The objectives of this study were to investigate the seasonal changes of steroid profiles, estradiol-17 beta (E2), testosterone (T), and 17 alpha-hydroxyprogesterone (17 alpha-OH P), among female, male, and reversing female black porgy, Acanthopagrus schlegeli. The experimental induction of sex reversal in juvenile black porgy by exogenous E2 was also studied. Three-year-old male (n=8) and four-year-old female (n=7) black porgy were selected for the experiment of seasonal changes of steroid profiles. Blood samples were collected from each fish at 2 week intervals for 8 months. Plasma samples in three-year-old males were further classified to those of males (n=4) and reversing females (n=4) based on the sexual stage of the gonad at the end of the experiment. Plasma E2 profiles in males were significantly different from those in the reversing females. Peak levels of plasma E2 in the females and reversing females occurring during the early prespawning season were similar. Lower levels of plasma E2 were, however, observed in the males. Plasma T did not differ significantly in females, males or reversing females. Low and constant levels of plasma 17 alpha-OH P were observed in each group of fish. In the experimental induction of sex reversal, oral administration of E2 (4 mg per kg of feed) for 5 months suppressed the spermiation and inhibited gonadal growth but successfully induced the precocious sex change at the prespawning stage in one-year-old black porgy. Ovarian tissue with primary oocytes was predominant in the gonads of E2-fed fishes. Our data suggest that high levels of plasma E2 in the prespawning and spawning season are likely correlated with the natural sex reversal of black porgy. E2 likely plays an important role in sex reversal of protandrous black porgy. (C) 1994 WiIey-Liss, Inc.
