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 Norway. From an experimental fry production of only 2 in 1985 to a production of over 350000 in 1994 and commercial sales of 60 t in 1995, the advances have accumulated through close cooperation between research and industry. Current practices involve holding the broodstock on natural or controlled photoperiod, stripping and disinfecting eggs before incubation in darkness, controlling larval placement in the water column, 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 maintaining the larvae in darkness beyond 150 degree-days. Early temperature regimes play a role in viability, and experimental evidence points to changing temperature optima with size and to effects of light and photoperiod on growth, behaviour and survival in most stages. Challenges include identification of the period in which pigmentation is affected by exogenous nutrients, control and synchronization of metamorphosis, early identification and separation of the fast-growing females in the 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 routines.