In vitro induction of gonadal sex change in a protogynous fish, three-spotted wrasse (Halichoeres trimaculatus)

Recently, we succeeded in inducing in vitro spermatogenesis in a protogynous hermaphrodite fish, threespotted wrasse (Halichoeres trimaculatus), during organ culture of ovary with a serum-supplemented medium. In the pres- ent study, we further optimized and used this culture system to determine effective steroid doses to induce sex change, and to investigate the importance of apoptosis during sex change in vitro. The results show that the restructuring from ovary to testis in the wrasse could be induced in vitro with a serum-free medium. Gonadal sex change can be triggered during basic in vitro culture due to a lack of endogenous factors (especially, estrogens) for female sexuality, and can be accelerated by androgens. Furthermore, oocyte apoptosis may be an important mechanism effecting gonadal sex change.