THE EFFECT OF MONOSPECIFIC ALGAL DIETS ON GROWTH AND FATTY-ACID COMPOSITION OF PECTEN-MAXIMUS (L) LARVAE

Four batches of Pecten maxinus (L.) larvae were grown under hatchery conditions and fed the monospecific diets Pavlova lutheri Droop, Isochrysis aff. galbana Green (clone T-iso; termed Tahitian Isochrysis), Chaetoceros calcitrans Takano and Dunaliella tertiolecta Butcher which were selected on their very different polyunsaturated fatty acid (PUFA) profiles. Neutral and polar lipid PUFA compositions of larvae were influenced by diets. The constant level of (n-3) PUFA in neutral lipids of larvae although very different in the diet indicated that neutral lipid composition was partially controlled by the larval metabolism. Similarly, the stability of total saturated, monounsaturated and PUFA levels (25, 15 and 55% of total fatty acids), as well as total (n-3) PUFA level and the preferential incorporation of the 22:6(n-3) in polar lipids clearly indicated a metabolic regulation of the fatty acid composition. The 20:4(n-6) and 22:5(n-6) acids were also preferentially incorporated. The accumulation of 18:3(n-3) or 20:5(n-3) with depletion of 22:6(n-3) in neutral and polar lipids of larvae fed diets with high levels of the first two fatty acids but little or no 22:6(n-3), indicated that elongation-desaturation of dietary fatty acids was too low in P. maximus larvae to maintain high 22:6(n-3) levels in polar lipids. The selective incorporation of dietary long chain PUFA into neutral and polar lipids by acyltransferases may be the main mechanism controlling the fatty acid composition of larvae. These results indicate that P. maximus larvae have essential requirements for long chain (n-3) and (n-6) PUFA, similar to many other marine species.