Monosex populations are in demand in many finfish species with sexual dimorphism, e.g., better growth performance, higher economic value. Synthetic steroids are commonly used to induce monosex population in fish but because of the potential hazards of such steroids; the use of new phytochemicals is a potential alternative to be explored. We evaluated hypothesis that red clover extract to sexually undifferentiated fry of African catfish (Clarias gariepinus) would affect their sex ratio. Five different concentrations (0, 25, 50 and 75 mg L-1) of red clover extracts and 50 µg L-1 17 β-Estradiol serving as positive control were applied by immersion method on C. gariepinus larvae for 30 days, and the effects of red clover extract on sex reversal and gonadal development were also examined at the end of 120 days.At the end of experiment, highest feminization (89%) was observed at 50 mg L-1 red clover group. Morphological and histological examinations of the gonads in all groups revealed no intersex fish. Histological examination of fish treated with red clover extract revealed no damage to the testes or ovaries. Therefore, this study suggested that red clover extract are effective in feminization of African catfish.
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