LARVAL-REARING TECHNOLOGY OF MARINE SPECIES IN NORWAY

The Cultivation techniques of the marine cold water species turbot (Sc ophthalmus maximus), Atlantic halibut (Hippoglossus hippoglossus) and Atlantic cod (Gadus morhua) have been developed in Norway during the l ast decade. Research programs have been undertaken to establish the sc ientific basis for a commercial, feasible juvenile production technolo gy. The Atlantic halibut must be carefully maintained in flow through silo systems during their prolonged critical yolk sac stage (30 days). The period of first feeding lasts for approximately 80 days, and cope pods and Artemia are in most cases used as live feed. The halibut larv ae have high requirements for n-3 HUFA, in particular DKA. More effici ent enrichment techniques for Artemia and more reliable first feeding technology are still major challenges for this species. Commercial pro duction of halibut is still in its early phase, but the numbers produc ed have increased steadily during the last few years, with the excepti on for 1995. The number of weaned halibut fry transferred to the growo ut phase was approximately 370 000 in 1994 and less than 100 000 in 19 95. The production costs range between 5-6 US$ per fry. The rearing te chnology for juvenile turbot is well established. Turbot larvae are cu ltured using classical intensive rearing techniques with microalgae, r otifers and Artemia as live feed. The larval densities are kept rather low by commercial producers (<5 1(-1)), but densities in research pro jects are normally much higher (<100 larvae per litre). The survival t hrough the larval stage is normally both predictable and relatively hi gh (10-50%). Improvements in fry quality, e.g. growth potential and vi ability, are higher priorities than improvement in survival. The numbe r of fry produced in Europe in 1995 was some 2.5 million, and depended on fry requirements rather than technical constraints. Production cos ts range between 1.3-1.4 US$ per fry. The rearing technology of Atlant ic cod is similar to that of turbot, but the dietary requirements of c od, as well as most research objectives, are comparable to those of ha libut. God, however, currently has a limited commercial potential. The number of cod juveniles produced in 1995 was approximately 300 000, a ll produced in poll systems as part of restocking projects. Establishe d hatchery techniques may be utilized for commercial production of cod juveniles if the production costs of cultivated cod is lower than the price obtained for wild caught cod.