N-3 essential fatty acids in Nile tilapia, Oreochromis niloticus: Effects of linolenic acid on non-specific immunity and anti-inflammatory responses in juvenile fish

This study was conducted to investigate the effects of dietary linolenic acid (LNA) on non-specific immunity and anti-inflammatory responses in juvenile Nile tilapia, Oreochromis niloticus. Purified ethyl linolenate was added to the basal diet to formulate seven isoproteic and isolipidic diets containing 0.00, 0.10, 0.32, 0.63, 0.98, 1.56 and 2.04% LNA of dry weight, respectively. All diets contained similar amounts of 18: 2n-6 (0.61% of dry weight) from purified ethyl linoleate. Basal diet without LNA was considered as a control. Fish were fed experimental diets for 10 weeks. The results showed that amounts of LNA as well as eicosapentaenoic acid, docosahexaenoic acid and even arachidonic acid in head kidney macrophages showed strong positive curvilinear relationships with dietary LNA levels. No significant differences were observed in serum lysozyme and superoxide dismutase activities among dietary treatments (P < 0.05). The phagocytic activity of head kidney macrophages increased with the increase of dietary LNA from 0.00 to 0.63% and then decreased as the dietary LNA increased to 2.04% (P < 0.05). Macrophages in fish fed the diet with 0.32% LNA showed the highest respiratory burst activity (P < 0.05). The expression of pro-inflammatory cytokines tumor necrosis factor a (TNF-alpha) and interleukin (IL) 1 alpha in lipopolysaccharide (LPS)-stimulated macrophages of fish fed diets with 0.32-0.63% LNA significantly reduced compared to those of the control group (P < 0.05). In addition, a significant dose-dependent reduction in LPS-induced nitric oxide (NO) production of macrophages was demonstrated by dietary LNA levels. The results suggested that moderate levels of dietary LNA (0.32-0.63% of dry weight) could enhance non-specific immunity and anti-inflammatory responses of juvenile Nile tilapia. Statement of relevance: To our knowledge, this is the first study to provide specific evidence for the anti inflammatory effect of linolenic acid in juvenile tilapia. Moreover, this study helps to further confirm the dietary requirement of linolenic acid for juvenile tilapia. (C) 2015 Elsevier B.V. All rights reserved.