Modulation of the expression of components of the metabolic stress response by dietary 1 arachidonic acid in European sea bass ( Dicentrarchus labrax ) larvae 2

52 This study reports for the first time in European sea bass, Dicentrarchus labrax (L.), larvae, 53 the effect of different levels of dietary arachidonic acid (ARA; 20:4n-6) on the expression of 54 genes related to the fish stress response. Copies of mRNA from genes related to 55 steroidogenesis (StAR (steroidogenic acute regulatory protein), c-Fos, and CYP11β (11β56 hydroxylase gene)), glucocorticoid receptor complex (GR (glucorticoid receptor) and HSP 57 (heat shock proteins) 70 and 90) and antioxidative stress (catalase (CAT), superoxide 58 dismutase (SOD), and glutathione peroxidase (GPX)) were quantified. Eighteen day-old 59 larvae were fed for 14 days with three experimental diets with increasing levels of ARA 60 (0.3, 0.6 and 1.2% d.w.) and similar levels of docosahexaenoic (DHA; 22:6n-3) and 61 eicosapentaenoic (EPA; 20:5n-3) acids (5 and 3%, respectively). The quantification of 62 stress-related genes transcripts was conducted by One-Step TaqMan real time RT-PCR 63 with the standard curve method (absolute quantification). Increase dietary levels of ARA 64 induced a significantly (p<0.05) down-regulation of genes related to cortisol synthesis, 65 such as StAR and CYP11β and up-regulated genes related to glucocorticoid receptor 66 complex, such as HSP70 and GR. No effects were observed on antioxidant enzymes gene 67 expression. These results revealed the regulatory role of dietary ARA on the expression of 68 stress-related genes in European sea bass larvae. 69