Seasonal Reproduction and Plasma Levels of Sex Steroids and Vitellogenin in Atlantic Halibut (Hippoglossus hippoglossus)

Atlantic halibut (Hippoglossus hippoglossus) collected off Newfoundland first mature at about 80 cm fork length (FL) for males and about 115–120 cm FL for females. Captive Newfoundland halibut did not release milt or eggs or have detectable levels of estradiol-17β or 11-ketotestosterone until exceeding 80 cm (males) and 115–120 cm (females). Estradiol-17β and testosterone increased to highest levels in females during gonadal recrudescence before spawning. Lower levels were observed in spawning fish. Vitellogenin (VTG) levels were highest in spawning fish. A sudden drop in estradiol-17β and VTG preceded release of the first batch of eggs. Estradiol-17β, testosterone, and VTG fluctuated with release of successive batches of eggs. Male halibut started to mature during fall and early winter, as indicated by increased testosterone and 11-ketotestosterone and abdominal swelling. Milt was first released in January and February when testosterone and 11-ketotestosterone were near maximum levels. Hence, rising levels of plasma sex steroids and VTG in fall indicate that reproductive activity is underway 1–2 mo before any noticeable swelling of the abdomen. Individual maturing halibut can be sexed by rising levels of estradiol-17β and VTG (females) and 11-ketotestosterone (males) in late fall and early winter.