Differential regulatory effects of dietary lipid level on growth, antioxidant capacity and expression of genes involved in lipid and glucose metabolism of juvenile mud crab Scylla paramamosain

Three isonitrogenous diets (41% crude protein) with 4.87%, 10.75% and 16.10% lipid were designed to evaluate the effects of dietary lipid levels growth, antioxidant capacity, expression levels of genes related to lipid and glucose metabolism of juvenile Scylla paramamosain. Each diet was fed to four replicates of 32 crabs with initial weight 5.10 +/- 0.05 g for 6 weeks. The results indicated that crabs fed diet with 10.75% lipid exhibited signif-icantly higher percent weight gain (PWG) and specific growth rate (SGR) than those fed diet with 4.87% lipid (P < 0.05), and crabs fed diets with 10.75% and 16.10% lipid had significantly higher protein efficiency ratio (PER) and feed efficiency (FE) than those fed diet with 4.87% lipid (P < 0.05). Crabs fed diet with 4.87% lipid had the lowest concentrations of lipid and glycogen in muscle, lipid content in hepatopancreas and hemolymph glucose among all treatments (P < 0.05). The concentrations of free fatty acid (FFA), triglyceride (TG), total cholesterol (TCHO) and pyruvate in hemolymph and hepatopancreas increased significantly with the dietary lipid levels increasing from 4.87% to 16.10% (P < 0.05), while the concentration of crustacean insulin-like (INS) in he-molymph and crustacean hyperglycemic hormone (CHH) in hepatopancreas significantly decreased with the increase of dietary lipid levels (P < 0.05). In the hepatopancreas, The Oil Red-positive area significantly increased with increase of dietary lipid levels (P < 0.05). Crabs fed diet with 16.10% lipid showed the lowest concentration of glutathione peroxidase (GSH-Px) (P < 0.05). On the contrary, the highest concentration of malondialdehyde (MDA) was observed at crabs fed diet with 16.10% lipid (P < 0.05). Crabs fed diets with 10.75% and 16.10% lipid down-regulated expression of genes related to long-chain-PUFA biosynthesis and lipid synthesis in hepatopancreas than those fed diet with 4.87% lipid (P < 0.05). The mRNA level of cpt1 significantly up-regulated with the increase of dietary lipid levels, while the mRNA expression level cpt2, acox1 and fabp4 in hepatopancreas significantly down-regulated in crabs fed diets with 10.75% and 16.10% lipid (P < 0.05). The expression of gk and pfk in crabs fed diet with 16.10% lipid significantly down-regulated than those in other groups (P < 0.05). The expressions level of genes related to gluconeogenesis significantly down-regulated in crabs fed diets with 10.75% and 16.10% lipid (P < 0.05). The lowest mRNA expression of glucose transporter 4 (glut4) was occurred in crabs fed diet with 16.10% lipid (P < 0.05). Overall, the results of present study demonstrated that the dietary 10.75% lipid can improve the growth and feed utilization for juvenile mud crab, in addition, dietary lipid can affect the antioxidant capacity, lipid metabolism, glucose metabolism and insulin signaling pathway, dietary excessive lipid resulted in lipid deposition of hepatopancreas for juvenile mud crab.