STEROLS OF EUSTIGMATOPHYTES

The oyster cannot synthesize sterols from smaller molecules but must o btain them from its diet, which consists of detritus and small organis ms, i.e., mostly single-celled algae. Algae differ widely in their eff ectiveness as oyster food. Small (<5 mu m) algae which are abundant in sterols and polyunsaturated fatty acids appear to be most effective. Recent studies have shown the occurrence of cholesterol in strains of the unicellular algae Tetraselmis, Chaetoceros and Skeletonema, someti mes in large quantities. In the study reported here, six isolates of a recently constructed algal class, the Eustigmatophyceae, have been ex amined for sterols and fatty acids by gas chromatography and gas chrom atography/mass spectrometry. All strains were shown to contain cholest erol as the principal sterol. Two isolates contained large amounts of total sterol (400-1000 fg/cell), and one (Sticho 0-18) also contained large amounts of eicosapentaenoic acid (20:5n-3). These biochemical ch aracteristics are desirable in a potential food source for oysters.