Transgenerational hormesis of environmentally relevant concentrations of cadmium and zinc in marine medaka Oryzias melastigma subjected to different salinity conditions.

The effects of zinc (Zn) and cadmium (Cd) on aquatic species throughout generations at varying salinities are mostly unknown. In this study, marine medaka Oryzias melastigma F1 larvae were exposed to 500 μg/L Zn or 2.5 μg/L Cd at 5 ‰ and 25 ‰ salinities for 25 days, and then recovered for 65 days, allowing them to produce F2 larvae. Growth was stimulated by Cd in F1 larvae at 5 ‰ salinity. Cd and Zn inhibited oxidative stress in F2 larvae at both salinities. Cortisol levels of the F2 larvae were elevated at 5 ‰ salinity and declined at 25 ‰ salinity after F1 larval were exposed to Zn. However, cortisol levels in both F1 exposed to Cd and their offspring F2 increased at 5 ‰ salinity. The observed physiological alterations may be largely attributed to the genes involved in regulating the hypothalamus-pituitary-interrenal (HPI) axis, the growth hormone/insulin-like growth factor-I (GH/IGF) axis, the NF-E2-related factor 2 (Nrf2) signaling pathway. In summary, the current work is the first to show that ecologically relevant Cd and Zn have transgenerational effects in a salinity-dependent manner in fish. It is crucial to account for transgenerational hormesis in the ecological risk assessment of chemicals.