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

Thesis (M.Sc.) - Asian Institute of Technology, 1989

Two herbivorous fish, grass carp (Ctenopharyngodon idella) and puntius (Puntius gonionotus) were compared in separate common polycultures of Nile tilapia (Oreochromis niloticus), common carp (Cyprinus carpio) and snakehead (Channa striata) over a period of 7 months. Stocking rates were 1 fish/m2 for grass carp, puntius and Nile tilapia, 0.25/m2 common carp and 0.05/m2 snakehead. There were two replicates for each treatment. All ponds were fertilized with buffalo manure, urea and triple superphosphate at the same rate. Feedstock was rice bran for first 2 months and chopped paragrass for the last 6 months of the experiment. After 7 months, the individual body weights of grass carp and puntius increased 337 g and 83 g, respectively. The mean daily weight gain of grass carp which was 1.60 g/fish/day is 4 times that of puntius, which was only 0.4 g/fish/day. The total net extrapolated yields of grass carp and puntius were 2205 and 1233 kg/ha/year respectively. Grass carp had an extremely low survival rate (38%> comparing to the survival rate of puntius which was 83%. The extrapolated net yield of fish from the polyculture of grass carp and puntius were 5,460 kg/ha/year and 3,941 kg/ha/year, respectively.