Long-term exposure of the binary mixture of cadmium and mercury damages the developed ovary of adult zebrafish

The toxicity of the binary mixture of cadmium (Cd) and mercury (Hg) on the ovary of adult zebrafish was evaluated in the present study. Adult female zebrafish were exposed to cadmium chloride (1 mg/L), mercury chloride (30 mu g/L), and a binary mixture of both metals for 21 days. The toxic effects of both metals on the ovary were investigated by evaluating the oxidative stress markers and related gene expression in ovarian tissue along with the histopathological examination. The significantly decreased level of GSH and increased level of MDA in ovarian tissue of adult female zebrafish exposed to Cd + Hg indicated that the exposure of binary mixture of Cd and Hg caused more lipid peroxidation in the ovary. The significant changes in expression of mRNA of catalase (CAT) and nuclear factor erythroid 2 (NF-E2)-related factor 2 (Nrf2) were not observed in the ovary of zebrafish exposed to the binary mixture. Upon histological evaluation, a decreased number of full-growth (mature) oocytes along with degenerative changes due to Cd exposure were noticed, while ovary of zebrafish of the Hg-exposed group had shown a decreased number of pre-and early vitellogenic oocytes along with atretic previtellogenic oocytes compared to the control group. The ovary of zebrafish of the Cd +Hg-exposed group had shown a decreased number of previtellogenic oocytes with marked pathological changes in mature oocytes. Present findings elucidate that simultaneous long-term exposure of Cd and Hg compared to individual exposure significantly damaged the various stages of oocytes of an ovary of adult zebrafish.