g) per pond were used in weekly basis for fertilization. Fish paste inclusion levels averaged 22. 7%, leading to significantly higher level of protein content (p < 0.001) and H. long/fit/s production in Treatment 2 (p < 0.01) but not 0. niloticus hiomass (p > 0.05), which become significantly higher in Treatment 2 only when the total weight removed was added to the final weight (p < 0.0001). 117 Treatment 1 cost: benefit was 1: 1.24 over variable cost and 1:0.93 over total cost. Cost: benefit in Treatment 2 was 1.2.59 over variable cost and 1:2.95 over total cost. It was concluded that feed qua7ity, fish production and economic returns were optimized through b/oman/pu/at/on operation. Treatment 2 is recommended for ado ption where high cos.t of fishm cal poses a constraint to aquaculture development.