Lipid content and composition of the Antarctic lamellibranch, Laternula elliptica (King & Broderip) (Anomalodesmata : Laternulidae), in King George Island during an austral summer

Total lipid content, lipid classes and fatty acid composition were studied in various tissues of the Antarctic clam Laternula elliptica in an early au stral summer. A histological examination of the gonads revealed that most o f the clams examined were spawning or ready to spawn. Lipid content was hig hest in gills (14.9% of tissue dry weight), followed by gonads (10.9%) and digestive glands (9.9%), and averaged 8.2% for the soft tissues, The overal l lipid contents were relatively low compared to temperate bivalves at a si milar reproductive stage. Lipid class composition in the total lipid of L. elliptica was quite similar to those of most marine bivalves at lower latit udes, being dominated by triacylglycerols (19.3-41.4% of total lipids) and phospholipids (18.9-28.3%) in most of the organs. Large amounts of triacylg lycerol deposits in non-reproductive tissues, particularly in siphon and gi ll, indicate a potential role of lipid as maintenance energy reserve, altho ugh the low lipid contents suggest that lipid may not serve as an energy re serve for any food-limited periods. Fatty acid composition in L. elliptica was also typical of marine bivalves with predominance of 16:0 (26%) and 20: 5n-3 (18%) acids. Total fatty acids from the soft tissues showed a moderate level of unsaturation (50.6%), and about 35% of the total fatty acids were polyunsaturated. These values were not significantly different from, or ev en lower than those of marine bivalves in warmer waters. However, the conte nt of 20:5n-3 (18.2% of total fatty acids), which dominated n-3 polyunsatur ated fatty acids, was similar to those reported for other marine bivalve sp ecies in temperate waters. The fatty acid composition of L, elliptica refle cted dietary input of some microalgal species. The nanoflagellates Cryptomo nas SPP which were reportedly rich in 16:0, 18:3n-3 and 20:5n-3, predominat ed ill the water column during the present investigation.