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.

No abstract

Two year old black porgy (Acanthopagrus schlegeli) fed a diet containing 4.0 mg kg(-1) of estradiol-17β (E2) for 5 months had significantly lower GSI than the control group during the spawning season. E2 suppressed testicular development, spermiation and plasma testosterone (T) and 11-ketotestosterone (11-KT) and stimulated ovarian development, vitellogenesis and sex reversal. Spermiation in the control group occurred in January and February with the concentrations of 1.08-1.36 × 10(10) sperm ml(-1) of milt. Higher plasma T and 11-KT, but lower E2 levels were detected in the spermiating fish (control group). Higher plasma E2 levels were detected in the sex reversing black porgy during the pre-spawning season. A sharp rise in plasma 11-KT and a drop in T levels were detected in spermiating fish (control group) from January to February. Plasma 11-KT levels correlated with the testicular development and spermiation. The data suggest that E2 plays an important role in controlling the sex reversal of black porgy.

The objective was to investigate the effects of estradiol-17β (E 2 ) on gonadal development, spermiation, gonadal aromatase activity, and the concentrations of plasma sex steroids and vitellogenin in 2-year-old protandrous black porgy, Acanthopagrus schlegeli. Black porgy were divided into two groups, one fed a control diet and the other a diet mixed with E 2 (4.0 mg/kg feed) for 4½ months. Significantly lower GSI was observed in the E 2 group. Fish treated with E 2 showed completely suppressed spermiation, and 38% had developing vitellogenic oocytes in the gonad (an evidence of sex reversal in 2-year-old fish). Higher gonadal aromatase activity and plasma E 2 concentrations and lower concentrations of plasma 11-ketotestosterone (11-KT) were observed in the E 2 group. After finishing 4½ months of E 2 treatment in the early spawning season, the gonadosomatic index increased and spermiation resumed in the E 2 group (which was fed a control diet) during the mid-or late-spawning season. Steadily increasing levels of plasma T and 11-KT and decreasing gonadal aromatase activity and plasma vitellogenin concentrations were observed in the E 2 group. The present data show that E 2 induced a temporary and reversible sex change (only a small proportion of the fish). Elevated aromatase activity in gonads, elevated E 2 levels in plasma, and diminished levels of plasma 11-KT are associated with the occurrence of sex reversal in protandrous black porgy. J. Exp. Zool. 280:165173, 1998 Black porgy, Acanthopagrus schlegeli Bleeker, a widely distributed marine protandrous hermaphrodite, is of particular interest for commercial aquaculture in parts of Asia (Chang and Yueh, '90a). The fish are functional males for the first 2 years of life but begin to change sex during the third year. Only about 40% of cultured black porgy change to females, whereas the rest remain in the male phase during the spawning season in the 3-or 4-year-old fish (Chang et al., '94). Black porgy in Taiwan have an annual reproductive cycle with a pattern of multiple spawning occurring in later winter and early spring.High levels of plasma estradiol-17β (E 2 ) during the prespawning and spawning season are likely correlated with the natural sex reversal of 3-year-old black porgy (Chang et al., '94). Oral administration of E 2 (4 mg per kg of feed) for at least 5 months induced sex reversal in 2-year-old black porgy with vitellogenic oocytes in the gonads (Chang et al., '95a). E 2 also induced sex reversal in 1-year-old black porgy; however, the ovary remained at the stage of primary oocytes (Chang et al., '94, '95a, b). We conclude that E 2 likely plays an important role in the natural and control sex reversal in protandrous black porgy.Our previous data still could not answer the question of whether the reversed fish will undergo full ovarian development or reverse to males in the absence of any further treatment. Further experimentation still needs to be studied in order to understand better the mechanism and control of sex reversal in black porgy.And...

No abstract