Effect of Varying Dietary Levels of Lc-pufa and Vegetable Oil Sources on Performance and Fatty Acids of Senegalese Sole Post Larvae: Puzzling Results Suggest Complete Biosynthesis Pathway from C18 Pufa to Dha Running Title: Lc-pufa Synthesis in Senegalese Sole

(2014) Effect of varying dietary levels of LC-PUFA and vegetable oil sources on performance and fatty acids of Senegalese sole post larvae: Puzzling results suggest complete biosynthesis pathway from C18 PUFA to DHA, Comparative Biochemistry and Physiology-Part B: Biochemistry and Molecular Biology, 167, pp. 51-58. NOTICE: this is the author's version of a work that was accepted for publication in Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology. 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 Abstract 26 Lipid nutrition of marine fish larvae has focused on supplying essential fatty acids (EFA) at high 27 levels to meet requirements for growth and development. However, some deleterious effects have 28 been reported suggesting that excessive supply of EFA might result in insufficient supply of energy 29 substrates, particularly in species with lower EFA requirements such as Senegalese sole. This study 30 addressed how the balance between EFA and non-EFA (better energy sources) affects larval 31 performance, body composition and metabolism and retention of DHA, by formulating enrichment 32 emulsions containing two different vegetable oil sources (olive oil or soybean oil) and three DHA 33 levels. DHA positively affected growth and survival, independent of oil source, confirming that for 34 sole post-larvae it is advantageous to base enrichments on vegetable oils supplying higher levels of 35 energy, and supplement these with a DHA-rich oil. In addition, body DHA levels were generally 36 comparable considering the large differences in their dietary supply, demonstrating that the 37 previously reported ∆4 fatty acyl desaturase operates in vivo and that DHA was synthesized at 38 physiologically significant rates through a mechanism involving transcriptional up-regulation of 39 ∆4fad, which was significantly up-regulated in the low DHA treatments Furthermore, data 40 suggested that DHA biosynthesis may be regulated by an interaction between dietary n-3 and n-6 41 PUFA, as well as by levels of LC-PUFA, and this may, under certain nutritional conditions, lead to 42 DHA production from C18 precursors. The molecular basis of putative fatty acyl ∆5 and ∆6 43 desaturation activities remains to be fully determined as thorough searches have found only a single 44 (Δ4)Fads2-type transcript. Therefore, further studies are required but this might …