Masculinization of Poecilia reticulata by dietary administration of synthetic or natural androgen to gravid females

Abstract

The masculinizing effects of three synthetic androgens, 19-nor-ethynyltestosterone (100-500 mg/kg food), 17β-ethynyltestosterone (100-500 mg/kg food), 9(11)-dimethyltestosterone (100-400 mg/kg food) and a natural steroid, androstenedione (100-400 mg/kg food), were investigated in the guppy, Poecilia reticulata. Androgens were administered orally to gravid females for a period of 5-24 days, prior to parturition. All the resulting progeny were sampled to examine the sex ratio. Essentially all male populations were produced following treatment with androstenedione, 19-nor-ethynyltestosterone, and 17α-ethynyltestosterone at doses of 200, 300 and 500 mg/kg food, respectively. 9(11)-Dimethyltestosterone was associated with incomplete sex reversal and, at the highest dose used (400 mg/kg diet), increased mortality. Sex reversal of genetic females was confirmed by subsequent progeny testing, 8 of 34 individuals generating all female populations when crossed with normal females. Androstenedione was the most potent androgen that ensured sex reversal with maximum survival and functional equality.