Effects of dietary lipid levels on growth performance, feed utilization and fatty acid composition of juvenile Japanese seabass (Lateolabrax japonicus) reared in seawater

Triplicate groups of 40 Japanese seabass Lateolabrax japonicus (initial weight, 11.3 +/- 0.4 g) reared in seawater (salinity, 30.0-33.0 g L-1) were fed with five isonitrogenous (41.3 +/- 0.2% crude protein) and isoenergetic (18.5 +/- 0.3 MJ kg(-1)) experimental diets formulated with increasing lipid levels (4.3, 8.4, 12.2, 15.8 and 20.1% lipid) for 10 weeks. Survival throughout the feeding experiment ranged from 87.5 to 100%, but the survival of fingerlings fed with the 4.3% lipid diet was significantly lower than the rest of the diets. At the end of the feeding experiment, fish fed with 12.2% lipid diet showed optimal growth performance (P < 0.05). Lipid contents of whole body, liver and muscle increased in parallel with the increase in dietary lipid levels. Viscerosomatic index (VSI), hepatosomatic index (HSI) and muscle lipid content were higher in 20.1% lipid group than those in the rest of the lipid level groups indicating that viscera and muscle tissues played important contributions to body lipid deposition. High proportions of 18:1n-9, eicosapentaenoic acid (20:5n-3; EPA) and docosahexaenoic acid (22:6n-3; DHA), and low concentrations of n-6 polyunsaturated fatty acids (PUFAs) occurring in liver and muscle, to some extent, reflected fatty acid (FAs) composition in the experimental diets.