CHANGES IN THE FATTY-ACID COMPOSITION OF PECTEN-MAXIMUS (L) DURING LARVAL DEVELOPMENT

The fatty acid composition of Pecten maximus (L.) larvae grown under hatchery conditions was determined during development from the oocyte stage to the pediveliger stage (Day 23). The levels of total fatty acids in neutral and polar lipids increased 3 days after the first feeding and were almost-equal-to 10 times higher in pediveligers than in D-larvae (32.46 vs. 3.14 ng-larva-1 and 11.38 vs. 1.23 ng-larva-1 in neutral and polar lipids, respectively). The proportions of total saturated, monounsaturated and polyunsaturated fatty acids in neutral and polar lipids remained stable throughout the development. The fatty acid composition of P. maximus larvae was typical of that described for other marine bivalve larvae since the (n-3) polyunsaturated fatty acids (PUFA) formed 34.4-39.6 % of the neutral lipids and 43.0-50.7 % of the polar lipids. The major PUFA identified in oocytes and larvae were similar to those supplied by the diet [ 18:2(n-6), 18:4(n-3), 20:5(n-3) and 22:6(n-3)]. We observed that significant changes of the PUFA composition occurred in neutral and polar lipids during embryogenesis and the subsequent nutritional transition. These changes were expressed by the relative decline of the 20:5(n-3) and 20:4(n-6) percentage levels in both lipid fractions while the 22:6(n-3) increased in neutral lipids and the 22:5(n-6) increased in both neutral and polar lipids. We observed also that polar lipids exhibited a 22:6(n-3) level considerably higher than that of the diet (26.8 vs. 6.8 %) and constant throughout development, indicating a preferential incorporation and a major structural role. These results suggest that a metabolic control of the fatty acid composition of neutral lipids and mainly polar lipids takes place in developing larvae. With reference to previous studies on fatty acid metabolism of molluscs, it is probable that this control results from a selective incorporation of dietary fatty acids by acyltransferases rather than a desaturation of dietary precursors. P. maximus larvae seem therefore to have a high nutritional requirement for long chain PUFA and especially the 22:6(n-3).