Sex change in the protandrous black porgy, Acanthopagrus schlegeli: A review in gonadal development, estradiol, estrogen receptor, aromatase activityand gonadotropin

Black porgy, Acanthopagrus schlegeli Bleeker, a marine protandrous hermaphr odite, is functional male for the first two years of life but begins to sex ually change to female after the third year. Testicular tissue and ovarian tissue was separated by connective tissue in the bisexual gonad. This sex p attern provides a very good model to study the endocrine mechanism of sex c hange in fish. The annual profiles of plasma estradiol, vitellogenin and 11 -ketotestosterone concentrations in males were significantly different from those in the three-year-old females. Significantly high levels of plasma e stradiol 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 go nadal aromatase activity, plasma gonadotropin II levels and sex change in t he two-year-old fish. Exogenous estradiol administered for 5-6 months induc ed a reversible sex change in one- and two-year-old fish. The sensitive per iod for estradiol treatment of sex change is from early prespawning to spaw ning season. Implantation with testosterone for more than a year could not block the natural sex change in three-year-old fish. Exogenous aromatase in hibitors (1,4,6-androstatriene-3,17-dione or fadrozole) suppressed aromatas e activity in the brain. Oral administration with aromatase inhibitors for a year further inhibited the natural sex change in three-year-old black por gy and all fish became functional male with spermiation. Estrogen receptor a gene in the ovarian tissue of bisexual gonad is significantly less expres sed than that in the vitellogenic ovary of female on the basis of reverse-t ranscription polymerase-chain reaction. There was no difference in the annu al profiles of the plasma gonadotropin II levels in the males and natural i nversing females. Plasma gonadotropin II levels were significantly higher i n estradiol-treated group than those in the control. It is concluded that e stradiol, aromatase activity and estrogen receptor in the ovarian tissue pl ay an important role in the natural and controlled sex change in black porg y. The association of gonadotropin and sex change in black porgy is not cle ar. J. Exp. Zool. 290:715-726, 2001. (C) 2001 Wiley-Liss, Inc.