Effects of stocking density on behavior and growth rate of European sea bass ( Dicentrarchus labrax) juveniles reared in a closed circulated system

Abstract

Four duplicated groups of sea bass juveniles (mean initial body wet weight 6.6±1.1 g and mean total length 8.56±0.52 cm) were reared under closed circulated water system conditions at different stocking densities (80, 165, 325 and 650 specimens/m 3) for 168 days. The aim of the experiment was to determine the general behavior and the effect of fish stocking density on fish growth, feeding and metabolism during the critical period of the first 6 months of the commercial life of sea bass. Statistically significant differences ( P<0.05) for final fish weight were observed between groups of the two highest and the lowest stocking densities. The highest specific growth rate and the lowest food conversion ratio were observed for fish of the highest stocking density. No statistically significant differences ( P<0.05) were found in haematocrit values, while no meaningful statistical differences were found in hepatosomatic indices in the groups of fish held at any stocking density. Significant differences in water quality among treatments was observed, with relatively poorer water quality occurring at the higher fish densities. The results suggest that schooling behavior of the sea bass may have been a factor in the observed differences in fish performance. However, no formation of clear dominance hierarchies was observed. It is concluded that sea bass, within the range of stocking densities tested and at least at its early stages, does not belong to that fish category which is characterised by an inverse correlation between stocking density and growth rate.