Diet supplementation of organic zinc positively affects growth, antioxidant capacity, immune response and lipid metabolism in juvenile largemouth bass, Micropterus salmoides .

Zinc is an important trace element involved in various biochemical processes in aquatic species. An 8-week rearing trial was thus conducted to investigate the effects of zinc on juvenile largemouth bass ( Micropterus salmoides ) by feeding seven diets respectively supplemented with no zinc (Con), 60 and 120 mg kg -1 inorganic zinc (Sul60, Sul120), 30, 60, 90 and 120 mg kg -1 organic zinc (Bio30, Bio60, Bio90, Bio120). Sul120 and Bio120 groups showed significantly higher weight gain and specific growth rate than Con group, with Bio60 group obtaining the lowest viscerosomatic index and hepatosomatic index. 60 or 90 mg kg -1 organic zinc significantly facilitated whole body zinc retention. Up-regulation of hepatic superoxide dismutase, glutathione peroxidase and catalase activities and decline of MDA contents indicated augmented antioxidant capacities by organic zinc. Zinc treatment also lowered plasma aminotransferase levels while promoting acid phosphatase activity and hepatic transcription levels of alp1 , acp1 and lyz-c than deprivation of zinc. The alterations in whole body and liver crude lipid and plasma triglyceride contents illustrated the regulatory effect of zinc on lipid metabolism, which could be possibly attributed to the changes in hepatic expressions of acc1 , pparγ , atgl and cpt1 . These findings demonstrated the capabilities of zinc in potentiating growth and morphological performance, antioxidant capacity, immunity as well as regulating lipid metabolism in M. salmoides . Organic zinc could perform comparable effects at same or lower supplementation levels than inorganic zinc, suggesting its higher efficiency. 60 mg kg -1 supplementation of organic zinc could effectively cover the requirements of M. salmoides .