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, mean (± SD, n=6) mass 565±90g, to measure elements of respiratory metabolism and exercise performance. At 19°C, the mean standard metabolic rate (106±48 mgO2·h−1) maximum metabolic rate (555±51 mgO2·h−1) and absolute aerobic scope (449±83 mgO2·h−1) were lower than mass-corrected rates of adult Pacific bluefin, but considerably higher than other active sympatric Mediterranean fishes at similar mass and temperature. The tuna ceased swimming at a speed of 2.0±0.2 bodylengths·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 mgO2·h−1. The results indicate that juvenile Atlantic bluefin tuna are high performance animals with elevated metabolic costs for their lifestyle of ceaseless swimming.