In this study, we investigated the effects of different carbohydrate-to-lipid ratios in the dietary on the growth, glucose metabolism and lipid metabolism of juvenile turbot (Scophthalmus maximus L.), aiming to identify the optimal carbohydrate-lipid ratio in feed for turbot and to determine the relative utilization efficiency of carbohydrates and lipids. Five experimental diets with different carbohydrate-to-lipid ratios (2.01, 1.53, 1.25, 0.96, and 0.71) were used, and these diets were fed to five groups of juvenile turbot (D1, D2, D3, D4, D5). Turbots with an initial weight of (7.00±0.35) g were randomly allocated to 15 tanks, 40 individuals each. Feeding was conducted twice daily using satiation feeding strategy in a culture period of 56 days. The results showed that the weight gain rate, specific growth rate, protein efficiency ratio, and feed efficiency ratio of turbot in D4 group were significantly higher than those in other groups (P < 0.05). The activities of trypsin and lipase in the intestines were significantly higher in D4 group than in others while the amylase activity was significantly higher in D3 group than in others (P < 0.05). The content of plasma triglycerides in D3 and D4 groups was significantly higher than that in other groups (P < 0.05). In contrast, the levels of total cholesterol, HDL-C, and LDL-C in D4 group were significantly higher than those in other groups (P < 0.05). The expression of glucose kinase gene in liver was significantly higher in D3 group than in D1 group. The the expression of pyruvate kinase gene was significantly higher in D3 and D4 groups than in other groups. The expression of phosphofructokinase 1 gene was significantly higher in D4 group than in other groups. The expression levels of phosphoenolpyruvate carboxykinase, fructose-1, 6-bisphosphatase and glucose-6-phosphatase genes in liver were significantly higher in D5 group than in other groups (P < 0.05). The D4 group exhibited significantly higher expression of peroxisome proliferator-activated receptor-γ coactivator-1α and lipin1 genes in liver compared to other groups. The expression of peroxisome proliferator-activated receptor α was significantly higher in D5 group than in other groups. The expression of lipoprotein lipase gene was significantly higher in D4 and D5 groups than in other groups. The expression of liver X receptor was significantly higher in D3, D4 and D5 groups than in D1 and D2 groups (P < 0.05). In summary, the optimal physiological and growth performance of turbot was observed when the carbohydrate-to-lipid ratio in the diet varied between 0.96 and 1.25.

To investigate the effects of mTOR signaling pathway on the growth, antioxidant and non-specific immunity of Litopenaeus vannamei, three isonitrogen and isoenergy compound diets were designed, which were named control (Con), leucine (Leu) and rapamycin (Rap) groups, respectively. One percent of alanine (Ala) was added to the Con group, 1% of leucine to Leu group, and 0.003% of rapamycin to Rap group. Litopenaeus vannamei with initial body weight of (0.70±0.01) g was selected for culture experiment in an indoor circulating water system, 3 replicates each group, 60 shrimp each replicate. The culture cycle was 56 days. At the end of culture, the growth, antioxidant and non-specific immunity related indexes were analyzed. The results showed that the specific growth rate of Leu group was significantly higher than that of Con group, and the specific growth rate of Rap group was significantly lower than that of Con group (P < 0.01). The phosphorylation level of muscle S6 protein in prawn was the strongest at 1h after feeding, and then gradually decreased. Compared with Con group, the 1h muscle S6 protein phosphorylation level in Leu group was significantly increased, and the 1 h muscle S6 protein phosphorylation level in Rap group was significantly decreased (P < 0.05). In the serum of shrimp, the activities of alkaline phosphatase and phenoloxidase in Leu group were significantly higher than those in control group (P < 0.05), and the activities of acid phosphatase in Rap group were significantly lower than those in Con group (P < 0.05). In the hepatopancreas of shrimp, the activities of catalase, total antioxidant enzymes and phenoloxidase in Leu group were significantly higher than those in Con group (P < 0.05), and the malondialdehyde content in Leu group was significantly lower than that in Rap group (P < 0.05). The relative expression levels of Lysozyme, C-MnSOD and Lectin in Leu group were significantly higher than those in Con group (P < 0.05), and the relative expression levels of Relish and Hsp70 in Rap group were significantly lower than those in Con group (P < 0.05). The results showed that dietary leucine can effectively activate the mTOR signaling pathway, thereby improving the growth performance, antioxidant and non-specific immunity of Litopenaeus vannamei. The addition of rapamycin can effectively inhibit the mTOR signaling pathway, and inhibit the growth performance, antioxidant and immune function of Litopenaeus vannamei.

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.