Effect of Diethylstilbestrol and Norethindrone on Sex Ratio and Body Indices of Common Carp, Cyprinus carpio (Linn.)

A synthetic estrogen diethylstilbestrol (DES) and a synthetic androgen, norethindrone (NE) were evaluated for their efficacy on sex ratio and body indices of common carp, Cyprinus carpio (Cyprinidae). Five-day-old fry of common carp were fed diets incorporated with DES at 400, 500 and 600mg kg^-1 diet for 30 days in circular fiberglass tanks; this was followed by 120 days rearing on hormone free-diet in fertilized concrete tanks. All the treatments significantly altered the sex ratio; DES at 400mg kg^-1 was found to be the best as it produced the lowest percentage of males (7.7). At 400 and 500mg kg^-1 the production of females was significantly higher. Interestingly, the percentage of intersex fish increased as the dosage of DES increased. The control group had 60.6% males and 39.4% females. In another experiment, NE fed at 50 mg kg^-1 diet to different age groups (10-, 20- and 30-d-old) of common carp for 50 days, produced 100% male population in all the groups. In control, 52-55.55% males and 44.5-48% females were observed. This is the first report on the complete masculinization of common carp with NE. In both the experiments, the average final weights of common carp varied slightly depending on the survival, which was generally good. In general, DES and NE treatments resulted in a slight variation in the gonadosomatic index and hepatosomatic index of common carp. Hormone treatment resulted in lower viscerosomatic index in all the groups excepting 20- and 30-d-old fry. The condition factor of females was higher in all the hormone treated fish, while the values were lower in DES-treated males than that of control. The histological examination of gonads indicated the presence of males, females, sterile and intersex fish in all the DES treated fish, whereas it revealed the presence of only males in all the NE-treated common carp. The oral administration of the gonadal hormones did not significantly affect the proximate composition of the muscle of common carp. The benefits of stocking grow out ponds with monosex or sterile carp fry are also discussed.