Estradiol, aromatase and steroid receptors involved in the sex change of protandrous black porgy, Acanthopagrus schlegeli

Abstract

Black porgy, Acanthopagrus schlegeli, a marine protandrous hermaphrodite, is functionally male for the first 2 years of its life, but begins to sexually change to female after the third year. Testicular tissue and ovarian tissue are separated by connective tissue in the bisexual gonad. This sex pattern provides a unique model for studying the mechanism of sex change in fish. Significantly high levels of plasma estradiol during the prespawning/spawning season, and low levels of plasma 11-ketotestosterone during the spawning season were observed in the inversing females. No difference of plasma testosterone levels was observed in males and females. Oral administration of estradiol stimulated high levels of gonadal aromatase activity, plasma luteinizing hormone levels and sex change in the 2-year-old fish. Oral administration with aromatase inhibitors for a year further blocked the natural sex change in 3-year-old black porgy and all fish became functional males. Transcripts of estrogen receptor and androgen receptor in the ovarian tissue of the bisexual gonad were significantly less expressed than those in the bisexual ovarian tissue. The estrogen receptor transcripts were much higher in the vitellogenic ovary than those in the bisexual ovarian tissue. It was concluded that estradiol, aromatase and steroid receptors in the gonadal tissue play an important role in the natural and controlled sex change in black porgy.