Abstract
The objective was to investigate the effects of various doses of estradiol-17β (E2) on a gonadal development, gametogenesis, and plasma levels of sex steroids in 1-year-old protandrous male black porgy, Acanthopagrus schlegeli . Juvenile black porgy were divided into four groups, fed with control diet or diet mixed with E2 (0.25, 1.0, or 4.0 mg/kg feed) for 7 months, respectively. Significantly higher gonadosomatic index was observed in the 0.25- and 1.0-mg E2 groups compared to that in the control and 4.0-mg E2 groups during the spawning season. E2 at 4.0 mg completely suppressed spermiation, while lower doses of E2 (0.25 and 1.0 mg) delayed spermatogenesis but increased the number of spermiating fish and spermiation volume. Sperm concentrations were similar in a spermiating black porgy. At 10 months and older, gonads in all the groups except E2 (4.0-mg)-treated fish underwent an intensive spermatogenesis while spermatids were not observed until 11 and 12 months in the 0.25- and 1.0-mg E2 groups, respectively. Primary oocytes appeared in the 10- and 11-month-old gonads in testicular tissue of the 1.0- and 4.0-mg E2 groups. After 5 months of 4-mg E2 treatment, testicular tissue regressed and ovarian tissue with primary oocytes developed. Elevated levels of plasma E2 were observed only in the 4.0-mg E2 group while low levels of E2 and testosterone (T) were observed in the control and other E2-treated groups. Significantly higher levels of plasma 11-ketotestosterone (11-KT) were observed in the 0.25- and 1.0-mg E2-treated groups during the spawning season. Plasma vitellogenin levels showed a dose-dependent effect of E2 treatment. The present data suggest that exogenous E2 could stimulate the development of either testicular or ovarian tissues, depending on the dosage of E2, Plasma 11-KT but not T concentrations closely correlate with testicular development and spermiation in black porgy.
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