Production of a high percentage of male offspring with 17α-ethynylestradiol sex-reversed Oreochromis aureus. I. Estrogen sex-reversal and production of F2 pseudofemales

Abstract

This study aims at developing a production process of male monosex populations of tilapia without the use of steroids. The sex-reversal of O. aureus (male genotype, ZZ; female genotype, ZW) with an estrogen treatment produces pseudofemales with a male genotype (ZZ). Crossing these fish with normal males (ZZ) gives, in theory, 100% male offspring. The objective of this study was to develop this technique for mass production of pseudofemale O. aureus producing a high percentage of male offspring. Batches of 250 O. aureus fry were submitted during a 40-day period to 17α-ethynylestradiol treatments of 100, 150 and 200 mg · kg −1 of food. We obtained 93 to 98% females in the treated groups in comparison with 53% females in the control group. Females randomly taken from the treated groups were crossed with normal males. Out of 64 fish tested, 30 gave progenies with a high percentage of males (68 to 100%) and were considered as pseudofemales. Crosses were repeated ( n = 2–5) to test the sex ratio stability in successive progenies (variation from 0 to 16.4% of the male ratio). Fry from pseudofemales producing only 100% male progenies were submitted to a 17α-ethynylestradiol treatment of 150 mg · kg −1 of food to obtain F2 pseudofemales. The results of the sex-reversal were variable and fluctuated between 18 and 95% of females. After the elimination of the males, we obtained 725 sexually mature F2 pseudofemales. Tests of the progeny of 6 F2 pseudofemales gave 97.5 to 100% of males and showed the heritability of the high percentage male offspring feature of the selected fish. These results confirm the possibility of multiplication of the pseudofemale stock (F2) to obtain, on a large scale, all-male progenies. Although it would be difficult to obtain only 100% male offspring, this method has the advantage, when compared to the classical sex-reversal process with 17α-methyltestosterone, of producing high percentage male progenies without the use of steroid treatment.