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An 8-week feeding trial was conducted to evaluate the effects of dietary n-3 LC-PUFA levels on growth performance, tissue fatty acid profiles and relative expression of genes involved in the lipid metabolism of mud crab (Scylla paramamosain). Ten isonitrogenous diets were formulated to contain five n-3 LC-PUFA levels at 7 and 12 % dietary lipid levels. The highest weight gain and specific growth rate were observed in crabs fed the diets with 19·8 and 13·2 mg/g n-3 LC-PUFA at 7 and 12 % lipid, respectively. Moisture and lipid contents in hepatopancreas and muscle were significantly influenced by dietary n-3 LC-PUFA at the two lipid levels. The DHA, EPA, n-3 LC-PUFA contents and n-3:n-6 PUFA ratio in hepatopancreas and muscle significantly increased as dietary n-3 LC-PUFA levels increased at both lipid levels. The expression levels of -6 fatty acyl desaturase and acyl-CoA oxidase in hepatopancreas increased significantly, and expression levels of fatty acid synthase, carnitine palmitoyltransferase I and hormone-sensitive TAG lipase were down-regulated, with increased dietary n-3 LC-PUFA regardless of lipid level. Based on weight gain, n-3 LC-PUFA requirements of S. paramamosain were estimated to be 20·1 and 12·7 mg/g of diet at 7 and 12 % dietary lipid, respectively. Overall, dietary lipid level influenced lipid metabolism, and purified, high-lipid diets rich in palmitic acid reduced the n-3 LC-PUFA requirement of juvenile mud crab.
The aim of the present study was to investigate the effects of dietary Zn level on growth performance, Zn bioaccumulation, antioxidant capacity and innate immunity in juvenile mud crabs (Scylla paramamosain). Six semi-purified diets were formulated to contain dietary Zn levels of 44·5, 56·9, 68·5, 97·3, 155·6 or 254·7 mg/kg. Dietary Zn level significantly influenced percentage weight gain (PWG), with the highest observed in crabs fed the diet containing 97·3 mg/kg Zn. Tissue Zn concentrations significantly increased as dietary Zn levels increased from 44·5 to 254·7 mg/kg. Retention of Zn in hepatopancreas increased with dietary Zn levels up to 68·5 mg/kg and then significantly decreased. Moreover, inadequate dietary Zn (44·5 and 56·9 mg/kg) reduced antioxidation markers including total superoxide dismutase (SOD) and Cu/Zn SOD activities and total antioxidant level. Crabs fed the diet with 44·5 mg/kg Zn also showed significantly lower expression of genes involved in antioxidant status, such as Cu/Zn SOD, glutathione peroxidase, catalase and thioredoxin than those fed diets containing 68·5 and 97·3 mg/kg Zn. The highest activities of phenoloxidase and alkaline phosphatase were recorded in crabs fed the diets containing 68·5 and 97·3 mg/kg Zn. Expression levels of prophenoloxidase and toll-like receptor 2 were higher in crabs fed the 97·3 mg/kg Zn diet compared with crabs fed the other diets. Based on PWG alone, the optimal dietary Zn level was estimated to be 82·9 mg/kg, with 68·5 to 97·3 mg/kg recommended for maintaining optimal Zn bioaccumulation, oxidation resistance and innate immune response of juvenile mud crabs.
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