Effect of dietary protein and lipid levels on growth and body composition of juvenile turbot (Scophthalmus maximus L) reared under optimum salinity and temperature conditions

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Abstract
Effect of dietary protein and lipid levels on growth and body composition of juvenile turbot was determined at optimum salinity and temperature conditions of 17 g L−1 and 19.2 °C, respectively, by using 3 × 2 (protein levels: 550, 600 and 650 g kg−1; lipid levels: 69 and 168 g kg−1) factorial design with three replications of each. Fish were hand-fed to satiety twice daily throughout the feeding trial. Weight gain and specific growth rate of fish were significantly (P < 0.05) increased with increased dietary lipid level, but not by dietary protein level. Daily feed intake was significantly (P < 0.05) affected by both dietary protein and lipid levels. Feed efficiency ratio and protein efficiency ratio were significantly (P < 0.05) affected by dietary lipid level, but not by dietary protein level. Moisture content of whole body was significantly (P < 0.05) affected by dietary lipid level, but not by dietary protein level. Crude lipid content of whole body was significantly (P < 0.05) affected by dietary lipid level, but not by dietary protein level. Significantly higher 20:5n−3, 22:6n−3 and n−3 highly unsaturated fatty acids were observed in turbot fed the low lipid diet than fish fed the high lipid diet in all protein levels, but significantly lower 18:2n−6 was observed in fish fed the former compared with the latter. In considering results of growth, specific growth rate and efficiency of feed, optimum dietary protein and lipid levels for juvenile turbot seemed to be 550 and 168 g kg−1 of the diet, respectively, under optimum salinity and temperature conditions.