Hormonal sex reversal of Atlantic halibut (Hippoglossus hippoglossus L.)

Atlantic halibut (Hippoglossus hippoglossus L.) females grow larger and mature later than males, making monosex (all-female) culture economically advantageous. The objective of this research was to develop methods for the production of monosex populations of halibut through the use of sex steroids. Six hundred postlarval halibut, mean size 30.0 mm fork length (FL), were divided evenly among eight tanks and fed a formulated diet supplemented with either 17α-methyldihydrotestosterone (MDHT; 1 and 5 ppm) or 17β-estradiol (E2; 10 ppm) for 45 days. Fish were then further reared on a standard halibut diet until sex ratios could be determined through histological and macroscopic observations. The MDHT treatments yielded 97–100% males, while the E2 treatment yielded a 70–74% female population. This demonstrates that the direct feminization of halibut can be achieved, and also allows for the evaluation of indirect feminization through the crossing of hormonally masculinized females (“neomales”) to normal females.