Differences in free amino acid compositions in liver and dorsal white muscle of juvenile Pacific bluefin tuna Thunnus orientalis fed raw fish and artificial feeds

Abstract

To develop a more efficient tuna feed, free amino acid compositions in the liver and dorsal white muscle of juvenile Pacific bluefin tuna Thunnus orientalis fed raw fish (RF) and commercial artificial feeds (AF) were compared. Hatchery-reared juveniles (initial BW, 2 g) stocked in two net cages were fed either of the foods from late July to mid-March, and fish samples for analysis were taken monthly. In the liver, concentrations of taurine were higher in the AF group, but increased in both groups toward autumn while concentrations of other amino acids decreased. In the muscle, histidine was dominant and its concentrations were higher in the RF group whereas concentrations of anserine and carnosine were higher in the AF group. In both the liver and muscle, levels of moisture were higher and those of crude fat lower in the AF group. Daily food intake (% monthly average BW/day) in the AF group was estimated to be as high as in the RF group. These findings suggest that dietary lipid utilization was not efficient in tuna fed the artificial feeds and instead dietary protein was used as an energy source, which resulted in the differences in muscle free imidazole-compound compositions.