Brief Exposure of Embryos to Steroids or Aromatase Inhibitor Induces Sex Reversal in Nile Tilapia (Oreochromis niloticus)

This study aimed to develop sex reversal procedures targeting the embryonic period as tools to study the early steps of sex differentiation in Nile tilapia with XX, XY, and YY sexual genotypes. XX eggs were exposed to masculinizing treatments with androgens (17-methyltestosterone, 11-ketotestosterone) or aromatase inhibitor (Fadrozole), whereas XY and YY eggs were subjected to feminizing treatments with estrogen analog (17-ethynylestradiol). All treatments consisted of a single or double 4-hr immersion applied between 1 and 36hour post-fertilization (hpf). Concentrations of active substances were 1000 or 2000g l(-1) in XX and XY, and 2000 or 6500g l(-1) in YY. Masculinizing treatments of XX embryos achieved a maximal sex reversal rate of 10% with an exposure at 24hpf to 1000g l(-1) of 11-ketotestosterone or to 2000g l(-1) of Fadrozole. Feminization of XY embryos was more efficient and induced up to 91% sex reversal with an exposure to 2000g l(-1) of 17-ethynylestradiol. Interestingly, similar treatments failed to reverse YY fish to females, suggesting either that a sex determinant linked to the Y chromosome prevents the female pathway when present in two copies, or that a gene present on the X chromosome is needed for the development of a female phenotype. J. Exp. Zool. 323A: 31-38, 2015. (c) 2014 Wiley Periodicals, Inc.