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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 µg/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 decreased expression of mRNA of catalase (CAT) and Nuclear factor erythroid 2 (NF-E2)-related factor 2 (Nrf2) were observed in the ovary of zebrafish exposed to binary mixture. The down regulation of Nrf2 might be responsible for suppression of the antioxidant system which resulted in cellular alterations in the ovary. 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 Hg-exposed group had shown decreased number of pre- and early-vitellogenic oocytes along with atretic pre-vitellogenic oocytes compared to the control group. The ovary of zebrafish of Cd + Hg-exposed group had shown decreased number of pre-vitellogenic oocytes with marked pathological changes in mature oocytes. Present findings elucidate that simultaneous long-term exposure of Cd and Hg may significantly affect the ovary through alteration of Nrf2 mediated cascade in adult zebrafish.

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