Evaluation of the optimum dietary arachidonic acid level and its essentiality based on growth and non-specific immune responses in Japanese eel, Anguilla japonica

Abstract A feeding trial was conducted to evaluate the optimum dietary level and the essentiality of arachidonic acid (ARA, 20:4n-6) based on growth and non-specific immune responses in Japanese eel, Anguilla japonica . A basal ARA free commercial diet was used as a control, and four other diets were prepared by supplementing 0.3, 0.6, 0.9 or 1.5% ARA. The analyzed ARA concentrations of the diets were 0.00, 0.33, 0.71, 1.06 and 1.65% diet (ARA 0 , ARA 0.33 , ARA 0.71 , ARA 1.06 and ARA 1.65 ), respectively. Triplicate groups of fish (initial body weight, 157 ± 2.5 g) were fed one of 5 experimental diets at a ratio of 4% body weight for 12 weeks. At the end of the feeding trial, final weight, weight gain, specific growth rate and feed efficiency of fish fed the ARA 0.71 diet were significantly higher than those of fish fed the ARA 0 , ARA 0.33 and ARA 1.65 diets ( P 1.65 diet was significantly higher than those of fish fed the ARA 0 and ARA 0.33 diets. However, there were no significant differences in superoxide dismutase activity among fish fed diets ARA 0.71 , ARA 1.06 and ARA 1.65 . Fish fed the ARA 1.06 diet showed significantly higher lysozyme activity than those of fish fed the ARA 0 and ARA 0.33 diets. However, there were no significant differences in lysozyme activity among fish fed the ARA 0.71 , ARA 1.06 and ARA 1.65 diets. Therefore, the optimum dietary ARA level could be greater than 0.71% but less than 0.92%. Also, these results may indicate that dietary ARA could be one of the essential fatty acids in Japanese eel. Statement of relevance The findings showed the essentiality of an appropriate arachidonic acid supplementation level for optimum growth of Japanese eel.