EFFECT OF MICROALGAL DIETS AND COMMERCIAL WHEAT-GERM FLOURS ON THE LIPID PROFILE OF RUDITAPES DECUSSATUS SPAT

The influence of both the lipid composition of microalgal diets and co mmercial flours on the lipid classes and fatty acids of Ruditapes decu ssatus spat was studied. These aspects of the nutritional value of the diets were discussed in relation to the growth of the spat. Four diet s were tested; Diet A, composed of 100% of the daily food ration of mi croalgae; Diet B, composed of 100% of wheatgerm; Diet C, composed of 5 0% of microalgae and 50% of wheatgerm; and Diet D, composed of 25% of microalgae and 75% of wheatgerm. The microalgal cells present a higher lipid content than that for wheatgerm. Tahitian Isochrysis cells have phospholipids and triacylglycerols as majority lipids, whereas in the wheatgerm particles, the lipids more abundant are triacylglycerols. F atty acid content was higher in the microalgal cells than in the wheat germ particles. The n-3 fatty acids were the most abundant acids in th e microalgae, whereas the n-6 fatty acids were in the wheatgerm. The n -3 PUFA were not detected in wheatgerm. Phospholipids were the main li pids present in the clam spat, followed by triacylglycerols. Other lip id classes, detected in significantly lower amounts, included free fat ty acids, sterols, and sterol ester + waxes. The composition of fatty acids in the spat was influenced by the fatty acid composition of the diet. Highest spat growth rates were observed with those diets that pr esent a higher phospholipid/triacylglycerol relation. A negative corre lation in the relation n-6/n-3 vs. growth has also been observed, with better growth rates in diets with a lower ratio. Ii the fatty acid 20 :5n-3 and 22:6n-3 considered ''essential'' for marine animals were not present in the diet, they were not present in the spat either. Desatu ration and elongation capabilities of R. decussatus spat were also dis cussed. (C) 1998 Elsevier Science Inc.