Seasonal cycles of gonadal development and plasma sex steroid levels in Epinephelus morio, a protogynous grouper in the eastern Gulf of Mexico

Abstract

In a field population of the protogynous red grouper Epinephelus morio in the eastern Gulf of Mexico, females with oocytes at all stages of development were collected during the spawning season suggesting that several batches of oocytes may be released over the spawning period. Plasma oestradiol (E 2 ) levels were highest in ripe females whose gonads contained both cortical alveoli and vitellogenic oocytes during the breeding season. Males were still spermiating as late as August, although levels of androgens 11-ketotestosterone (11-KT) and testosterone (T) had declined from their peaks in March. A few red grouper with either perinucleolar or cortical alveoli stage oocytes were undergoing sex change both during and after the spawning period. Low levels of E 2 , T and 11-KT were detected in transitionals. Proliferation of male tissue was not restricted to any specific area of the gonad but occurred in pockets within the ovarian lumen. The sequence of an increase in gonial cells along the periphery of the lamellae, increase in interstitial tissue, degradation of female elements, and formation of a sperm duct seemed to be concurrent with spermatocyte proliferation and the process of preparing the gonad to function as a testis. 1998 The Fisheries Society of the British Isles

Molecular mechanisms underlying sex change in hermaphroditic groupers

“…Previous studies have focused mainly on the descriptions of gonad ultrastructure and histology at different developmental stages (Smith 1965;Moe 1969;Tan and Tan 1974;Bruslé and Bruslé 1975;Kuo et al 1988;Bruslé-Sicard et al 1992;Johnson et al 1998;Marino et al 2001;Bhandari et al 2003). Marino et al (2001) have depicted gonad morphology of the dusky grouper (E. marginatus) by the histological observation of 405 individuals from the Pelagie Islands in the Mediterranean Sea.…”

“…In males, 11-KT, teleost-specific androgen, is considered a principal androgen in teleostean fish, and it plays a central role in sexual maturation, development of secondary sexual characteristics and reproductive behaviour (Miura et al 1991;Borg 1994). In many sexchanging fish, the levels of circulating 11-KT have been reported to increase with the progression of sex change (Nakamura et al 1989;Johnson et al 1998;Kroon and Liley 2000;Bhandari et al 2003), and exogenous 11-KT treatment can induce sex reversal (Kroon and Liley 2000;Yeh et al 2003). It was found that the androgen-producing sites exist in the ovary of honeycomb grouper (Alam et al 2005) and that naturally occurring sex change is accompanied by significant increases in the size of androgen-producing cells and production of androgen by the gonads .…”

Induction of Female-to–male Sex Change in the Honeycomb Grouper (Epinephelus merra) by 11-ketotestosterone Treatments

“…In many sex-changing fish, the levels of circulating 11KT have been reported to increase with the progression of sex change (Nakamura et al ., 1989;Johnson et al , 1998;Kroon and Liley, 2000;Bhandari et al , 2003;Perry and Grober, 2003), and exogenous 11KT treatments have been shown to induce female-to-male sex change (Kroon and Liley, 2000;Yeh et al , 2003). Our previous studies suggest that a drop in E2 levels alone is the key to the onset of sex change in honeycomb grouper, and that increasing testosterone (T) and 11KT levels following gonadal transformation could be stimulatory to male germ-cell proliferation and differentiation in the ovary.…”

Fish Resources of the Gulf of Mexico

“…Although abundance of red grouper has changed substantially over time, the sex ratio of the population has not changed greatly since 1975 (Coleman et al 1996). Peak spawning occurs in late spring, during March and May in the eastern Gulf of Mexico, but spawning may occur from January through June in the Gulf of Mexico and Caribbean Sea (Tables 9.12 and 9.13) (Johnson et al 1998). Red grouper are indeterminate batch spawners (Johnson et al 1998;Collins et al 2002).…”

“…Peak spawning occurs in late spring, during March and May in the eastern Gulf of Mexico, but spawning may occur from January through June in the Gulf of Mexico and Caribbean Sea (Tables 9.12 and 9.13) (Johnson et al 1998). Red grouper are indeterminate batch spawners (Johnson et al 1998;Collins et al 2002). Fecundity is related to size and ranges from 312,000 to 5,735,700 eggs.…”