In vertebrates, gonadal steroids play a fundamental role in sex differentiation, sexual maturation and reproductive behaviour. In teleost females, sex steroids are involved in the regulation of vitellogenesis and oocyte final maturation with increasing plasma levels through the reproductive cycle. In gonochoric species a possible role of 11ß-hydroxylation on male sexual determination has been suggested. In hermaphrodite protogynous fish, the intersexual stage appears to be characterised by a 11ketotestosterone decrease and a 11ß hydroxyandrostenedione increase. Till now, few endocrinological studies on sexual steroids in ambisexual fish are available and none on the protogynous hermaphrodite Epinephelus marginatus. This study reports on plasma levels of sex steroids during the spawning period in relation to sex and maturity stages in a wild population of E. marginatus. Gonad specimens (n=91), Bouin’s fixed, and related plasma samples, were submitted to histological studies and to RIAs for sex steroids. 17ß-estradiol (17ß-E), testosterone (T), 11-ketotestosterone (11-KT) and 11ß-hydroxyandrostenedione (11ß-OHA) were assayed. Oocytes at different stages of development in mature females during the reproductive period were observed together with the presence of high 17ß-E and T plasma levels. Plasma levels of 17ß-E in males remained low through the reproductive period. In transitional, 17ß-estradiol levels were lower than in females but higher than in males. Increasing values of 11ß-OHA were observed in transitionals at the beginning of sex inversion with gonads characterised by previtellogenic oocytes and extensive proliferation of interstitial tissue. Plasma levels of 11-KT were higher in males than in transitionals and in vitellogenic females. In conclusion, 17ß-E and T, taken together, could be considered as good indicators of functional gonad state in E. marginatus. 11ß-hydroxyandrostenedione appeared to be the most reliable marker of sex inversion.
Plasma sex steroid levels and maturity stages in wild Epinephelus marginatus
MANDICH, ALBERTA;MASSARI, ALESSANDRA;
1998-01-01
Abstract
In vertebrates, gonadal steroids play a fundamental role in sex differentiation, sexual maturation and reproductive behaviour. In teleost females, sex steroids are involved in the regulation of vitellogenesis and oocyte final maturation with increasing plasma levels through the reproductive cycle. In gonochoric species a possible role of 11ß-hydroxylation on male sexual determination has been suggested. In hermaphrodite protogynous fish, the intersexual stage appears to be characterised by a 11ketotestosterone decrease and a 11ß hydroxyandrostenedione increase. Till now, few endocrinological studies on sexual steroids in ambisexual fish are available and none on the protogynous hermaphrodite Epinephelus marginatus. This study reports on plasma levels of sex steroids during the spawning period in relation to sex and maturity stages in a wild population of E. marginatus. Gonad specimens (n=91), Bouin’s fixed, and related plasma samples, were submitted to histological studies and to RIAs for sex steroids. 17ß-estradiol (17ß-E), testosterone (T), 11-ketotestosterone (11-KT) and 11ß-hydroxyandrostenedione (11ß-OHA) were assayed. Oocytes at different stages of development in mature females during the reproductive period were observed together with the presence of high 17ß-E and T plasma levels. Plasma levels of 17ß-E in males remained low through the reproductive period. In transitional, 17ß-estradiol levels were lower than in females but higher than in males. Increasing values of 11ß-OHA were observed in transitionals at the beginning of sex inversion with gonads characterised by previtellogenic oocytes and extensive proliferation of interstitial tissue. Plasma levels of 11-KT were higher in males than in transitionals and in vitellogenic females. In conclusion, 17ß-E and T, taken together, could be considered as good indicators of functional gonad state in E. marginatus. 11ß-hydroxyandrostenedione appeared to be the most reliable marker of sex inversion.
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