The use of low fishmeal/fish oil in marine fish diets affects dietary essential fatty acids (EFAs) composition and concentration and, subsequently, may produce a marginal deficiency of those fatty acids with a direct impact on the fish intestinal physiology. Supplementation of essential fatty acids is necessary to cover the requirements of the different EFAs, including the ones belonging to the n-6 series, such as arachidonic acid (ARA). ARA, besides its structural role in the configuration of the lipid classes of the intestine, plays an important role in the functionality of the gut-associated immune tissue (GALT). The present study aimed to test five levels of dietary ARA (ARA0.5 (0.5%), ARA1 (1%), ARA2 (2%), ARA4 (4%), and ARA6 (6%)) for European sea bass (Dicentrarchus labrax) juveniles in order to determine (a) its effect in selected distal intestine (DI) lipid classes composition and (b) how these changes affected gut bacterial translocation rates and selected GALT-related gene expression pre and post challenge. No differences were found between distal intestines of fish fed with the graded ARA levels in total neutral lipids and total polar lipids. However, DI of fish fed with the ARA6 diet presented a higher (P < 0.05) level of phosphatidylethanolamine (PE) and sphingomyelin (SM) than those DI of fish fed with the ARA0.5 diet. In general terms, fatty acid profiles of DI lipid classes mirrored those of the diet dietary. Nevertheless, selective retention of ARA could be observed in glycerophospholipids when dietary levels are low (diet ARA0.5), as reflected in the higher glycerophospholipids-ARA/dietary-ARA ratio for those animals. Increased ARA dietary supplementation was inversely correlated with eicosapentaenoic acid (EPA) content in lipid classes, when data from fish fed with the diets with the same basal composition (diets ARA1 to ARA6). ARA supplementation did not affect intestinal morphometry, goblet cell number, or fish survival, in terms of gut bacterial translocation, along the challenge test. However, after the experimental infection with Vibrio anguillarum, the relative expression of cox-2 and il-1β were upregulated (P < 0.05) in DI of fish fed with the diets ARA0.5 and ARA2 compared with fish fed with the rest of the experimental diets. Although dietary ARA did not affect fish survival, it altered the fatty acid composition of glycerophospholipids and the expression of pro-inflammatory genes after infection when included at the lowest concentration, which could be compromising the physical and the immune functionality of the DI, denoting the importance of ARA supplementation when low FO diets are used for marine fish.

在海水鱼的饮食中使用低鱼粉/鱼油会影响饮食中必需脂肪酸（EFA）的成分和浓度，随后可能会导致这些脂肪酸的边缘缺乏，直接影响鱼的肠道生理。必须补充必需脂肪酸才能满足不同EFA的要求，包括属于n-6系列的EFA，例如花生四烯酸（ARA）。ARA除了在肠道脂质类别的结构中发挥结构性作用外，还在肠道相关免疫组织（GALT）的功能中发挥重要作用。本研究旨在测试欧洲鲈鱼的膳食ARA的五个含量水平（ARA0.5（0.5％），ARA1（1％），ARA2（2％），ARA4（4％）和ARA6（6％））（香茅）以确定（a）在选定的远端肠（DI）脂质类别组成中的作用以及（b）这些变化如何影响肠道细菌易位率以及攻击前后的GALT相关基因表达。以总中性脂质和总极性脂质中分级ARA水平饲喂的鱼的远端肠之间没有发现差异。但是，以ARA6饮食喂养的鱼的DI含量较高（P 饲喂ARA0.5日粮的鱼的磷脂酰乙醇胺（PE）和鞘磷脂（SM）含量<0.05）。一般而言，DI脂质类别的脂肪酸谱与饮食中的那些相似。然而，当饮食水平低时（饮食ARA0.5），可以在甘油磷脂中观察到ARA的选择性保留，这反映在那些动物的较高的甘油磷脂/ ARA /饮食-ARA比值上。当从鱼类中饲喂基础成分相同的饮食数据（饮食ARA1至ARA6）时，ARA饮食补充的增加与脂质类中二十碳五烯酸（EPA）含量成反比。挑战试验中，就肠道细菌易位而言，补充ARA不会影响肠道形态，杯状细胞数或鱼类存活率。但是，经过实验感染后 与饲喂其余实验饲料的鱼相比，饲喂ARA0.5和ARA2的鱼的DI中的鳗弧菌，cox-2和il-1β的相对表达上调（P <0.05）。尽管饮食中的ARA不会影响鱼类的生存，但当以最低的浓度摄入时，它会改变感染后甘油磷脂的脂肪酸组成和促炎基因的表达，这可能会损害DI的物理和免疫功能，表明当低FO饮食用于海鱼时，ARA补充的重要性。