| Summary: | 碩士 === 國立海洋大學 === 水產養殖學系 === 87 === AbstrateThe objestives of the present study were to investigate the levels of sex steroids, gonadotropin II (GTH II) and aromatase in the protandrous black porgy (Acanthopagrus schlegeli) during the prespawning and spawning season.Plasma GTH II levels were the highest in October (prespawning) and December (spawning season) in 3-year-old fish. There is no different profiles of plasma GTH II levels in mature males and naturally reversed females. The plasma estradiol-17 (E2) and vitellogenin levels were higher in naturally reversed females than in males during the spawning season, but low levels of E2 and vitellogenin in non-spawning season were observed in both males and females. Two-year-old black porgy were implanted with silastic tubes filled with two kinds of aromatase inhibitors, 1,4,6-androstatriene-3,17-dione (ATD) and 4-benzonitrile monohydrochloride (fadrozole) in March. Significantly lower aromatase activity was observed in forbrain, midbrain and hindbrain but with no difference in gonad in October. ATD is more effective than fadrozole on the suppression of brain aromatase activity. Treatment with fadrozole but not ATD could increase plasma GTH II levels. Injection of E2 and testosterone but not 5-dihydrotestosterone could stimulate aromatase activity in forebrain, midbrain and hindbrain. Lower aromatase activity in the forebrain, midbrain and hindbrain after the injection with ATD and ATD + testosterone.Injection of E2, testosterone and ATD could stimulate plasma GTH II levels. The studies concluded that higher plasma E2 and vitellogenin but not GTH II levels were correlated to the occurrence of sex reversal. E2 had both positive and negative feedback effects in GTH II levels of black porgy.
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