Fig. 5. Visceral temperatures of bluefin tuna in the respirometer. (A) Visceral (black) and ambient water temperature (gray) data were logged at 4 s or 8 s intervals by archival tags implanted in the peritoneal cavity of the fish prior to the experiment and recovered post-mortem. Swim speed was held constant at 1.0 BL s^–1 throughout the experiment. Thermal inertia is evident as a time lag between changes in ambient and visceral temperatures. (B) Visceral thermal excess (Tx) of bluefin tuna swimming in the respirometer. Steady-state Tx was calculated as the difference between visceral and ambient temperatures of fish swimming at constant speeds of 1.0 BL s^–1 following equilibration to the designated ambient temperature for at least 2.5 h. Temperature data were logged at 4 s or 8 s resolution by archival tags implanted in the peritoneal cavity prior to experiments. Values shown are mean ± s.d. for N=3 bluefin tuna (N=2 at 25°C).