Masculinization and physiological responses of rosy barb, Pethia conchonius to combined hormonal treatment

The ornamental fish industry has the potential to enhance profitability through the development of high-value, high-demand species, where value and demand are influenced by factors such as size, coloration, and sex. The aim of this research is to evaluate the combination of 17α-methyltestosterone (MT) and letrozole (LET), an aromatase inhibitor (AI), in inducing masculinization in the rosy barb, Pethia conchonius. The fry of the rosy barb was acclimated to the gel-based diet for 5 days prior to beginning a 90-day experiment in a closed environment. The experimental design included a control (without AI) group and three treatment groups: T1 (M_12.5+L₁₅₀), T2 (M₂₅ + L₁₀₀), and T3 (M_37.5+L₅₀) mg/kg feed. The highest percentage of males (86.90 ± 0.59%) was recorded in the M_37.5+L₅₀ mg/kg group after 90 days, which was significantly different from the other groups. The histological sections showed suppressed ovarian development with atretic oocytes, while testicular development remained unaffected. Additionally, the concentration of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST), and glutathione peroxidase (GPX), were significantly increased in the control group compared to treated groups (P < 0.05). Instrumental color analysis on the basis of L*, a*, and b* values showed fed gel-based feed with M_37.5+L₅₀ mg/kg had significantly more vibrant color than those in the control groups (p < 0.05). Digestive enzyme activity, such as protein (70 ± 0.52), protease (0.054 ± 0.001), lipase (11.16 ± 0.28), and amylase (8.80 ± 0.78), varied among treatment and control groups. These findings suggest that incorporating AI at a concentration of 37.5 mg/kg + L50 mg/kg within a gel-based feed is a promising approach for masculinizing rosy barbs without significantly impacting their growth, color, or antioxidant activity. This approach holds significant potential for the ornamental fish industry by enabling the production of all-male populations.