The Atlantic bluefin tuna Thunnus thynnus (ABFT) is an extremely valuable marine fish, a pelagic predator with physiological adaptations to a lifestyle of ceaseless swimming, notably partial endothermy and obligatory ram ventilation. Very little is known about ABFT energetics but, by comparison to ‘normal’ teleosts, they are expected to have elevated standard and routine metabolic rates (SMR and RMR) and aerobic metabolic scope (AS), and high aerobic swimming performance. We used swim tunnel respirometry to investigate this in age 0+ juveniles (mass 550g, forklength 30cm) held at 19 °C. The tuna did not enjoy the tunnel, they lost equilibrium and became agitated below 1.4 bodylengths per second (BL s-1), refused to swim faster than 2.2 BL s-1, and had their highest metabolic rates when agitated. Their SMR was about 1.5 times those of other Mediterranean fishes at similar sizes and temperatures, whereas their AS was two to threefold higher. Video analysis of the juveniles in their rearing tank revealed they were actually cruising spontaneously at speeds between 2.5 and 3.5 BL s-1. Extrapolation of respirometry data to 3 BL s-1 indicated an RMR about fourfold higher than direct measures, by tank respirometry, in other Mediterranean species. These preliminary observations would confirm longstanding predictions about the comparative energetics of ABFT but more work is clearly needed and some is ongoing.