Sex Inversion of Sexually Immature Honeycomb Grouper (Epinephelus merra) by Aromatase Inhibitor

Abstract

The honeycomb grouper, Epinephelus merra , is a protogynous hermaphrodite fish. Sex steroid hormones play key roles in sex change of this species. A significant drop in endogenous estradiol-17β β β β (E2) levels alone triggers female-to-male sex change, and the subsequent elevation of 11-ketotestosterone (11KT) levels correlates with the progression of spermatogenesis. To elucidate the role of an androgen in sex change, we attempted to induce female-to-male sex change by exogenous 11KT treatments. The 75-day 11KT treatment caused 100% masculinization of pre-spawning females. Ovaries of the control (vehicle-treated) fish had oocytes at various stages of oogenesis, while the gonads of the 11KT-treated fish had transformed into testes; these contained spermatogenic germ cells at various stages, including an accumulation of spermatozoa in the sperm duct. In the sex-changed fish, plasma levels of E2 were significantly low, while both testosterone (T) and 11KT were significantly increased. Our results suggest that 11KT plays an important role in sex change in the honeycomb grouper. Whether the mechanism of 11KT-induced female-to-male sex change acts through direct stimulation of spermatogenesis in the ovary or via the inhibition of estrogen synthesis remains to be clarified.

Sexual development and reproductive pattern of the Mutton hamlet, Alphestes afer (Teleostei: Epinephelidae): a dyandric, hermaphroditic reef fish

“…This process, called juvenile sex inversion, has been previously reported for sparids (Francis & Pankhurst, 1988) as well as for serranids (Ferreira, 1995;Bhandari et al, 2004;Liu & Sadovy, 2004). These males function only as one sex during their lifetime and are not functional sex-changers according to Sadovy & Shapiro (1987).…”

Profiling neuroendocrine gene expression changes following fadrozole-induced estrogen decline in the female goldfish

“…Histology was used to determine the effect of fadrozole on female goldfish since effects on gonad development have been observed in other fish (2,4,15,38,45) and frog species (41). In the female control goldfish, the oocytes were evident in the cortical alveolar/vitellogenic stages (Fig.…”

“…Moreover, in contrast to mammals where aromatase and nER are commonly expressed in neurons, current studies in fish and birds strongly suggest that AroB is exclusively expressed in radial glial cells and nER is mostly expressed in neurons (16,43). Thus, the local production of glial estrogen and signaling to neurons is an important interaction between these cell types that has fundamental implications for neurogenesis, neuronal regeneration, neuroprotection, and neuroendocrine function (16,19,37).Profiling the physiological effects of fadrozole, a reversible competitive inhibitor of aromatase, has been used successfully in studies investigating estrogen action in fish (2,4,15,38,45,69), frog (41), and rodent (23) models. By inhibiting aromatase activity, fadrozole decreases serum E2 levels (2, 4), impairs gonadal development (2), and potentially induces sex reversal in fish (4, 15, 69).…”

“…Profiling the physiological effects of fadrozole, a reversible competitive inhibitor of aromatase, has been used successfully in studies investigating estrogen action in fish (2,4,15,38,45,69), frog (41), and rodent (23) models. By inhibiting aromatase activity, fadrozole decreases serum E2 levels (2,4), impairs gonadal development (2), and potentially induces sex reversal in fish (4,15,69).…”

“…By inhibiting aromatase activity, fadrozole decreases serum E2 levels (2,4), impairs gonadal development (2), and potentially induces sex reversal in fish (4,15,69). However, the associated gene expression changes caused by fadrozoleinduced E2 decline in neuroendocrine systems are still largely unknown.…”