Effect of 17-α-methyl testosterone on the sex reversal of rainbow trout (Oncorhynchus mykiss)

This study was conducted to reverse female trout to male (XX male) by oral administration of 17-alpha-methyl testosterone. For this purpose, 12,000 larvae of rainbow trout were fed from the beginning of active feeding with diets containing 0 (control), 0.5, 1, 1.5 and 2 mg 17-alpha-methyl testosterone per kg of feed for 60 days. The growth performance and survival were evaluated during this period. In addition, the treated fish were fed with hormone-free commercial diet for 18 months until their sex glands had grown. The sex reversal of fish was performed by sampling from 120 numbers of fry (2g mean weight) fin tails, designing specific primers and PCR assay. The results of growth showed that there was no significant difference in growth parameters among treatments (P>0.05). Fish treated with the hormone had lower survival rate (82.1±1.1%) compared to the control group (P<0.05). By necropsy and direct observation of the sexual organs of the breeders, the ratio of female to male sex reversal was increased by increasing the concentration of the hormone from 0.5 to 2 mg/kg in the diets and the best efficiency was obtained in 2 mg/kg of 17-alpha-methyl testosterone (P<0.05). The results of this study showed that the highest ratio of male XX breeders (96.0±1.0%) was observed in the fish fed with alpha methyl testosterone at 2 mg/kg of feed. Also, the PCR test had the specificity to identify the sex reversal of rainbow trout fry as a non-invasive method.