Parental cadmium exposure during the spawning period reduces cadmium sensitivity through the antioxidant system in rare minnow (Gobiocypris rarus) larvae.

Cadmium (Cd) is a noxious heavy metal widely dispersed in aquatic systems. Parental Cd exposure of fish species at environmental concentrations has been shown to cause deformities and stunted growth in their offspring. However, the long-term effects and the mechanisms underlying parental Cd exposure in fish species on Cd sensitivity in their offspring remain unclear. To explore the impacts of parental Cd exposures on Cd sensitivity, rare minnow (Gobiocypris rarus) larvae whose parents were exposed to Cd at 0, 5 or 10 μg/L for 28 days were established. Results showed that parental Cd exposure in rare minnow increased the Cd content of its larvae. In terms of malformation rate, mortality rate and total length at 7 days of rare minnow larvae, parental Cd exposure at 5 or 10 μg/L reduced Cd sensitivity. Further mechanistic investigation demonstrated that parental Cd exposure significantly upregulated the expression of antioxidant gene regulated by nuclear factor erythroid 2-related factor 2 (Nrf2) and nuclear factor-kappa B (NF-кB) in rare minnow larvae. In addition, parental Cd exposure significantly elevated the level of reactive oxygen species (ROS) and malondialdehyde (MDA), but markedly decreased catalase (CAT), superoxide dismutase (SOD) and oxidized glutathione (GST) activity. The impact of parental Cd exposure to metallothionein (MT) content and the expression of MT mRNA, a detoxifying metallothionein, showed that parental Cd exposure of rare minnow induced oxidative stress in the larvae. Meanwhile, these results indicated that parental Cd exposure in rare minnow reduced the Cd sensitivity of the larvae via activating the Nrf2-mediated antioxidant system. This project helps us to further understand the toxicological mechanism of Cd in fish species and properly assess its potential ecological risk.