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

Abstract

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.