REASSESSMENT OF LIPID-COMPOSITION OF THE DIATOM, SKELETONEMA-COSTATUM

In the present work, we questioned the natural or artifactual origin of the large amounts of free fatty acids recovered in lipids from the diatom Skeletonema costatum. Using rapid cell harvest and a very drastic method to extract the lipids, we demonstrated that these lipid patterns rich in free fatty acids were relevant to the degradation of complex lipids. A revised lipid composition of S. costatum is given which differs from those previously described by the absence of free fatty acids, while the proportion of polar lipids is substantially increased. Membrane lipids are mostly represented and storage lipids are less abundant, since we analysed the cells during their exponential growth phase. However, the fatty acid composition is in agreement with previous data. Polyunsaturated fatty acids (PUFA) consist essentially of 20:5 omega 3, 16:3 omega 4 and 16:4 omega 1, while 16:1 omega 7 is the main monounsaturated FA. This confirms that, with regard to its lipid composition, the diatom, S. costatum, provides a good diet for molluscs, particularly through its high proportion of omega 3 PUFA. Using this extraction procedure, sterols were found to be identical to previous results but a new compound, a 18:1 fatty alcohol, was detected. The consequences of this reassessement on the lipid compositions of diatoms so far published and their application to the lipid diet of mollusc larvae in aquaculture are discussed.