REARING HALIBUT IN NORWAY - PRESENT PRACTICES AND CHALLENGES

Atlantic halibut (Hippoglossus hippoglossus L.) has been identified as the species that can best complement the salmon farming industry in N orway. From an experimental fry production of only 2 in 1985 to a prod uction of Over 350000 in 1994 and commercial sales of 69 t in 1995, th e advances have accumulated through close cooperation between research and industry. Current practices involve holding the broodstock on nat ural or controlled photoperiod, stripping and disinfecting eggs before incubation in darkness, controlling larval placement in the water col umn, and first-feeding on natural zooplankton in green water. Many of the original practices are being examined with a critical eye, such as use of salt during removal of bottom water and the necessity of maint aining the larvae in darkness beyond 150 degree-days. Early temperatur e regimes play a role in viability, and experimental evidence points t o changing temperature optima with size and to effects of light and ph otoperiod on growth, behaviour and survival in most stages. Challenges include identification of the period in which pigmentation is affecte d by exogenous nutrients, control and synchronization of metamorphosis , early identification and separation of the fast-growing females in t he populations, and prevention of the early maturation in males. These and other biological and environmental requirements of the developing halibut must be better understood to achieve predictable production r outines.