Effect of pellet-size on fish growth, feeding behaviour and natural food web in pond polyculture

In carp-tilapia pond polyculture, carps are stocked once and usually harvested each 12 to 24 months, while, tilapia is stocked and harvested each 4 to 6 months. Therefore, per carp cycle there are 3 to 6 tilapia cycles. With time, carps grow bigger while tilapia reach only 10 to 50% the mass of carps. Pellet size can offer a feeding management tool in the ponds with large carp and small tilapia. This experiment investigated whether pellet-size can steer the growth of large carps (∼ 500 g) and small tilapias (∼30 g) in polyculture ponds. Four pellet-size treatments were applied in this study, each with a different combination of small (2 mm) and large (6 mm) pellets (on weight basis): S100L0 (100% small, 0% large), S50L50 (50% small, 50% large), S25L75 (25% small, 75% large) and S0L100 (0% small, 100% large). Each treatment was applied to six replicate ponds. The experiment lasted for 8 weeks. The treatments did not alter carp production, but tilapia production was highest in S100L0 treatment ponds (P 0.05) except phytoplankton diversity which was positively influenced when feeding more large pellets. The plankton population increased with the progression of the experiment, suggesting the food web was not fully exploited. In conclusion, pellet-size proves to be a feeding management tool to steer the production of tilapia as well as of total fish biomass, but not of carp's biomass in carp-tilapia pond polyculture.