Effects of dietary non-protein energy source levels on growth performance, body composition and lipid metabolism in herbivorous grass carp (Ctenopharyngodon idella Val.)

A study was conducted to determine the effects of dietary non-protein energy sources on growth, tissue lipid accumulation and lipid metabolism-related genes expression of grass carp. Triplicate groups of fish were fed for 9weeks on four isonitrogenous (300gkg(-1)) experimental diets with four levels of non-protein energy (6.52kJg(-1) control diet, 5.32kJg(-1) high-CEL diet, 8.46kJg(-1) high-CHO diet and 8.53kJg(-1) high-LIP diet respectively). Increasing dietary non-protein energy source levels did not improve the growth, and the high-CEL diet reduced the growth of grass carp. The high-CHO diet tended to induce high hepatosomatic index, with high fat and glycogen content of liver. However, the high-LIP diet caused the high mesenteric fat index, but did not increase liver fat. The mRNA abundance and activities of hepatic lipogenic enzymes were significantly increased in the high-CHO diet group, whereas the opposite tendencies were observed in the high-LIP diet group. Peroxisome proliferator-actived receptor- (PPAR) in liver and PPAR in mesenteric adipose tissue were up-regulated in the high-CEL diet group. Lipoprotein lipase (LPL) gene expression was significantly increased both in liver and mesenteric adipose tissue of fish fed the high-LIP diet, while the LPL gene expression was up-regulated in liver but down-regulated in mesenteric adipose tissue of fish fed the high-CEL diet. These findings suggest that an increase in dietary non-protein energy sources alters the genes expression of lipid metabolism and increased lipid deposition.