Status of the cultivation technology for production of Atlantic halibut ( Hippoglossus hippoglossus) juveniles in Norway/Europe

Abstract

Comprehensive research programs form the basis for the commercial juvenile production technology of Atlantic halibut ( Hippoglossus hippoglossus) in Europe, and commercial production is currently being tested in Iceland, Scotland, and Norway. Broodstocks of halibut are normally maintained in cylindrical tanks (diameter 5–15 m, 1-m depth, light-protected, 34‰ salinity, temperature <8°C). Each female releases several batches of eggs (4–16 per season, 3–4-day intervals), and manipulation of the photoperiod may be used to have continuous egg production. Eggs are obtained by stripping; at least 90% of the eggs are normally fertilised, and 75–80% of the fertilised eggs hatch. The eggs must be disinfected before hatching, and appropriate treatment by glutaric aldehyde is most efficient. The disinfected eggs are normally hatched in large flow through systems in which the larvae are maintained during their prolonged critical yolk sac stage. The fragile yolk sac larvae are very sensitive to physical and microbial conditions, and must be handled with care. Survival during the yolk sac stage may be as high as 50–70% of the initial population, however, jaw deformation is a main problem. Density during first feeding is normally 0.5–5 larvae l −1. The feeding regime used in commercial production in Norway consists of harvested marine copepods and Artemia nauplii. International feeding technology with cultivated live feed is being adapted to commercial scale. The dietary components used are microalgae, rotifers, short-term enriched Artemia nauplii, and larger Artemia juveniles. The larval feeding period lasts for ca. 60 days. Light conditions are critical for survival in the initial stage of feeding, and a component of UV-light and appropriate shading is needed for adequate larval behaviour. Nutritional and microbial conditions are more important for older stages. The results with rotifers and Artemia have gradually improved over the last few years. Halibut larvae have high requirements for DHA (docosahexaenoic acid, 22:6 n−3), and the supply of DHA through Artemia has turned out to be a major problem, probably because of the high DHA-catabolism of Artemia. Poor pigmentation of the fry and the low larval resistance to stress are frequently observed. The numbers of weaned halibut fry transferred to the growout phase in Europe have been quite variable; approximately 370,000 in 1997. The price for halibut fry is on the order of US$12 per fry.