The objective of this study was to determine the efficacy of two procedures i.e. feeding and immersion followed by feeding, for masculinizing Blue Hap. Two experiments (experiments I and II) were conducted. In experiment I, feeding hormonal treatment was applied on post-yolk sac stage fry (10 days after fertilization at 27ºC). Dosages of 30mg (group A) and 60mg (group B) of 17α-methyltestosterone per kg of food were used during 60-day periods (40 fry per treatment). The control group i.e. group C, received no hormone. In experiment II, one day post hatching larvae were exposed to an immersion treatment in 17α-methyltestosterone at 1000 μg/l up to 2 h (16 larvae per treatment). Later, at the first day of post-yolk sac stage, the treatment was followed by oral procedure which was divided in 2 groups: group D and group E. In group D, 30 mg 17α-Methyltestosterone per kg of food was used during a 60-day period. In group E, fry received 60 mg of hormone per kg of food during the same period. The control group i.e. group F, did not receive any hormone. Change in sex proportion within each experiment as well as between experiments was analyzed by chi-square test (p<0.05). In experiment I, 60 mg feeding treatment significantly (p<0.05) increased the proportion of the males (85.7%) in comparison to the control group (46.67%). Lower male proportion (60%), but still significant (p<0.05), was evaluated in 30 mg feeding treatment. In experiment II, in both groups (D and E), although sex ratio was different from the theoretical 1:1 sex ratio, fish skewed toward sterility rather than masculinization because of high hormonal dozes. In conclusion, this study confirms that it is possible to achieve high rates of hormonal masculinization in Blue hap.

Keywords: Masculinization, Blue hap, 17α-methyltestosterone

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