N-3 ESSENTIAL FATTY ACIDS IN NILE TILAIA, Oreochromis niloticus: EFFICES OF LINOLENIC ACID ON NON-SPECIFIC IMMUNITY AND ANTI-INFLAMMATOY RESPONSES IN JUVENILE FISH  

This study was conducted to investigate the effects of dietary α-linolenic acid (ALA) 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% ALA 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 ALA was considered as a control. Fish were fed experimental diets for 10 weeks. The results showed that amounts of ALA as well as eicosapentaenoic acid, docosahexaenoic acid and even arachidonic acid in head kidney macrophages showed strong positive curvilinear relationships with dietary ALA 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 ALA from 0.00 to 0.63% and then decreased as the dietary ALA increased to 2.04% (P < 0.05). Macrophages in fish fed the diet with 0.32% ALA showed the highest respiratory burst activity (P < 0.05). The expression of pro-inflammatory cytokines tumor necrosis factor α (TNF-α) and interleukin (IL) 1β in lipopolysaccharide (LPS)-stimulated macrophages of fish fed diets with 0.32-0.63% ALA significantly reduced compared to those of the control group (P < 0.05). In addition, a significant dose-dependent reduction in LPS-induced nitric oxide production of macrophages was demonstrated by dietary ALA levels. The results suggested that moderate levels of dietary ALA (0.32-0.63% of dry weight) could enhance non-specific immunity and anti-inflammatory responses of juvenile Nile tilapia.