Evidence that estrogen regulates the sex change of honeycomb grouper (Epinephelus merra), a protogynous hermaphrodite fish.

Circulating estradiol-17beta (E2) levels decrease precipitously during female to male (protogynous) sex change in fish. Whether this drop in E2 levels is a cause or consequence of sex change is still largely unknown. The present study treated adult female honeycomb groupers (Epinephelus merra) with aromatase inhibitor (AI, Fadrozole), either alone or in combination with E2, to investigate the role of estrogen in protogynous sex change. Control fish had ovaries undergoing active vitellogenesis; the gonads of AI-treated fish had already developed into testes, which produced sperm capable of fertilization. In contrast, co-treatment of fish with E2 completely blocked AI-induced sex reversal. AI treatment significantly reduced circulating levels of E2, whereas the addition of E2 to AI prevented the loss. The plasma androgen (testosterone and 11-ketotestosterone) levels were increased in the AI-treated fish, while the levels in the E2-supplemented fish were low compared to controls. Present results show that E2 plays an important role in maintaining female sex of hermaphrodite fishes, and that the inhibition of E2 synthesis causes oocyte degeneration leading to testicular differentiation in the ovary. Copyright 2005 Wiley-Liss, Inc.