Incorporation of different fatty acids, supplied as emulsions or liposomes, in the polar and neutral lipids of Crassostrea gigas spat

Pacific oysters spat (Crassostrea gigas) were fed an algal diet (Tetraselmis suecica) whether or not supplemented with emulsions or liposomes rich in 18:1n - 9, 18:2n - 6 and 22:6n - 3. The preferential accumulation and partitioning of the latter fatty acids between the polar and neutral lipids of C. gigas spat were followed. Additionally, the efficiency of emulsions and liposomes as fatty acid carriers for C, gigas spat were compared. The incorporation of dietary fatty acids was found to vary substantially according to the fatty acid carrier (emulsions vs. liposomes), the particular fatty acid (18:1n - 9, 18:2n - 6 or 22:6n - 3), and the lipid fraction (neutral vs. polar lipids). A comparison of the percentage (% of the total fatty acids) and absolute concentration (mg g-l dry weight) of Is:ln - 9, 18:2n - 6 and 22:6n - 3 in the total lipids of C. gigas fed solely T. suecica or lipid-supplemented diets, suggest the following order of preferential accumulation: 22:6n - 3 > 18:1n - 9 > 18:2n - 6. Unlike 22:6n - 3 which was accumulated in both the neutral and polar lipid fraction of C. gigas, 18:2n - 6 and Is:ln - 9 were mainly deposited in the neutral lipids. High dietary supplies of n - 6 and/or n - 3 PUFA seriously altered the n - 3/n - 6 PUFA ratio in the neutral as well as polar lipids of spat. The fatty acid profile of emulsion-fed spat indicated a rather limited ability to elongate 18:2n - 6 to 20:2n - 6 whereas no clear evidence for desaturation to 20.4n - 6 was observed. Irrespective of the diet, nonmethylene-interrupted-dienes and plasmalogens (detected as dimethylacetals) were abundant and located nearly exclusively in the polar lipids. The ash free dry weight (AFDW) of emulsion-fed spat was significantly higher than the AFDW of liposomes-fed spat which was in turn significantly higher than the AFDW of oysters fed solely algae. The growth and fatty acid composition of liposomes-fed oysters illustrated their inferior efficiency as compared with emulsions to supplement algal diets with fatty acids. This could have been related to the small size of the liposomes vs. an emulsion. (C) 2000 Elsevier Science B.V. All rights reserved.