Spawning individuals of the scallop Pecten maximus were conditioned on three test diets: Tahiti Isochrysis, a mixture (PTSC) and Chaetoceros calcitrans. The scallops fed T-Isochrysis showed a better hatching rate and lower atresia than those fed the other two diets. Proximate composition of the female gonads was not modified by the differences in the diets. Enrichment of gonads with sterol esters and triglycerides, characteristic of storage of lipids, observed with the broodstock fed the diatoms, did not result in successful gametogenesis and spawning. The monounsaturated fatty acid (MUFA) and polyunsaturated fatty acid (PUFA) composition of neutral and polar lipids of gonads was related to the fatty acid composition of the diet. However, the 20 and 22 carbon PUFA were maintained at levels relatively independent of those of the diet; when these fatty acids were low in the diet, their concentration in the lipids of the gonads decreased but still remained significant. This effect was more pronounced in the polar than the neutral lipids. The preferential incorporation of 22:6n-3, 20:4n-6 and 20:5n- 3 in the polar lipids indicates their role in gametogenesis and embryogenesis. The sterol composition of the gonads (free sterols and sterol esters) reflected that of the diet; however, the cholesterol, mainly found in the esterified fraction, was maintained at stable levels independent of dietary supply. Two sterols (22-dehydrocholesterol and 24- methylenecholesterol) that were either absent from, or present only in trace amounts in the diets, were found to occur at constant levels in the female gonads, regardless of the nature of the diet.
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