Research Article: Inhibition of aromatase activity in rainbow trout (Oncorhynchus mykiss) larvae to produce neomale fish through immersion with letrozole

Monosex female rainbow trout can be produced by using neomale broodstock. This study aimed to administer Letrozole, an aromatase enzyme inhibitor, in the sexual differentiation process of rainbow trout through the immersion method. Accordingly, three treatments of ۲۵۰ μg/L (LET۲۵۰), ۵۰۰ μg/L (LET۵۰۰) and ۱۰۰۰ μg/L (LET۱۰۰۰) of letrozole were used. The results of the sex ratio analysis showed a positive effect of the treatments and a significant difference compared to the control group (p< ۰.۰۵). The best results were obtained for treatment LET۱۰۰۰ with ۸۸ percent of male specimens. The highest concentrations of testosterone and aromatase were measured in treatment LET۱۰۰۰, at ۰.۲۸۱±۰.۰۸۲ ng/g and ۰.۷۲±۰.۳۱ ng/g, respectively. This treatment also exhibited the lowest concentration of estradiol. The results obtained in this study show the positive effect of letrozole in inhibiting aromatization, which leads to the production of fish with a male phenotype in the drug-treated population. Regarding survival, the use of letrozole, like testosterone, increased mortality in the experimental treatments. In terms of growth rate, the study's results on the treatments' weight showed that the use of letrozole increased growth in the experimental treatments. Regarding morphological malformation, treatment LET۱۰۰۰ with deformed larvae had the highest rate of deformity among the experimental treatments, but was not significantly different from the rate recorded for the control group (p≥۰.۰۵).  Based on the results obtained, it can be stated that letrozole is an effective drug in changing the sex of rainbow trout and can be used as a substitute for methyltestosterone.

کلیدواژه ها:

Rainbow trout ، Neomale ، Letrozole ، Masculinization ، Aromatase activity