Harmonic factors affecting gonadal sex differentiation in fish

1. Using as material the offspring of white females (XrXr) mated with heterozygous orange-red males (XrYzR) of the medaka (Oryzias latipes), an oviparous cyprinodont, previous experiments are extended. 2. Functional sex-reversal in genetic males (XY) can be induced under the influence of estrone, estradiol, and stilbestrol and that in genetic females (XX) by means of methyltestosterone, testosterone propionate, and androsterone, administered by oral route from hatching time (indifferent gonad) to certain juvenile stage (12 mm). 3. Progesterone and nonsex-hormonic cortico-steroids (DOCA and cortisone acetate), on the other hand, give only negative results in reversing sex differentiation even though they are administered in large quantities. Specific action of estrogens and androgens as gyno-inductor and andro-inductor, respectively, are stressed. 4. The critical stage of gonadal sex differentiation seems to be restricted from 6 to 11 mm stage (caudal included). 5. Evidence is presented to demonstrate that the induced sex-reversal of either genetic male (XY) or genetic female (XX) is permanent.