LAUSR

Abstract Vegetable oils (VO) are being extensively used as lipid sources in marine fish diets, due to the decreased availability of fish oil. The use of VO could induce some imbalances on essential fatty acids (EFAs) with the subsequent well described detrimental effects on fish immunity. EFAs are directly associated with several immune functions, acting as important elements for the fluidity of cytoplasmic membranes and as precursors of eicosanoids. At intestinal level, eicosanoids produced via cyclooxygenase (COX-2) enzymes are involved in gastrointestinal cyto-protection by influencing the homeostasis regulation and the onset of gut inflammation process through the action on eicosanoid receptors (EPs), which modulate gastrointestinal mucosal integrity amongst other functions. Senegalese sole is a flatfish with high susceptibility to deleterious effects due to stress and diseases and highly sensitive to changes in dietary fatty acids. In this study, Senegalese sole juveniles were fed diets (56% crude protein, 12% crude lipid) containing linseed (100LO), soybean (100SO) or fish (100FO) oils as unique oil source. Intestinal fatty acid composition plus relative expression of intestinal EPs and other genes related with eicosanoid cascade were determined after 90 days. Moreover, at the end of the experiment a stress test (5 min of net chasing) was carried out. The use of VO altered the fatty acid profile of intestine and the expression of EP genes. The use of SO (rich in n-6 fatty acids) induced an overexpression of cox-2 in basal (non-stress) situation, plus a down-regulation of intestinal ep4 gene expression. Besides, fish fed soybean oil in the diet seems to be unable to respond properly to chasing stress.