Dietary protein and lipid requirements for the Pacific bluefin tuna Thunnus orientalis juvenile

The present trial was conducted to determine the optimum proportion of dietary protein and lipid for juvenile Pacific bluefin tuna (PBT), a carnivorous fish possessing very high culture potentials in the Pacific region. Five test diets, D1–D5, were prepared with varying proportion of protein/lipid 72.8/9.2, 66.8/14.8, 61.9/17.9, 57.2/21.9, 53.3/27.0, respectively, using defatted enzyme treated fish meal and salmon egg oil. Raw sand lance (SL) was used as the control. The feeding trial started with each 200 juveniles of 25 days after hatch per 15 m3 tank, having a mean body weight of 0.26 g. The diets were fed to duplicate groups, 6 times daily upto apparent satiation and reared for 10 days. At the end, growth performance was compared among the treatments. The D3 group showed the highest growth performance in terms of final body weight, specific growth rate and feed efficiency but with similar survival rate to the other groups. Carcass lipid content, and viscera and intestine somatic indices rose with increasing in dietary lipid content. D3 fed fish had increased higher carcass 22:6n−3 and 22:6n−3/20:5n−3 ratio but lowered 14:0, 18:1n−9, 20:5n−3 and ∑n−6 fatty acids as compared with those fed the other diets. These results demonstrated that the artificial formulated diet with 61.9% crude protein and 17.9% lipid could be used in juvenile tuna culture successfully.