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Arachidonic acid (ARA, 20:4n-6) fed to Seriola dorsalis juveniles at different levels was evaluated. After a seven-week feeding trial, growth performance, hepatopancreas and muscle fatty acid (FA) composition, expression of lipid-relevant genes, and blood parameters were evaluated. Four isoproteic and isolipidic experimental diets were formulated to contain 44% crude protein and 11% lipids with graded inclusion levels of ARA, 0% (Control), 0.4, 0.9, and 1.4% of the total diet. S. dorsalis juveniles (14.54 ± 0.18 g) were randomly divided into twelve tanks with fifteen animals each. The animals were hand fed three times per day to apparent satiation. Dietary treatments did not significantly affect the growth performance, SGR, FCR, and feed intake of fish. Different levels of ARA in the experimental diets directly influenced liver and muscle FA profiles, with significant changes in ARA and EPA deposition between Control treatment and 1.4%, in both tissues. The expression of arachidonate 5-lipoxygenase (alox5), acyl-CoA dehydrogenase very long chain (acadvl), carnitine O-palmitoyltransferase 1(cpt1a) was significantly affected by dietary treatments, with an expression increasing accordingly to the increasing ARA levels. In contrast, a reduction of fatty acid synthase (fas) and proliferator-activated receptor alpha (ppara) expression was significantly reduced as ARA increased in the diet. In addition, a significant reduction in blood cortisol and glucose was found at a 0.9% ARA level compared to the other treatments. Based on the performance, cortisol levels, the gene expression for eicosanoids synthesis, and lipid metabolic pathways, the present study suggests a maximum ARA inclusion of 0.9% in diets for California yellowtail juveniles, S. dorsalis. [ABSTRACT FROM AUTHOR]

This study aimed to evaluate how lipids are being catabolized or retained when offered under restriction to optimum levels by determining the genes involved in the lipid metabolism of Seriola dorsalis (yellowtail) juveniles. An eight-week nutritional trial was carried out using four isoproteic diets with various levels of lipids. Four diets were then formulated to contain 60, 90, 130, and 150 g crude fat kg−1 diet. One hundred and twenty juvenile S. dorsalis (19.15 g ± 0.67 g, mean ± SE) were located in 12 tanks of 500 L each in triplicate groups. After eight weeks of feeding experiment, while no differences were revealed in growth, significant differences were obtained in lipid deposition and lipid gene expression. While FA profile and pparα expression results corroborate that ARA, EPA, and DHA are preserved, mainly in the liver, in the muscle tissue, EPA increased significantly, while ARA and DHA remained also preserved. The results suggested that the SFAs palmitic and stearic are mainly catabolized, and then the MUFAs with oleic acid and linoleic acid. However, the lipid metabolism is reflected by the gene expression, where we found several differences. The increase in pparα shows the activation from saturated fatty acids when the palmitoleic acid is increased to be used in the β-oxidation into the mitochondria. The cptl1 , which mediates long-chain fatty acid uptake into the mitochondrion, decreases at higher crude fat (CF) levels. In comparison, the acadvl dedicated to catalyzing the LC-PUFAs into the mitochondrial β-oxidation is only expressed when the LC-PUFAs are in excess. It is concluded that apart from ratification that 13% CF is the ideal amount for S. dorsalis , it is suggested that SFAs primarily get oxidized and then the MUFAs, and linoleic acid, whereas the LC-PUFAs are only oxidized when offered in excess. • ppara expression corroborates that ARA, EPA, and DHA are efficiently preserved. • SFAs are primarily used for catabolism with palmitic and stearic acids, and then MUFA with oleic acid. • ppara activated with the presence of palmitoleic acid is increased to be used in the ß-oxidation into the mitochondria. • acadvl expression shows that LC-PUFAs are only used for catabolism, when found in excess. [ABSTRACT FROM AUTHOR]