Y. Staykov*, S. Stoyanova
Department of Biology and Aquaculture, Faculty of Agriculture, Trakia University, Stara Zagora, Bulgaria

Abstract. The stocking density is one of the most important parameters of fish growth and productivity in farming activities. The aim of the study was to evaluate the effects of different stocking densities on growth rate and body indices of common carp fingerlings /Cyprinus caprio L./, reared in net cages. The trial was set up as a complete randomized design, with three different stocking densities (SD1 – 300, SD2 – 500 and SD3 – 700 fish/m3), each of them with three replications. The initial body weight of fish was 0.9 g. The size of net cages was 1.50 х 1.50 х 1.50 m, with effective depth of the mesh 1.0 m and water volume – 2.25 m3. The trial lasted 122 days. The highest final body weight was attained by fish with stocking density of 300 fish/m3 – 75.55 g. The increased stocking density resulted in lower final weight of fingerlings SD2 and SD3 (p<0.05, p<0.001). The higher stocking density influences substantially the exterior traits and body indices of carp fingerlings. There were statistically significant differences between mean relative body width between SD1 and SD3 groups (р≤0.001) as well as between relative head length group between one summer old fish from SD1 and SD3 (р≤0.001). The survival of fingerlings decreased as the stocking density increased, but remained within the allowed reference ranges for all three experimental variants. The fish production was the highest for carp fingerlings stocked at SD3, but it was also associated with a large proportion of fingerlings whose size was under the fish farming standards.