Effects of dietary non‐protein energy source levels on growth performance, body composition and lipid metabolism in herbivorous grass carp ( C tenopharyngodon 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 9 weeks on four isonitrogenous (300 g kg −1 ) experimental diets with four levels of non‐protein energy (6.52 kJ g −1 control diet, 5.32 kJ g −1 high‐ CEL diet, 8.46 kJ g −1 high‐ CHO diet and 8.53 kJ g −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 m RNA 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‐α ( PPAR α) in liver and PPAR γ 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.