LIPID CLASSES AND THEIR CONTENT OF N-3 HIGHLY UNSATURATED FATTY-ACIDS(HUFA) IN ARTEMIA-FRANCISCANA AFTER HATCHING, HUFA-ENRICHMENT AND SUBSEQUENT STARVATION

The distribution of n-3 highly unsaturated fatty acids (HUFA) over the major neutral and polar lipid classes was determined for two predomin ant types of live food used in the larviculture of marine fish and shr imp, i.e. freshly hatched and HUFA-enriched Artemia, and compared with data reported in the literature for wild copepods, representing the n atural diet of these larvae. Lipid class composition and their content of n-3 HUFA, particularly eicosapentaenoic acid (EPA, 20:5n-3) and do cosahexaenoic acid (DHA, 22:6n-3), were assessed in freshly hatched, H UFA-enriched and subsequently starved Artemia franciscana. The n-3 HUF A enrichment was based on feeding Artemia a lipid emulsion in which ei ther fatty acid ethyl esters (EE, diluted with olive oil) or triacylgl ycerol (TAG) provided a level of 30% n-3 HUFA. Enrichment of Artemia w ith either type of the lipid emulsions resulted in an increase of tota l lipid content from 20.0 to 28.2-28.7% of dry matter mainly due to th e accumulation of neutral lipid, primarily TAG (from 82 to 158 mg g(-1 ) dry wt in freshly hatched and 24-h enriched Artemia). Enriched brine shrimp utilized up to 27-30% of their TAG content during 72 h of star vation at 12 degrees C. The absolute tissue concentrations of polar li pids remained constant at 71 to 79 mg g(-1) dry wt throughout the enri chment and subsequent starvation. The level of n-3 HUFA increased dras tically during enrichment from 6.3% of total fatty acids (8.2 mg g(-1) dry wt) in freshly hatched nauplii to between 20.4 and 21.8% (40.4 to 43.2 mg g(-1) dry wt) in 24-h enriched Artemia and was not significan tly affected by the source of n-3 HUFA. During starvation, 18:0, 20:4n -6 and 20:5n-3 were retained, whereas 18:4n-3, 22:5n-3 and 22:6n-3 wer e specifically catabolized. The major polar lipids, phosphatidylethano lamine (PE) and phosphatidylcholine (PC), of freshly hatched Artemia s howed very low levels of DHA (< 0.1% of total fatty acids) and carried about 45% of the total EPA present. Enrichment with either of the emu lsions resulted in an increase of the neutral lipid fraction which con centrated > 64% of the EPA and > 91% of the total DHA present. This is in sharp contrast with the high levels of n-3 HUFA, in particular DHA , in the polar lipid fraction reported for wild copepods. The contrast ing distribution of DHA in the neutral and polar lipid fractions of en riched brine shrimp compared to the natural diet may influence the eff icacy of this essential fatty acid for marine fish larvae in aquacultu re systems.