FATTY-ACID COMPOSITION OF VENERUPIS-PULLASTRA SPAT FED ON DIFFERENT MICROALGAE DIETS

Venerupis pullastra spat were fed for 4 weeks on diets consisting of two species of algae which were supplied in single or mixed diets. The microalgal species tested were Isochrysis aff. galbana T-ISO and Tetraselmis suecica. The fatty acid pattern of the spat was basically dependent on the diet supplied. Major differences between spat cultures were detected on 14:0, 16:1n - 7, 18:0, 18:1n - 9, 18:3n - 3, 18:4n - 3, 20:5n - 3 and 22:6n - 3 fatty acids. These differences were correlated to those fatty acid contents in the diets supplied, with the exception of the 18:4n - 3 fatty acid. This acid was not detected in the Tetraselmis diet but appeared, however, in the spat fed on this microalga. This fatty acid could be obtained from linolenic acid which was present in the Tetraselmis lipids in a high proportion. Special attention was given to the essential fatty acids, 20:5n - 3 and 22:6n - 3. While I. galbana T-ISO cells contain both fatty acids, although 20:5n - 3 in a very low proportion, T. suecica is deficient in 22:6n - 3. Similarly, the T.suecica fed spat is also deficient in 22:6n - 3. Spat fed on the mixed diet shows a fatty acid profile halfway between the two algal species. The absence of 22:6n - 3 in Tetraselmis cells may explain the lower growth rate obtained with this diet.