The optimum dose and period of 17α-methyltestosterone immersion on masculinization of red tilapia (Oreochromis spp.)

This study was carried out to examine the effect of combining factors for immersion technique on masculinization of red tilapia (Oreochromis spp.). Three selected doses (1000, 1,500, and 2000 μg/L) of 17α-methyltestosterone (17 MT) immersion, 2 exposure times (3 and 6 h) once or twice a week, and interaction of these factors were tested. A total of 12 treatment combinations under 3 × 2 × 2 factorial experiments in randomized complete block design were conducted to compare with the negative control group (no 17 MT-treated) and positive control group (17 MT-treated feed administration). One hundred red tilapia larvae (14 days post-hatch) were randomly allocated in each treatment and were operated in a 10-L glass jar for 21 days. At the end of the treatment regime, the survival rate was determined. Then, fish were raised in a 150-L glass tank using normal commercial feed for 2 months and sex ratios were determined via the gonad squash technique. None of the immersion treatments tested resulted in a statistically significant (p > 0.05) decrease in survival rate. All 17 MT-treated groups produced progenies with a significantly higher (p < 0.001) proportion of males than the predicted 1:1 sex ratio. Influences of some factor combinations in the masculinization of red tilapia were observed. The male ratio was significantly affected by the dose-period and dose-frequency treatments (p < 0.05). The highest male proportion (95.33% ± 0.58%) was recorded at 1000 μg/L of 17 MT for 6 h once a week which was significantly higher (p < 0.05) than other groups. The production cost of the best group was the cheapest (THB0.0066/fish) and decreased from the traditional procedure by about 10.81%. Therefore, this technique could be implemented for decreasing cost and operating process in commercial tilapia farms.