Effect of population strategies on production of polyculture system

Abstract

Rearing trials were conducted in four 0·17 ha earthen ponds, with an average depth of 1 m, at Fish Culture Research Institute, Szarvas, Hungary, to examine the effect of various stocking strategies on production and economic potential. The strategies tested consisted of stocking: Common carp (95%), Grass carp (4%), Catfish (1%) only; Common carp (70%), Grass carp (4%), Catfish (1%) plus Bighead carp (25%); Common carp (70%), Grass carp (4%), Catfish (1%), and Silver carp (25%); Common carp (70%), Silver carp (17·5%), Bighead carp (7·5%), Grass carp (4%) and Catfish (1%). The comparisons were tested at the same densities (20 000 fish/ha pond). Fish were fed a prepared ration twice daily and seine-sampled at 4-week intervals throughout the 102 days rearing period. Ponds were harvested by complete drainage at the end of the growing period. Growth and survival rates were different. The stocking of Common carp at high level (95%) with Grass carp (4%) and Catfish (1%) without Silver carp and Bighead carp resulted in low production level — nearly half — as compared to stocking Common carp (70%), Silver carp (17·5%), Bighead carp (7·5%), Grass carp (4%) and Catfish (1%). Also, survival was more variable; it was 63% in the first stocking structure (pond No. 1), while it was 73% in the second structure (pond No. 4). Mean size of fish species was higher in the second stocking structure than all the three structures. Preliminary economic feasibility analyses of the various strategies were performed for situations where ponds and associated facilities were already available. Our data suggest that stocking strategy which consists of stocking Common carp, Silver carp, Bighead carp, Grass carp, and Catfish result in a greater net revenue.