Effects of Dietary Carbohydrate Types on Growth Performance and Glycolipid Metabolism of Juvenile Turbot (Scophthalmus maximus L.)

In order to study the effects of dietary carbohydrate types on the growth, digestion and energy metabolism of turbot (Scophthalmus maximus L.), four kinds of isonitrogenous and isoenergetic diets containing different carbohydrates (glucose, sucrose, β-glucan, starch) were designed. Juvenile turbot weighing (7.03±0.15)g were selected for an 8-week culture experiment with the growth performance, apparent digestibility, general composition, body shape, liver tissue morphology, serum biochemistry, glycogen content, glucose metabolism, lipid metabolism and energy metabolism of turbot measured. The results showed that the specific growth rate, weight gain rate and protein efficiency of starch group were significantly higher than those of sucrose group and glucose group (P < 0.05), and the feed coefficient of glucose group was the highest and significant in comparison with other three groups (P < 0.05). Compared with glucose group and sucrose group, the apparent digestibility of dry matter and protein in starch group and dextran group were significantly improved (P < 0.05). Compared with other three groups, the area of lipid droplets in liver slices in glucose group was significantly increased (P < 0.05). Compared with other groups, the contents of serum triglyceride, glucose, total cholesterol and liver glycogen in glucose group were much higher (P < 0.05) while that of muscle glycogen in sucrose group was much lower (P < 0.05). The relative expression levels of glucokinase, pyruvate kinase and phosphofructokinase genes in the sucrose group were significantly higher than those in other three groups (P < 0.05) while those of 1, 6-diphosphate fructase and 6-phosphoglucose kinase genes in glucose group were significantly lower (P < 0.05). The relative expression levels of fatty acid synthase, sterol regulatory element binding protein 1 and acyl coA oxidase genes in glucose group and sucrose group were significantly lower than those in dextran group and starch group (P < 0.05). The relative expression levels of citrate synthase, isocitrate dehydrogenase 1 and dihydrolipoamide succinyltransferase genes in dextran group and starch group were significantly higher than those in glucose group and sucrose group (P < 0.05). The results showed that, compared with simple carbohydrates such as glucose and sucrose, turbot juveniles were more sensitive to starch β-carbohydrates with complex structures such as dextran which have stronger utilization ability. Under the experimental conditions, starch was the most suitable carbohydrate source for turbot juvenile growth.