Influence of dietary zinc on growth, zinc bioaccumulation and expression of genes involved in antioxidant and innate immune in juvenile mud crabs (Scylla paramamosain)

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 center dot 5, 56 center dot 9, 68 center dot 5, 97 center dot 3, 155 center dot 6 or 254 center dot 7 mg/kg. Dietary Zn level significantly influenced percentage weight gain (PWG), with the highest observed in crabs fed the diet containing 97 center dot 3 mg/kg Zn. Tissue Zn concentrations significantly increased as dietary Zn levels increased from 44 center dot 5 to 254 center dot 7 mg/kg. Retention of Zn in hepatopancreas increased with dietary Zn levels up to 68 center dot 5 mg/kg and then significantly decreased. Moreover, inadequate dietary Zn (44 center dot 5 and 56 center dot 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 center dot 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 center dot 5 and 97 center dot 3 mg/kg Zn. The highest activities of phenoloxidase and alkaline phosphatase were recorded in crabs fed the diets containing 68 center dot 5 and 97 center dot 3 mg/kg Zn. Expression levels of prophenoloxidase and toll-like receptor 2 were higher in crabs fed the 97 center dot 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 center dot 9 mg/kg, with 68 center dot 5 to 97 center dot 3 mg/kg recommended for maintaining optimal Zn bioaccumulation, oxidation resistance and innate immune response of juvenile mud crabs.