ESTRADIOL-17-BETA SUPPRESSES TESTICULAR DEVELOPMENT AND STIMULATES SEX REVERSAL IN PROTANDROUS BLACK PORGY, ACANTHOPAGRUS-SCHLEGELI

Two year old black porgy (Acanthopagrus schlegeli) fed a diet containi ng 4.0 mg kg(-1) of estradiol-17 beta (E(2)) for 5 months had signific antly lower GSI than the control group during the spawning season. E(2 ) suppressed testicular development, spermiation and plasma testostero ne (T) and 11-ketotestosterone (11-KT) and stimulated ovarian developm ent, vitellogenesis and sex reversal. Spermiation in the control group occurred in January and February with the concentrations of 1.08-1.36 x 10(10) sperm ml(-1) of milt. Higher plasma T and 11-KT, but lower E (2) levels were detected in the spermiating fish (control group). High er plasma E(2) levels were detected in the sex reversing black porgy d uring 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 Ja nuary to February. Plasma 11-KT levels correlated with the testicular development and spermiation. The data suggest that E(2) plays an impor tant role in controlling the sex reversal of black porgy.