SEASONAL REPRODUCTION AND PLASMA-LEVELS OF SEX STEROIDS AND VITELLOGENIN IN ATLANTIC HALIBUT (HIPPOGLOSSUS-HIPPOGLOSSUS)

Atlantic halibut (Hippoglossus hippoglossus) collected off Newfoundlan d 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 m ilt or eggs or have detectable levels of estradiol-17-beta or 11-ketot estosterone until exceeding 80 cm (males) and 115-120 cm (females). Es tradiol-17-beta and testosterone increased to highest levels in female s during gonadal recrudescence before spawning. Lower levels were obse rved in spawning fish. Vitellogenin (VTG) levels were highest in spawn ing fish. A sudden drop in estradiol-17-beta and VTG preceded release of the first batch of eggs. Estradiol-17-beta, testosterone, and VTG f luctuated with release of successive batches of eggs. Male halibut sta rted 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-ketot estosterone were near maximum levels. Hence, rising levels of plasma s ex steroids and VTG in fall indicate that reproductive activity is und erway 1-2 mo before any noticeable swelling of the abdomen. Individual maturing halibut can be sexed by rising levels of estradiol-17-beta a nd VTG (females) and 11-ketotestosterone (males) in late fall and earl y winter.