FIRST FEEDING OF ATLANTIC HALIBUT (HIPPOGLOSSUS-HIPPOGLOSSUS) USING DIFFERENT COMBINATIONS OF ARTEMIA AND WILD ZOOPLANKTON

Larvae of Atlantic halibut were offered different combinations of Arte mia and wild zooplankton during first feeding to examine the effects o n feeding incidence, growth, survival and pigmentation. Free amino aci d and fatty acid composition in feeds and fish larvae were also analys ed. The free amino acid concentration in unenriched Artemia averaged 4 5 mu mol/g w.w., compared to 116 mu mol/g w.w. in the wild zooplankton . Super Selco(TM) (Artemia Systems, Belgium)-enriched Artemia increase d the concentration to 57 mu mol/g w.w. on average, and also increased the lipid content in Artemia to approximately the levels found in wil d zooplankton (3.0% of wet weight), though with a much lower n-3 PUFA content. Larvae fed 19 days on enriched Artemia (EA) were significantl y larger than larvae fed wild zooplankton (Z), wild zooplankton for 7 days then unenriched Artemia (Z7) or unenriched Artemia (UA). The EA g roup also showed the best survival at day 19, 28.7% (19.9-34.4%) compa red to 14.0% (13.2-14.7%) in the Z group and 13.6% (10.5-18.3%) in the Z7 group. Also the UA group had significantly higher survival 22.8% ( 18.8-25.5%) than the Z group, but showed slower growth. The fatty acid composition of larvae fed Artemia showed a development towards the co mposition of their feeds, while the fatty acid composition in the larv ae fed wild zooplankton remained relatively similar to that of prefed larvae. After 57 days of feeding, high frequencies of malpigmented juv eniles were observed in the UA and EA groups (95.7 and 70.6%, respecti vely) as well as in the 27 group (80.8%). All larvae fed wild zooplank ton or larvae transferred from an unenriched Artemia diet to a diet of wild zooplankton from day 19 onwards, became normally pigmented. The present experiment showed that use of Artemia could be successful in p roviding growth and survival in the early larval stage of exogenous fe eding in Atlantic halibut, but had negative effects on pigmentation la ter on. However, by introduction of wild zooplankton prior to a critic al stage (found to be beyond 19 days of feeding) these effects could b e eliminated.