Effect of Initial Size on Growth Rate of Rainbow Trout, Oncorhynchus mykiss, Reared in Cages on the Turkish Black Sea Coast

A rearing trial was carried out to examine the effect of initial fish size on growth rate of rainbow trout, Oncorhynchus mykiss, reared in marine cages. The fish were introduced into the cages at the same stocking density (2.1 kg/m3) and three different size groups (small: 52.1±10.8 g, n=2,250; medium: 77.6±11.7 g, n=1,500; large: 118.6±20.1 g, n=1,000) with two replicates. The fish were fed to satiation three times a day with commercial pelleted diet. The growth, feed conversion, daily feeding and final biomass were found to be significantly affected by stocking size (P<0.05). The specific growth rate in small group (1.11%) was better than other two groups (1.02%). The highest daily feeding rate was in large (1.66%), and followed by medium (1.55%) and small size groups. The feed conversion values varied between 1.37 and 1.70. There was a negative relationship between the final biomass and initial stocking size of fish. Growth performance of rainbow trout appeared to be depressed at large size group.