Effect of temperature on the efficiency of feminization of medaka (Oryzias latipes) by hormonal (estradiol) manipulation

During the critical time of sex determination, fish gonads are liable to chemicals and environmental factors that can disrupt the normal course of sex differentiation. This study was conducted to examine the possibility of a combined effect of water temperature and an exogenous steroid hormone (estradiol-17β, E₂) on the process of sex differentiation of Japanese medaka (Oryzias latipes) of the d-rR strain. Sex reversal experiments conducted at different temperatures (14, 18, 22, 26, 30, and 34 °C) and E₂ concentrations (0, 1 and 10 ppb) showed that the percentage of feminization of genotypic males into phenotypic females decreased with increasing temperature for both E₂ concentrations, suggesting a marked synergism between the two factors.