Suitable protein and lipid levels in diet for fingerlings of yellowtail

Two feeding experiments were conducted to determine suitable dietary protein and lipid levels for fingerlings of yellowtail by feeding them with various white fish meal (and casein) diets containing different levels of protein (CP: 35-55%) and lipid (CL: 6-20%). In both experiments, the growth rate and feed efficiency were higher in fish fed on diets con-taining around 50% CP than those fed on diets with 45% CP, irrespective of the lipid levels. The best growth was obtained in fish fed on a diet containing 50% CP with 15% CL, when the n-3HUFA level was fixed at 2.1%. On the other hand, at levels of 42 and 52% CP, the feed performances in fish fed on a diet containing a CL of more than 15% were inferior to those in fish fed on 10% CL regardless of n-3HUFA content in the diet. Furthermore, a lower growth rate was observed in fish fed on a moist pellet although the dietary CP level (CP: 63% on a dry matter basis) was the highest of all the experimental diets. These results indicated that not only CP and CL levels but also n-3HUFA contents in the diet affect the growth of yellowtail fingerlings. It was also suggested that the suitable protein and lipid levels in the diet for yellowtail fingerlings are around 50 and 15-20%, respectively, at a level of 2.1% n-3HUFA.