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The fatty-acid composition of lipids from ovulated eggs of wild and cultured turbot was investigated in order to estimate the nutritional requirements during embryonic and early larval development. Lipid comprised 13.8±0.5% (n=5) and 13.2±0.7% (n=7) of the egg dry weight in wild and cultured turbot, respectively. Polyunsaturated fatty acids (PUFA) of the (n-3) series accounted for 39% of total fatty acids in total lipid of both wild and cultured fish. The predominant (n-3) FUFA was docosahexaenoic acid (22:6 n-3), which also was the most abundant fatty acid in turbot eggs and comprised 24 and 23% of the total egg fatty acids in wild and cultured fish, respectively. Phospholipids, triacylglycerols and cholesterol-wax esters of turbot eggs all exhibited a specific fatty-acid profile distinctly different from that of total lipid. The general pattern of the fatty-acid distribution in lipids of eggs from wild and cultured turbot was similar, but the relative amount of 18:2(n-6) was considerably higher and 20:1(n-9) slightly higher in cultured fish. These differences were extended to all lipid classes and probably reflect the dietary intake of certain vegetable and marine fish oils. Calculations based on light microscopical studies showed that 55 to 60% of the total lipids in cultured turbot eggs are confined to the oil globule. The size of the oil globule remained constant during embryogenesis, and a reduction in size occurred first after hatching and mainly after yolk depletion. This implies that the total amount of lipids utilised during the embryonic development is considerably less 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 saturated and a higher level of monounsaturated fatty acids. Eggs also contained wax esters, which were not detected in vitellogenin, suggesting that vitellogenin is not the only source of lipids for turbot eggs.

Recently, we found that liver of squirrelfish (Holocentrus rufus) from Bermuda contains remarkably high concentrations of metallothionein (MT) and Zn. To clarify the nature and cause of the Zn accumulation, four Holocentridae species from three genera (Neoniphon sammara, Sargocentron spiniferum, Myripristis violacea, and Myripristis murdjan) were collected from a totally different area, the Great Barrier Reef, Australia. The average hepatic Zn levels in these species ranged from 67 μg g-1 (S. spiniferum) to 1000 μg g-1 (N. sammara). The intraspecies variation in the hepatic Zn level was pronounced. In both N. sammara and M. murdjan, there was a 48-fold difference between the lowest and the highest Zn concentration. Zn accumulation was closely correlated to a dramatically elevated concentration of MT in liver. In N. sammara, which possessed the highest level of MT among the investigated species, the mean hepatic MT concentration was 19 500 μg g-1. Subcellular fractionation of the liver showed that MT was responsible for the binding of up to 74% of the hepatic Zn. The concentrations of MT and Zn in gills were low, suggesting that Zn storage in fish within this family is tissue-specific. The results further indicate that the high concentrations of MT and Zn in Holocentridae liver are linked to normal physiological processes. We suggest that the Holocentridae family may be a unique model for future studies of Zn metabolism and the function of MT.