Abstract
Black porgy,Acanthopagrus schlegeli Bleeker,a marine protandrous hermaphrodite,is functional male for the first 2 years of life but begin to sexually change to female after thethird year.Testicular tissue and ovarian tissue was separated by connective tissue in thebisexual gonad.This sex pattern provides a unique model to study the endocrinemechanism of sex change in fish.The annual profiles of plasma estradiol,vitellogeninand 11-ketotestosterone concentrations in males were significantly different from those inthe 3-year-old females.Significantly high levels of plasma estradiol during the prespawning/spawning season and low levels of plasma 11-ketotestosterone during the spawningseason were observed in the inversing females.No difference of plasma testosteronelevels was observed in males and females.Oral administration of estradiol stimulatedhigh levels of gonadal aromatase activity,plasma luteinizing hormone levels and sexchange in the 2-year-old fish.Oral administration with aromatase inhibitors for a yearfurther blocked the natural sex change in 3-year-old black porgy and all fish becamefunctional male with spermiation.Transcripts of estrogen receptor and androgen receptorin the ovarian tissue of bisexual gonad are significantly less expressed than those in thebisexual testicular tissue on the basis of a real time-PCR.Estrogen receptor transcriptsare much higher in the vitellogenic ovary than those in the bisexual ovarian tissue.It isconcluded that estradiol,aromatase and steroid receptors in the gonadal tissue play animportant role in the natural and controlled sex change in black porgy.
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