FATTY-ACID COMPOSITION OF RUDITAPES DECUSSATUS SPAT FED ON DIFFERENT MICROALGAE DIETS

The fatty acid composition of the Ruditapes decussatus spat fed on thr ee different microalgal diets during 4 weeks was determined. The fatty acid pattern of each diet was also analysed. The diets used were Isoc hrysis galbana, clone T-ISO, Tetraselmis suecica, and Phaeodactylum tr icornutum. The fatty acid composition of the spat was usually well cor related with that of the diet supplied. Major differences among spat c ultures were found in 14:0, 16:0, 16:1n-9, 16:1n-7, 18:1n-9, 18:2n-6, 18:3n-3, 18:4n-3, 20:5n-3, 22:5n-6 and 22:6n-3 fatty acids. These diff erences were correlated with the particular fatty acid content of each diet supplied. It has been shown that R. decussatus spat have a very low capacity to elongate and desaturate linolenic acid to n-3 PUFA, so when 20:5n-3 or 22:6n-3 were not present in the diet, they were also absent, at least in measurable amounts, in the clams. The absence of a ny of the ''essential'' fatty acids, 20:5n-3 in T-ISO or 22:6n-3 in Te traselmis, did not limit spat growth, so their role as ''essential'' f atty acids might be a matter for discussion. Finally, the nutritive va lue of each diet was discussed in terms of its fatty acid composition.