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

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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.