Effect of Dietary Digestible Energy Content on Expression of Genes of Lipid Metabolism and Lc-pufa Biosynthesis in Liver of Atlantic Expression of Genes of Fatty Acid Oxidation Was Less Consistent. Overall, Reduced Dietary

(2013) Effect of dietary digestible energy content on expression of genes of lipid metabolism and LC-PUFA biosynthesis in liver of Atlantic salmon (Salmo salar L.) NOTICE: this is the author's version of a work that was accepted for publication in Aquaculture. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Aquaculture, Abstract 13 The relationship between lipid and digestible energy content of the feed and growth 14 performance has been exploited with great effect in Atlantic salmon (Salmo salar). The 15 precise metabolic consequences of so-called " high-energy " feeds have not been fully defined, 16 but increased and altered tissue lipid deposition patterns impacting on carcass and product 17 quality have been reported. Recent studies on global gene expression have shown that dietary 18 lipid and digestible energy content can have significant effects on gene expression in 19 salmonids. In addition, we recently showed that functional feeds with reduced digestible 20 energy significantly improved outcomes in response to inflammatory disease in salmon. The 21 present study aimed to elucidate and clarify the effects of dietary digestible energy content 22 (22, 20 and 18 MJ/Kg; HE, ME and LE diets, respectively) on lipid and fatty acid metabolism 23 in salmon fed diets containing graded amounts of lipid. Specifically the effects on liver lipid 24 and fatty acid composition, and on the hepatic expression of genes of lipid and fatty acid 25 metabolism were determined. Final weight and weight gain were significantly higher, and 26 FCR lower, in fish fed the HE diet. Crude lipid content was significantly lower in fish fed the 27 LE diet compared to fish fed the two higher energy contents. Significantly lower total lipid 28 and triacylglycerol levels were recorded in liver of fish fed the LE diet compared to fish fed 29 the higher energy diets. Liver lipids in salmon fed the LE diet had generally significantly 30 higher proportions of saturated fatty acids and long-chain polyunsaturated fatty acids (LC-31 PUFA), and lower monounsaturated fatty acids, C18 and n-6 PUFA. Consistent with this, 32 salmon fed the LE diet showed increased liver expression of both Δ6 and Δ5 fatty acyl 33 desaturases in comparison to fish fed …