Ovotestis in a Japanese Medaka

Abstract We observed ovotestis in Japanese medaka Oryzias latipes used to study the effects of bromodichloromethane (BDCM) on gonadal differentiation. Bromodichloromethane, a trihalomethane, is a drinking water disinfection byproduct. Seven-day-old Japanese medaka (n = 30 fish per treatment) were exposed for 10 d to nominal concentrations of BDCM (10 or 25 mg/L) in dimethyl sulfoxide, a carrier solvent control, or a springwater control, then transferred to springwater and reared for 6 months. Ovotestis was present in one female of the 13 Japanese medaka that survived for 6 months after exposure to 10 mg/L BDCM. This is the first report of an intersex condition in a BDCM exposure study. There are no known reports of spontaneous occurrences of ovotestis in Japanese medaka; however, we cannot eliminate the possibility that this single case was spontaneous rather than induced by BDCM. Therefore, further studies with a wide range of concentrations of BDCM are needed to confirm the ovotestis induction potential...