Swimming respirometry provides insights into the physiological energetics of juvenile Atlantic bluefin tuna Thunnus thynnus

Swimming respirometry was performed on juvenile (age 0+) Atlantic bluefin tuna, mass 565±90 g (mean±s.d., n=6), to measure elements of respiratory metabolism and exercise performance. At 19°C, the mean standard metabolic rate (106±48 mg O2 h-1) maximum metabolic rate (555±51 mg O2 h-1) and absolute aerobic scope (449±83 mg O2 h-1) were lower than mass-corrected rates of adult Pacific bluefin, but considerably higher than values in other active sympatric Mediterranean fishes at similar mass and temperature. The tuna ceased swimming at a speed of 2.0±0.2 body lengths s-1 (BL s-1). Video analysis revealed that the juvenile tuna cruised spontaneously at 3.1±0.6 BL s-1 (n=8) in their rearing tank, significantly faster than achieved in the tunnel. Extrapolation of respirometry data to 3 BL s-1 estimated a routine metabolic rate for swimming of over 650 mg O2 h-1. The results indicate that juvenile Atlantic bluefin tuna are high performance animals with elevated metabolic costs for their lifestyle of ceaseless swimming.