The effect of Letrozole and Letrozole-Chitosan nanoparticles on masculinization of Rainbow trout larvae (Oncorhynchus mykiss)

This study aimed to investigate the efficiency of conjugating chitosan nanoparticles to letrozole (LET) on masculinization of rainbow trout larvae, Oncorhynchus mykiss. For this purpose, two treatments of LET, 1.5 and 3 mg/kg food, and two treatments of letrozole-chitosan nanoparticles (LET-CS), 0.5 and 1.5 mg/kg were performed with a control group. Treatments began immediately after active larval swimming and continued for 60 days. The results showed that the amount of testosterone during the trial increased significantly (p<0.05), so that the highest amount of testosterone was observed in 3 mg/kg LET and 1.5 mg/kg LET-CS. However, estradiol was untraceable in all treatments. About 66.6, 73.33, 73.33, 76.66 and 43.33% males were observed in 1.5 mg/kg LET, 3 mg/kg LET, 0.5 mg/kg LET-CS, 1.5 mg/kg LET-CS and control, respectively. Despite the drug dosage in LET-CS treatments was half that of LET treatments, the sex ratio did not change among treatments (p >= 0.05), which showed a positive effect of CS in effectiveness of LET. In general, it can be stated that using CS for the administration of LET could be effective in inhibiting the production of estradiol, increasing the amount of testosterone, and thus changing the sex ratio of rainbow trout.