Effects of Dietary Fatty Acid Ethyl Esters on Polar and Nonpolar Tissue Lipids in Red Drum, Sciaenops Ocellatus.

Abstract

Red drum juveniles of mean initial weight 9.23 $\pm$ 0.27 g were kept in indoor aquaria. The water was maintained at a salinity of 12 $\pm$ 0.5 ppt. The fish were fed six isonitrogenous (38% crude protein) and isocaloric (1.36 $\times$ 10$\sp4$ kJ/kg), purified diets differing in lipid content, for nine weeks, to investigate the effects of selected dietary essential fatty acids (EFA) on growth performance and tissue fatty acid composition. Each diet, except the low-fat (LF) diet, contained 8% total lipid from (1) menhaden fish oil (MFO), (2) oleate (18:1n-9) supplemented with linoleate (18:2n-6), (3) linolenate (18:3n-3), (4) a mixture of linoleate and linolenate, or (5) docosahexaenoate (22:6n-3). All fatty acids were provided as ethyl esters (FAEE). Fish fed MFO had highest weight gain and feed efficiency. Weight gain and feed efficiency of fish fed the LF diet was intermediate to that of fish fed MFO and FAEEs. Fish fed FAEE diets had the lowest weight gain and feed efficiency. There was no significant difference in weight gain and feed efficiency among fish fed the FAEE diets. Tissue fatty acid composition generally reflected the fatty acid composition of dietary lipid. Levels of saturated fatty acids (SFAs) in tissues were independent of levels of SFA in the diet. However, fish fed LF and FAEE diets had a decreased level of total SFAs in tissue, while fish fed MFO did not. Levels of monoenoic fatty acids were significantly lower in fish fed MFO than in those fed LF and FAEE diets. N-6 PUFAs were depleted in fish fed diets that did not contain 18:2n-6. N-3 PUFAs increased in muscle lipid of fish fed diets containing 18:3n-3. N-3 highly unsaturated fatty acids (HUFAs) were conserved in the polar lipid fraction of tissues. Results suggest that the poor growth of fish fed FAEE diets was probably due to the poor palatability and unusual fatty acid composition of those diets. The red drum has very limited ability to chain-elongate and desaturate fatty acids, and presumably has EFA requirements for long-chain unsaturated fatty acids, such as eicosapentaenoic acid (EPA, 20:5n-3), docosahexaenoic acid (DHA, 22:6n-3) and arachidonic acid (20:4n-6), as do other marine species studied to date.