ABSTRACT
This study investigates the performance of fish in ponds for the polishing of effluent from a waste stabilization pond system. Two pilot ponds, each of dimensions 2m x 4m x 1.25m were constructed, to receive the effluent from the maturation ponds of the Ahmadu Bello University waste stabilization pond system. The performance of the ponds in terms of the reduction in T5, 55, Chlorophyll-a, 800 and COO, were assessed when stocked with fish at rates of 5.0, 2.5, 1.25 and 0.0 fishes per m2. The ponds were operated at a detention time of 5 days throughout the study. The results show that fish population has significant influence on the performance of the ponds. Suspended solids removal as high as 85.6$ was observed for 5.0 fish/m2 stocking, while operation at 0 fish/m2 often resulted in effluent with increased S.S and chlorophyll-a concentration. A maximum COD removal of 40$ was obtained in the pond stocked with 2.5fish/m2 while 5C0D removal as high as 77$ was achieved in the pond with 5.0 fish/m2. The ponds were able to provide some BOO removal, though the ponds operated at 1.25 and 0.0 fish/m2 indicated increases in BOO of up to 11.5$ and 10.7$, respectively. One of the full-scale maturation, ponds feeding the pilot ponds, iuas also used to investigate the rate of growth and productivity of 300 fishes. Average fish growth rate of 0.83g/d. or 0.14g/m2.d were observed over a period of 6 months of investigation. Bacteriological tests on the guts and flesh of the fishes indicated the presence of coliform bacteria, but absence of sulphite-reducing bacteria.