EFFECT OF ALGAL ADDITION ON STABILITY OF FATTY-ACIDS IN ENRICHED ARTEMIA-FRANCISCANA

In Artemis franciscana, enriched for 24 h with emulsified lipids, the fatty acid DKA. 22:6 omega 3) is unstable. In rotifers the level of DK A can be stabilised by adding algae rich in DHA to the fish tanks. To test this method for A. franciscana, enriched A. franciscana was incub ated with the alga Isochrysis galbana, which is rich in lipids and DHA , at six concentrations ranging from 1 to 20 mg C l(-1) at 13-14 degre es C. After Lipid enrichment, A. franciscana contained 15% lipids of w hich 79% (116 mg g DW-1) were fatty acids. Of the fatty acids, 17% was DHA (19.8 mg g DW-1). After 72 hours incubation with I. galbana, the level of DHA decreased to 1.6-3.2 mg g DW-1, which was a reduction by 84-92%. This was independent of the algal concentration. The amount of total fatty acids decreased to 53-73 mg g DW-1, a reduction by 37-54% , independent of the algal concentration. The rates of loss of the fat ty acids, and especially DHA, was greater during the first 24 h at the highest algal concentrations (8, 10 and 20 mg C l(-1)). Enriched A. f ranciscana should therefore not be incubated with high algal concentra tions (>6 mg C l(-1)) during first feeding of marine fish larvae.