Role of estrogen in spermatogenesis in initial phase males of the three-spot wrasse (Halichoeres trimaculatus): Effect of aromatase inhibitor on the testis

The three-spot wrasse, Halichoeres trimaculatus, is a protogynous hermaphrodite. Under appropriate social conditions, female fish can become male. Previous studies indicated that estrogens are important regulators of sex change in this fish. However, the role of estrogen in the male is not known. To clarify the involvement of estrogen in spermatogenesis in hermaphrodite fish, we treated initial phase (IP) males for 10 weeks with exemestane, an aromatase inhibitor (AI), to block estrogen synthesis. Fish treated with AI exhibited decreases in gonadal weight, plasma estrogen levels, and spermatogonial proliferation in the testis, together with increases in androgen levels. Additionally, we confirmed that exogenous estrogen treatments stimulated the renewal and proliferation of spermatogonia in the testis of IP males. These results indicate that estrogens play an important role in regulating spermatogenesis in this fish.