Requirement of Eel Anguilla japonica for Essential Fatty Acids

Abstract

Feeding experiments were conducted to determine the EFA requirement of eel by feeding them with various diets containing both 18:2ω6 and 18:3ω3 in different ratios. In addition, the growth effect of ω3HUFA (a mixture of 20:5ω3 and 22:6ω3) was compared with that of 18:2ω6 and 18:3ω3. The fat-free and the EFA-deficient diets resulted in retarded growth and low feed efficiency. Tha addition of either 18:2ω6 or 18:3ω3 to the diets improved growth, 18:3ω3 being the more effective. However, the best weight gain was obtained in the fish receiving a diet containing both 0.5% 18:2ω6 and 0.5% 18:3ω3 and the growth rate was almost comparable to that of the control diet containing a mixed oil of corn oil and pollock liver oil. The addition of ω3 fatty acids, not only 18:3ω3 but also ω3HUFA, to the EFA-deficient diet improved growth rate and feed efficiency and the supplemental effect of 1% ω3HUFA was almost the same as that of 1% 18:3ω3.
Feeding the EFA-deficient diet resulted in raising the levels of the “ abnormal ”polyunsa-turated 20:3ω9 and monoethylenic fatty acid, 18:1. These levels were lowered by both ω6 and ω3 fatty acids. The conversion of 18:2ω6 into 20:4ω6 and 22:5ω6 or 18:3ω3 into 22:6ω3 was inhibited to a certain extent by dietary 18:3ω3 or 18:2ω6, respectively.
Thus, the diet requirement of eel for 18:2ω6 and 18:3ω3, respectively, was found to be around 0.5% of each, or 1% for 18:3ω3.