下視丘、 腦下腺和生殖腺所分泌的神經激素及性類固醇激素與性轉換有
密切相關， 而性轉換時性類固醇激素對中樞神經內分泌系統的作用機轉
，尚未被充分的探討。 本研究目的：藉由人為誘導黑鯛性轉換的過程，
了解黑鯛生殖神經內分泌系統 ( 下視丘 - 腦下腺 ) 在性轉換時對於性
類固醇激素負迴饋作用的敏感度是否有改變。 本實驗以二年齡黑鯛為材
料，以腹腔包埋雌二醇 (17 β -estradiol；E2) 或睪固酮
(testosterone； T)， 計算生殖腺指數 (gonadosomatic index
； GSI)、 肝指數 (hepatosomatic index)、卵巢面積比例及卵細胞
組成分佈。並測定血清中 E2、 T、 促性腺激素 (gonadotropin；
GTH) 及下視丘部位性釋素 (gonadotropin releasing hormone；GnRH)
的濃度變化。實驗結果如下： ( 一 ) 在切除性腺及包埋性類固醇 (GNX+
steroid) 的動物模式中， 包埋 E2 組在生殖季時血清中 GTH 分泌量有
上升趨勢。而包埋 T 組血清中 GTH分泌量從生殖準備期到生殖季無顯著
變化。且包埋 E2 組下視丘部位 GnRH濃度顯著高於包埋 T 組。 (
二 ) 在不切除性腺及包埋性類固醇 (intact+steroid) 的動物模式中
， 控制組血清中 GTH 分泌量從生殖準備期到生殖季呈不規則變化，在生
殖季時 GSI 值顯著增加，卵巢面積所佔比例顯著下降，卵細胞發育停留
在初級卵細胞期， 有 93 ％黑鯛發育為成熟雄魚。包埋 E2 組在生殖季
時血清中 GTH 分泌量有顯著增加，且生殖腺以卵巢組織佔絕大多數，
有 40 ％黑鯛性轉換為成熟雌魚，有大量的卵細胞發育至卵黃球期， 且
無成熟雄魚產生。 包埋 T 組在生殖季時血清中 GTH分泌量無顯著變化
， 生殖腺以卵巢組織為主，卵細胞發育停留在初級卵細胞期或卵黃胞期
，亦無成熟雄魚產生。 下視丘部位 GnRH 濃度在控制組和包埋 E2、T 組
都發現在生殖季前顯著較低，其餘時間則無明顯變化。綜合以上結論，
在 GNX+steroid 的動物模式中，明顯觀察到在生殖季時，中樞神經系統
對於 E2 負迴饋作用的敏感度降低，使的血清中 GTH 分泌量有上升趨勢
。 在 intact+steroid 的動物模式中，生殖季時亦可觀察到相同的現象
， 且此時包埋 E2 組較控制組有更高比例的黑鯛性轉換為成熟雌魚，這
些現象同樣的說明了黑鯛在性轉換過程中，下視丘 - 腦下腺對 E2 負迴
饋作用的敏感度發生了改變，而促使腦下腺釋放於血清中的 GTH 量增加
。

Similarly, sex reversal in protandrous black porgy
(Acanthopagrus schlegeli) is also a dramatic change of the
physiological condition. This change may also include the
phenomenon that hypothalamo-hypophyseal axis responds to
the steroid feedback differently. The objective of this study
is to examine the serum gonadotropin (GTH) level as an index to
the change of steroid sensitivity in the neuroendocrine system
during the course of induced sex reversal in two-year-old
black porgy. Firstly, we compare effects of estrogen and
androgen on the GTH secretion in the gonad-intact fish.
Silastic tube filled with testosterone (T) or 17 β
-estradiol (E2) were implanted intraperitonealy.
Significantly higher concentration of serum GTH was only
observed in the E2 treated group during spawning season as
compared to recrudescent period. Th ere were 40 ％ of black
porgy developed into functional females and no functional
male were found in E2 treated group. In contrast, only 7 ％ of
fish turned into functional females, while the rest
remained in the functional male phase during the spawning
season in the control group. Secondly, endogenous gonadal
steroids were removed by gonadoectomy and the fish were
treated with constant release of androgen and estrogen by
Silastic implant. Higher concentration of serum GTH was also
observed in the E2 treate d group during spawning season as
compared to prespawning season. Significantly higher
concentrations of hypothalamic GnRH were observed in the E2
treated group as compared to the T treated group during
spawning season. These results suggest that the