Gonadal sex differentiation and hormonal sex reversal of Atlantic halibut (Hippoglossus hippoglossus, L.)

Female Atlantic halibut (Hippoglossus hippoglossus L.) grow larger and mature later than males, allowing monosex (all-female) culture to become economically advantageous. The purpose of this study was to identify the stages of gonadal sex differentiation in Atlantic halibut, and use this information for methods of sex reversal. In this study, halibut gonadal sex differentiation was described histologically using 338 larvae (10 mm standard length to 230 mm fork length). The results show that differentiation occurred by 38.0 mm FL, which coincides with the weaned, post-metamorphic, settled stage. In aquaculture for human consumption, both direct (estrogen-mediated) and indirect (androgen-mediated) feminization must be considered. Six hundred halibut (mean = 30.0 mm FL), were fed artificial pellets supplemented with 17alpha-methyldihydrotestosterone (1 and 5 ppm) or 17beta-estradiol (10 ppm) for 45 days. Masculinization was 97--100% successful in both androgen treatments, while the single estrogen treatment resulted in only 70--75% feminization. The results of these experiments are directly relevant to halibut aquaculture in Canada.