Role of Follicle-Stimulating Hormone and Androgens on the Sexual Inversion of Sevenband Grouper Epinephelus septemfasciatus

Abstract

This study was designed to characterize the amount of androgen implant and the time period necessary to cause sexual inversion in sevenband grouper Epinephelus septemfasciatus and to determine whether administration of follicle-stimulating hormone (FSH) with or without androgens had any effect on the sexual state of this species. Seventy-two fish were treated with 10 μg of recombinant FSH/kg body weight (BW) or saline control in cocoa butter. Two days later, cocoa butter and α-cellulose pellet implants of control, 0.1 mg of low-androgen mixture (LoAN)/kg BW, or 5 mg of high-androgen mixture (HiAN)/kg BW were injected into the same fish. Fish were sampled after 3 and 5 weeks. Gonadosomatic indices (GSIs) at 3 weeks for FSH, HiAN, and FSH+HiAN treatment groups were significantly lower than the control values. At 5 weeks, no significant difference was observed, although the GSIs for HiAN treatment groups were lowest at both sampling points. The highest GSI values recorded were in the FSH-only treatment group at 5 weeks. All the controls remained in the immature female state throughout the study. High-dose androgen levels caused sexual transition of gonadal tissue at 3 weeks with spermatocytes present in all individuals. At 5 weeks, all individuals in the HiAN treatment group had complete inversion to male gonad, and sperm sinus development occurred in four individuals. However, incomplete sexual inversion was observed in the FSH+HiAN treatment groups with some ovarian tissue persisting even at 5 weeks. Exogenous FSH treatment alone appears to stimulate ovarian growth in the postspawning period. The 3-week period of sexual transition in this study is one of the shortest time periods recorded for grouper sexual inversion. This may be due to androgen treatment in the postspawning period, the proposed period of natural sex change in several grouper species.