Environmentally relevant exposure of 17α-ethinylestradiol impairs spawning and reproductive behavior in the brackish medaka Oryzias melastigma

•Reproductive and behavioral effects of EE2 was tested in Oryzias melastigma.•Inhibited spawning and reproductive behavior were observed at 50 and 100ng/L EE2.•Spermatogenesis was normal in the male fish with suppressed reproductive behavior.•Reproductive behavior of O. melastigma can be used as an ecotoxicological endpoint. We assessed the effects of 17α-ethinylestradiol (EE2) on spawning and reproductive behavior of the brackish medaka Oryzias melastigma at environmental concentrations. Breeding pairs were exposed to EE2 at either lower concentrations (0, 1, and 10ng/L) or higher concentrations (0, 50, and 100ng/L) for 14days. Swimming performance and reproductive behavior (following, dancing, and copulation) of the males were analyzed at the end of exposure. Additionally, gonad histology was conducted in the males in the higher EE2 experiment. We found that spawning was significantly inhibited in the 50–100ng/L EE2 groups. Swimming performance was not affected in all groups. Dancing and copulation were significantly suppressed in the 50–100ng/L groups. No effect was observed in testis histology in the 50–100ng/L groups. Our data suggests that reproductive behavior of O. melastigma can be utilized as a behavioral endpoint for ecotoxicology studies of endocrine disruptors in estuarine/marine environments.