Fatty Acid Compositions of Various Tissue Lipids in the Marine Bivalves, Megangulus venulosus and Megangulus zyonoensis, from Coastal Waters of Hokkaido, Northern Japan

Various tissue lipids from the marine bivalves, Megangulus venulosus (M. venulosus) and Megangulus zyonoensis (M. zyonoensis), were analyzed for comparison of major fatty acids and their distribution. The main fatty acid components in this genus in all tissues were found to be 16:0 (11.0-15.2%), 18:0 (4.1-8.6%), 20:5n-3 (13.3-25.6%) and 22:6n-3 (8.1-16.7%), with n-3 polyunsaturated fatty acids most abundant. The proportion of 20:5n-3 was higher in M. zyonoensis than in M. venulosus, and 22:6n-3 was higher in M. venulosus than in M. zyonoensis. The proportions of 20:5n-3 and 22:6n-3 were highest in muscle tissue lipids from M. venulosus and M. zyonoensis, at 33.1% and 36.2%, respectively. The distribution of major fatty acid components in neutral (NL) and polar lipids (PL) was determined, with 16:0 and 20:5n-3 shown for NL, and 16:0, 20:5n-3 and 22:6n-3 for PL. The proportion of 22:6n-3 in NL and PL differed significantly, 22:6n-3 being much higher in PL. The main branched fatty acid component, 4,8,12-trimethyltridecanoic acid, was found mainly in PL of viscera tissues from either species. In addition, 2-hydroxypentadecanoic, 2-hydroxyhexadecanoic and 2-hydroxyheptadecanoic acids were also found to be present in the two species and this presence of 2-hydroxy fatty acids in the genus Megangulus is reported here for the first time.