Effect of feed pellet buoyancy and stocking ratio of tilapia on fish and natural food in carp-tilapia polyculture ponds

Enhancing the growth of high value fish species in pond polyculture can benefit farmers economically, but tools to feed species in ponds differently are still not available. A factorial design with three types of pellet buoyancy (100 % floating pellets, 50 %–50 % mixture of floating and sinking pellets (on weight basis) and 100 % sinking pellets) and two stocking ratios of tilapia (SRT) ( equal (rohu:catla:silver carp:tilapia ratio = 1:1:1:1) and low (rohu:catla:silver carp:tilapia ratio = 3:3:3:1) were applied. Results show that pellet buoyancy influences fish biomass gain and survival (P < 0.01) by influencing inter- and intra-specific competition. Feeding a 50 %–50 % mixture of floating and sinking pellets proved to be the best strategy benefitting survival and biomass gain of all fish species. Fish performance was significantly less when feeding 100 % sinking pellets and intermediate at feeding 100 % floating pellets. A low stocking ratio of tilapia improved carp production but decreased total fish production (P < 0.05). Pellet buoyancy did not alter the natural food availability in the ponds while stocking ratio of tilapia negatively influenced plankton and benthos availability (P < 0.05). Thus a low stocking ratio of tilapia and feeding a 50 %–50 % mixture of floating and sinking pellets are the best strategies to enhance carp production in carp-tilapia polyculture ponds. Depending on farmers intention, tilapia production can be enhanced by increasing its stocking density and further by feeding a mix of floating and sinking pellets to carp-tilapia polyculture systems. • Mixing floating and sinking pellets can improve production in pond polyculture. • Stocking less tilapia enhances carp production in polyculture ponds. • Fewer tilapia in carp polyculture decrease production but not profitability. • Tilapia and natural food availability in ponds are negatively correlated. • Tilapia feeds more competently than carps on both pellets and natural foods.