Routine metabolic rate of southern bluefin tuna ( Thunnus maccoyii)

Abstract

Routine metabolic rate (RMR) was measured in fasting southern bluefin tuna, Thunnus maccoyii, the largest tuna species studied so far (body mass = 19.6 kg (± 1.9 SE)). Mean mass-specific RMR was 460 mg kg − 1 h − 1 (± 34.9) at a mean water temperature of 19 °C. When evaluated southern bluefin tuna standard metabolic rate (SMR) is added to published values of other tuna species, there is a strong allometeric relationship with body mass (423 M 0.86, R 2 = 0.97). This demonstrates that tuna interspecific SMR scale with respect to body mass similar to that of other active teleosts, but is approximately 4-fold higher. However, RMR (not SMR) is most appropriate in ram-ventilating species that are physiologically unable to achieve complete rest. Respiration was measured in a large (250,000 l) flexible polypropylene respirometer (mesocosm respirometer) that was deployed within a marine-farm sea cage for 29 days. Fasted fish were maintained within the respirometer up to 42 h while dissolved oxygen dropped by 0.056 (± 0.004) mg l − 1 h − 1 . Fish showed no obvious signs of stress. They swam at 1.1 (± 0.1) fork lengths per second and several fed within the respirometer immediately after measurements.