Production of neo-males from gynogenetic yellow drum through 17α-methyltestosterone immersion and subsequent application for the establishment of all-female populations

Mono-sex culture of yellow drum (Nibea albiflora) provides economic advantages in industry because of the superior growth of females relative to males. Sex-reversal of genetic females (XX) to produce neo-males is an indispensable step toward establishing all-female populations. To achieve this goal, gynogenetic yellow drum at an undifferentiated sex stage (total length, 1.63 ± 0.16 cm) were immersed in 17α-methyltestosterone (17α-MT) for 2 h/day from 30 to 90 dph (60 days), producing sex-reversed fish (neo-males). All the four 17α-MT concentrations tested (0.2, 2, 10, 50 μg/L) drove the development of testes, evidenced by histological observations of the gonads. The masculinization of gynogenetic yellow drum was also demonstrated by the expression patterns of two sex-specific genes, dmrt1 and cyp19a1a: the gonads of 17α-MT-treated fish exclusively expressed male-specific dmrt1 with no expression of female-specific cyp19a1a. Specifically, treatment with 0.2 μg/L 17α-MT yielded complete sex-reversed fish without any abnormalities in gonadal development, and the growth of neo-males was not significantly different to that of controls during the treatment period. However, testicular abnormalities were observed in groups treated with higher 17α-MT concentrations, with a trend for more abnormalities with increasing 17α-MT concentrations, and the growth of 17α-MT-treated fish was retarded at these higher 17α-MT concentrations. These results indicated that high concentrations of 17α-MT had adverse effects on growth and gonadal development, and the most efficient concentration tested for producing neo-males was 0.2 μg/L. Furthermore, crossing of gynogenetic sex-reversed males with normal females produced 100% females, demonstrating the potential efficiency of this protocol for reversing the sex of yellow drum and establishing large-scale production of all-female populations.