Cortisol Administration Induces Sex Change from Ovary to Testis in the Protogynous Wrasse, <b><i>Halichoeres trimaculatus</i></b>

Steroid hormones have been shown to play important roles in triggering sex change. However, the upstream mechanism that regulates the secretion of sex steroid hormones controlling sex change is not yet known. Cortisol, the primary glucocorticoid in teleost fish, is known to exhibit anti-stress action and is involved in many physiological functions, including regulation of steroidogenesis. Therefore, cortisol could be one of the candidate factors involved in the onset of sex change. In this study, we investigated the role of cortisol in sex change in the three-spot wrasse, Halichoeres trimaculatus, by prolonged administration of cortisol. Our results showed that gonads of all individuals treated with cortisol (1,000 µg/g diet) for 6 weeks contained spermatogenic germ cells. One of them exhibited matured testes with an ovarian cavity, indicating sex change. Additionally, the plasma estradiol-17β level in the cortisol treatment group was significantly lower than in the control group suggesting that cortisol plays a direct and/or indirect role in the regulation of estrogen production. These data imply that cortisol might be involved in the regulation of steroidogenesis by causing a decrease in the estrogen level, leading to the onset of sex change.