Environmentally relevant concentrations of mercury inhibit the growth of juvenile silver carp (Hypophthalmichthys molitrix): Oxidative stress and GH/IGF axis.

Mercury (Hg) is a global environmental contaminant, and excessive mercury levels in water can adversely affect the growth of fish. Silver carp (Hypophthalmichthys molitrix) is one of the important freshwater aquaculture fish in China, and its natural resources have been critically declining. However, the effects of Hg exposure on the growth hormone/insulin-like growth factor (GH/IGF) axis and its toxic mechanism are still unclear. In this study, we systematically evaluated the bioaccumulation, histomorphology, antioxidant status, hormone levels, and GH/IGF axis toxicity of juvenile silver carp after exposure to environmental-related concentrations of Hg (0, 0.05, 0.5, 5, and 50 µg/L) for 28 days. Results showed that the Hg bioaccumulation in the liver increased with a rise in Hg concentration and time of exposure. The body length (BL), body weight (BW), weight growth rate (WGR) and specific growth rate (SGR) all decreased after Hg exposure. The serum levels of growth hormones (GH and IGF) and thyroid hormones (T3 and T4) were significantly decreased, and the expressions of GH/IGF axis-related genes were significantly downregulated after 7, 14, and 28 days of Hg exposure. Correlations between the growth parameters and growth hormones or expression of genes in GH/IGF axis further suggested that environmentally relevant concentrations of Hg could have adverse effects on growth. In addition, with increasing Hg exposure, superoxide activities of dismutase (SOD), catalase (CAT), and glutathione S-transferase (GST)and levels of reduced glutathione (GSH) and malondialdehyde (MDA) were significantly increased, whereas the activity of glutathione peroxidase (GPx) significantly decreased and oxidative stress-related gene significantly changed. Liver lesions were mainly characterized by inflammatory cell infiltration, hepatocyte necrosis and fat vacuolation after exposure to Hg. Taken together, the results indicate that Hg exposure leads to growth inhibition and oxidative stress in juvenile silver.