Black porgy, Acanthopagrus schlegeli Bleeker, a marine protandrous hermaphrodite, is functional male for the first two years of life but begins to sexually change to female after the third year. Testicular tissue and ovarian tissue was separated by connective tissue in the bisexual gonad. This sex pattern provides a very good model to study the endocrine mechanism of sex change 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 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 gonadotropin II levels and sex change in the two-year-old fish. Exogenous estradiol administered for 5-6 months induced a reversible sex change in one- and two-year-old fish. The sensitive period for estradiol treatment of sex change is from early prespawning to spawning season. Implantation with testosterone for more than a year could not block the natural sex change in three-year-old fish. Exogenous aromatase inhibitors (1,4,6-androstatriene-3,17-dione or fadrozole) suppressed aromatase activity in the brain. Oral administration with aromatase inhibitors for a year further inhibited the natural sex change in three-year-old black porgy and all fish became functional male with spermiation. Estrogen receptor alpha gene in the ovarian tissue of bisexual gonad is significantly less expressed than that in the vitellogenic ovary of female on the basis of reverse-transcription polymerase-chain reaction. There was no difference in the annual profiles of the plasma gonadotropin II levels in the males and natural inversing females. Plasma gonadotropin II levels were significantly higher in estradiol-treated group than those in the control. It is concluded that estradiol, aromatase activity and estrogen receptor in the ovarian tissue play an important role in the natural and controlled sex change in black porgy. The association of gonadotropin and sex change in black porgy is not clear.

The objectives of the present study were to investigate the effects of oral administration of aromatase inhibitors on sex change, milt volume, 11-ketotestosterone (11-KT), and LH in plasma; aromatase activity in gonad, pituitary, and brain in the protandrous fish, black porgy (Acanthopagus schlegeli Bleeker). Two-year-old functional male black porgy were divided into two groups; one was fed a control diet and the other was fed a diet mixed with aromatase inhibitors (AIs; fadrozole and 1,4,6-androstatriene-3,17-dione, each 10 mg/kg feed) for 8.5 mo. A significantly higher gonadosomatic index was observed in the AI group. Fish treated with AIs showed complete suppression of natural sex change. Significantly higher levels of plasma 11-KT, LH, and milt volume were shown in the AI group than the controls. Lower aromatase activity in the gonad, pituitary, forebrain, midbrain, and hindbrain in concordance with the suppression of sex change was observed in the AI group. The data show that aromatase is directly involved in the mechanism of natural sex change of protandrous black porgy. AIs also enhanced male function in concordance with the elevated plasma levels of 11-KT and spermiation in milt volume.

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