FATTY-ACID COMPOSITION OF OVULATED EGGS FROM WILD AND CULTURED TURBOT(SCOPHTHALMUS-MAXIMUS) IN RELATION TO YOLK AND OIL GLOBULE LIPIDS

The fatty-acid composition of lipids from ovulated eggs of wild and cu ltured turbot was investigated in order to estimate the nutritional re quirements during embryonic and early larval development. Lipid compri sed 13.8+/-0.5% (n=5) and 13.2+/-0.7% (n=7) of the egg dry weight in w ild and cultured turbot, respectively. Polyunsaturated fatty acids (PU FA) of the (n-3) series accounted for 39% of total fatty acids in tota l lipid of both wild and cultured fish. The predominant (n-3) PUFA was docosahexaenoic acid (22:6 n-3), which also was the most abundant fat ty acid in turbot eggs and comprised 24 and 23% of the total egg fatty acids in wild and cultured fish, respectively. Phospholipids, triacyl glycerols and cholesterol-wax esters of turbot eggs all exhibited a sp ecific fatty-acid profile distinctly different from that of total lipi d. The general pattern of the fatty-acid distribution in lipids of egg s from wild and cultured turbot was similar, but the relative amount o f 18:2(n-6) was considerably higher and 20:1(n-9) slightly higher in c ultured fish. These differences were extended to all lipid classes and probably reflect the dietary intake of certain vegetable and marine f ish oils. Calculations based on light microscopical studies showed tha t 55 to 60% of the total lipids in cultured turbot eggs are confined t o the oil globule. The size of the oil globule remained constant durin g embryogenesis, and a reduction in size occurred first after hatching and mainly after yolk depletion. This implies that the total amount o f lipids utilised during the embryonic development is considerably les s than the total lipids present in ovulated turbot eggs. Comparison of the fatty-acid composition of total lipids from eggs and vitellogenin of wild turbot reveals that egg lipids contained a lower level of sat urated and a higher level of monounsaturated fatty acids. Eggs also co ntained wax esters, which were not detected in vitellogenin, suggestin g that vitellogenin is not the only source of lipids for turbot eggs.