Muscle temperature was measured by telemetry in giant Atlantic bluefin tuna whilst the tuna were free-swimming in large pounds. Muscle temperature tended to remain steady at about 24 degrees C; water temperature ranged from 9 to 17 degrees C. Muscle temperature was much less variable than stomach temperature in these fish. Muscle temperature varied less than 3 degrees C whereas stomach temperature varied by as much as 14 degrees C.