This study was conducted to clarify the relationship between dietary lipid levels and n-3 highly unsaturated fatty acids (n-3HUFA) contents, and to determine their suitable levels to sustain the normal growth of yellowtail fingerlings, by feeding them with various white fish meal diets contain-ing different amounts of lipid (6-20%) and n-3HUFA (1.4-5.9%).
At the level of 10% lipid, the elevation of the n-3HUFA level from 2.3 to 3.9% reduced growth, and fish fed on a diet containing 3.9% n-3HUFA showed the lowest growth performances. At the level of 15% lipid, good growth and feed efficiency were observed in fish fed on diets containing n-3HUFA from 2.1 to 3.1%, but further elevation of dietary n-3HUFA content resulted in reduced growth. On the other hand, at the level of 20% lipid, growth and feed efficiency improved as the n-3HUFA content increased, reaching a plateau in diets containing n-3HUFA above 3.4%.
Thus the growth of yellowtail fingerlings was influenced by dietary n-3HUFA levels, and the n-3HUFA content in diet was recommended to be increased in proportion to dietary lipid levels to obtain maximum growth. Moreover, it was also found that the upper limit of suitable n-3HUFA level in the diet was approximately 22% of dietary lipid, irrespective of lipid levels, and that the suitable lipid level in the yellowtail diet was estimated to be 15-20% when n-3HUFA was adjusted to a suitable level.