Effects of cadmium exposure on tissue structure, antioxidant enzyme activity, serum biochemical indices and gene expression in the liver of juvenile largemouth bass (Micropterus salmoides)

This study aimed to understand the effect of various levels of waterborne cadmium exposure and associated integrated response in largemouth bass (Micropterus salmoides). The experimental fish were randomly divided into 4 groups: Group H (high concentration group): 0.25 mg/L of water (100% of the LC50); Group M (medium concentration group): 0.01 mg/L of water (50% of the LC50); group L (low concentration group): 0.05 mg/L of water (12.5% of the LC50) and group C (control). Experimental fish in group C (control group) were cultured in cadmium (Cd)-free tap water. After 28 days of Cd exposure, the gill and liver tissues were collected for histological analysis and antioxidant enzyme activities assay. Serum biochemical indices and the expression levels of HSP70, HSP90, Cyp1a, and MT in the liver were assayed. Results indicated Cd exposure in group H could significantly damage the gill and liver. The SOD activity of gill and liver exhibited an increasing trend with Cd concentrations increasing, and SOD activities increased significantly in group M compared to that of group C. Still, SOD activity significantly decreased in group H. MDA content increased significantly in both the gill and liver, while T-AOC activities were not significantly different in both the gill and liver. By comparison with group C, the activities of ALT and AST in serum were significantly increased in group M and group H; the contents of ALB and TP significantly decreased in group M and group H except for the content slightly increased in the group L; the contents of GLU, TG, and TC did not show significant changes in the group L and the group M, but increased significantly in the group H. The expression levels of HSP70 and HSP90 in the liver exhibited the highest level in group M, whereas the expression levels of MT and Cyp1a were highest in groups H and L, respectively. Our results are intended to provide a reference basis for the safety risk evaluation of Cd and healthy fish farming.