A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science, School of Environment, Resources and Development

Thesis (M.Sc.) - Asian Institute of Technology, 1997

An experiment was conducted for 112 days to evaluate the growth performance of hybrid catfish and carps (silver carp, rohu and mrigal) in three different stocking ratios of 3.2:1, 4.8:1 and 6.4:1, and their impact on water quality and nutrient budget. Hybrid catfish were stocked in 1.2 m3 cage, at a density of 100, 150 and 200 fish/cage. Fish were fed on pellet feed, at a rate of 2% body weight. Carps were stocked at a rate of 5,000 fish/ha in 250 m2 ponds. The ratio of carps was 1: 1 : 1. The carps were grown solely on natural food produced by nutrients wastes from caged catfish. Ponds were fertilized prior to stocking at a rate of 4 kg N/ha/day and 1 kg P/ha/day. Net fish yield of hybrid catfish (28.7 kg/cage), net yield of carps (13.3 kg/pond) and combined net yield of caged catfish and pond carps (127.9 kg/pond) were significantly higher (P<0.05) in higher stocking density of catfish. Stocking ratio of 6.4: 1 appeared to be the best stocking ratio. Stocking ratio did not affect water quality. Hybrid catfish culture released 61-64% N and 76-79% P, out of which carps recovered 3.1-3.8% N and 2.4-2.9% P, and 1.5-2.3% N and 1.3- 14.0% P were lost to the water column. Rest nutrients were unaccounted for. Nutrients derived from the wastes equal to fertilization rate of 0.9-1.6 kg N/ha/day and 0.3-0.5 kg P/ha/day, which were grossly inadequate for phytoplankton production to support the growth of herbivorous carps.