Fatty Acid Composition of Three Cultured Algal Species (Isochvysis galbana, Chaetoceros gracilis and Chaetoceros calcitrans) Used as Food for Bivalve Larvae

Fatty acids of three cultured unicellular algae wldely used in aquaculture ( Isochrysis galbana , clone T‐iso, Chaetoceros calcitrans , and Chaetoceros gracilis ) were analyzed in detail by gas‐liquid chromatography and mass spectrometry. Fatty acid compositions of the individual species, harvested at monthly intervals during a four month period, showed a very consistent pattern. Shorter chain (C16) fatty acids accounted for more than 70% of total fatty acids in the diatoms but less than 20% in I. galbana . Medium chain (C18) and the long chain 22:6w3 unsaturated fatty acids represented more than 50% of the total fatty acids in I. galbana but less than 10% of the total In the Chaetoceros spp. However, in the latter, 20:5w3 replaced 22:6w3 at an equivalent level. Fatty acid profiles of c. calcitrans and c. gracilis were similar, except that the latter contained lower levels of 16:2w4, 16:3w4 and 16:4w1, and higher levels of 18:2w6 and 18:3w6. In particular C. gracilis contained a higher proportion of the biochemically important fatty acid 20:4w6 (arachldonic acid). One of the salient features of I. galbana lipids was the presence of the fatty acid 18:5w3. This fatty acid is not generally reported in algae or invertebrate lipid analyses, but is a typical component of I. galbana and of other marine photosynthetic flagellates. Its potential for utilization by aquatic organisms is unknown.