Determination of suitable protein and lipid levels in diets for Pacific bluefin tuna, Thunnus orientalis at grow-out stage

Abstract

Three test diets were formulated using non-enzyme treated fish meal (FM) and fish oil with protein and lipid levels (%) of 55 and 18 (D1), 51 and 22 (D2), and 47 and 26 (D3) to determine the suitable dietary level as well as the utility of non-enzyme treated FM at grow-out stage of Pacific bluefin tuna (PBT), Thunnus orientalis. Raw sand lance, Ammodytes personatus (D4) with 64% protein and 11% lipid was used as the control. Duplicate groups of 100 young PBT (mean weight 82.9 g) were stocked into 6×6×4.5 m³ net cages and reared for 35 days. Although there was no significant difference in mean body weight between D1 and D4, D4 showed significantly higher value than that of D2 and D3 (P<0.05). The survival was significantly higher in fish fed with D1 (59.0%) than that of D4 (47.5%) (P<0.05). Dietary protein/energy ratio and protein content showed strong positive linear correlation with final mean weight. Relative weights of viscera, pyloric caeca and intestine in fish fed with D1-D3 were significantly higher than those of D4 (P<0.05). The increasing level of dietary lipid in D1-D3 resulted in significantly lower retention efficiency than that of D4 (P<0.05). Results suggest that the non-enzyme treated FM can be utilized and dietary level of 55% protein and 18% lipid could improve the growth performance as well as the survival of juveniles PBT at grow-out stage.