RESUMO
Norethindrone(NE) was evaluated for its efficacy on alteration of sex ratio of P. reticulata. Either the young fry or the brooders and the resultant fry were fed a commercial diet incorporated with NE at 0, 25, 50, 75 and 100 mg kg-1 diet (ppm) for 30-40 d in rectangular glass aquaria; this was followed by 40-60 d rearing on NE-free diet in out-door concrete tanks. In general, the androgen treatment altered sex ratio, leading to the production of a dose dependent increase in the percentage of males. The oral administration of the steroid at 75 ppm for 40 d or 100 ppmfor 30 or 40 d to first feeding fry, yielded 100% males. On the other hand, NE administration to brooders before parturition and the resultant fry also produced an all-male population of guppy. The sex ratio of the untreated control was almost 1:1. The survival of fish in all the trials was high, ranging between 67 and 100%. Mating masculinized males (“XX” male) with normal female resulted in an all-female progeny, while crossing normal male (XY) from treatment groups with normal female sired normal sex ratio (1:1), elucidating XX-XY sex determination system in the guppy.