17 beta-Estradiol, but not testosterone stimulates gonadotropin II concentrations in the protandrous black porgy, Acanthopagrus schlegeli Bleeker

The objective of the present study was to investigate the in vivo effects o f different doses of 17 beta-estradiol (E-2) and testosterone (T) on the le vels of plasma and pituitary gonadotropin II (GTH II) in 2-year-old black p orgy, Acanthopagrus schlegeli, during the spawning season. Male fish were d istributed among 7 groups (n = 49), control, E(2)or T (with 3 doses, 2.4 ng , 72 ng and 2.2 mu g g(-1) body weight). Fish were injected with the respec tive vehicle or different doses of E-2 or T on days 1 and 14. Plasma E-2 le vels were significantly increased in the 72 ng E-2 group on days 8 and 14. Plasma vitellogenin levels were significantly higher in the 72 ng E-2 group on days 14 and 20, and 2.2 mu g E-2 group on days 8, 14 and 20 than those in the control group. Plasma GTH II concentrations were significantly highe r in the 2.2 mu g E-2 group than in the control and other E-2 groups on day s 8, 14 and 20. Pituitary GTH II contents was significantly higher in the 7 .2 ng E-2 group compared to the control and other E-2 groups on day 20. Pla sma GTH II concentrations were similar in the control and all the T groups on days 8, 14 and 20. None of the doses of T treatment stimulated pituitary GTH II content on day 20, although plasma vitellogenin levels were elevate d. It is concluded that GTH II synthesis and secretion in black porgy is st imulated by an estrogen-specific effect.