Optimization of stocking density and mixture ratio of tilapia and carp in rice-fish culture for higher bio-economic efficiency

Meeting the demand for carbohydrate and animal protein to feed the ever increasing population of Bangladesh is a huge challenge. Integrated rice-fish farming offers a unique solution to this problem. However, the productivity and profitability of rice-fish culture mostly depend on suitable fish species, mixture ratio in case of polyculture and stocking density among others. The study was, therefore, conducted to evaluate the effect of stocking density and mixture ratio on the productivity of rice cum Nile tilapia and Common carp fish culture. Fifteen different combinations of three stocking densities (8, 16 and 24 fingerlings 10 m(-2)) and five mixture ratios of nile tilapia and common carp (1:1, 1:0, 0:1, 1:2 and 2:1) along with rice sole culture were considered as experimental treatments arranged in a randomized complete block design with three replications. All the rice yield parameters (except thousand grain weight) were enhanced due to integration of fish which resulted in increased grain weight hill(-1). Stocking densities of 16 or 24 fingerlings 10 m(-2) irrespective of mixture ratio produced higher grain weight hill(-1) than 8 fingerlings 10 m(-2). But rice sole and rice-fish culture produced similar grain yield despite higher grain weight hill(-1) in rice-fish culture, because keeping ditches in rice-fish culture allowed lower no. of hills compared to rice sole culture. Both tilapia and carp showed highest growth rate and survival rate (%) at the lowest stocking density (8 fingerlings 10 m(-2)) irrespective of mixture ratio. But tilapia showed the highest productivity in monoculture (1:0) at the stocking densities of 24 or 16 fingerlings 10 m(-2) (764.1 and 687 kg ha(-1), respectively); carp on the other hand yielded the highest in monoculture (0:1) at the stocking densities of 8 or 16 fingerlings 10 m(-2) (828.7 and 747.9 kg ha(-1), respectively). Culture of tilapia and carp in 1:2 ratio @ 24 fingerlings 10 m(-2) with rice resulted in the highest total fish (tilapia+carp) yield (930 kg ha(-1)). All the rice-fish culture systems resulted in higher gross return and higher net return (except monoculture of carp @ 24 fingerlings 10 m(-2)) than rice sole culture. Only lowest stocking density irrespective of mixture ratio produced higher Benefit cost ratio (BCR) than rice sole culture. On the other hand, higher stocking densities resulted in lower BCR. Therefore, for higher productivity, mixed culture of tilapia and carp in 1:2 ratio @ 24 fingerlings 10 m(-2) can be integrated with rice, but from economic view point, monoculture of carp @ 24 fingerlings 10 m(-2) in rice field may be recommended.