SEASONAL-CHANGES IN SERUM STEROID-HORMONES IN A PROTANDROUS TELEOST, THE SOBAITY (SPARIDENTEX-HASTA VALENCIENNES)

Serum concentrations of 11‐ketotestosterone, 11β‐hydroxytestosterone, testosterone, testoster‐one glucuronide, oestradiol and 17,20β ‐dihydroxy‐4‐pregnen‐3‐one (17,20β ‐P) were measured in the sobaity at monthly intervals through their second breeding season. Concentrations of the 11‐oxygenated androgens in the males and of oestradiol in the females peaked during the spawning season in January‐February, while maximum levels of testosterone were found in the summer when these steroids were low. Testosterone glucuronide showed two peaks, one in the post‐spawning period as oestradiol and the 11‐oxygenated androgens were falling and the other coincident with the summer peak of testosterone. 17,20β ‐P was detectable in only one male and one female fish in February. Serum concentrations of 11‐oxygenated androgens are more reliable than those of oestradiol for determining the sex of sobaity, and may also be used as indicators of the occurrence of sex reversal. The seasonal pattern of serum steroids correlated well with the changes of sexual status of the gonads during regression and recrudescence observed histologically and suggests that oestradiol may be involved in the sex inversion of this species. Copyright © 1991, Wiley Blackwell. All rights reserved