Dietary protein and lipid levels affect the growth performance, intestinal digestive enzyme activities and related genes expression of juvenile small yellow croaker (Larimichthys polyactis)

The effects of different dietary protein and lipid levels on juvenile small yellow croaker (Larimichthys polyactis) was experimentally evaluated in 51 days study. Fish (initial weight 16.02 +/- 0.50 g) were fed with nine diets contained three levels of protein (430, 470, or 510 g kg(-1)) and three levels of lipids (60, 90, or 120 g kg(-1)) in triplicates. Specific growth rate (SGR) and weight gain (WG) of fish on 470 g kg(-1) protein and 120 g kg(-1) lipid diet were the highest. Protein efficiency ratio (PER) of fish on 120 g kg(-1) lipid diet was significantly higher than that of fish on other diets. Intestine lipase activity significantly increased as dietary lipid levels increased, whereas intestine protease activity showed the opposite trend. Relative expression of insulin-like growth factor-1 (IGF-1) and growth hormone receptor (GHR) significantly increased as dietary lipid levels increased. Relative expression of hepatic lipoprotein lipase (LPL) and fatty acid synthase (FAS) were enhanced considerably and decreased by dietary lipid, respectively. In conclusion, a diet containing 470 g kg(-1) protein with 120 g kg(-1) lipid (protein/energy (P/E) ratio of 24.55 mg protein kJ(-1)) was found to be optimum for juvenile L. polyactis, which could be a foundation for its nutrition research and large-scale cultivation.