Tuna Metabolic Rates Estimated from Energy Losses during Starvation

Metabolic rates were calculated from energy losses over time in fasting, freeswimming tuna (30-50 cm fork length). Water content accurately predicted caloric density measured by bomb calorimetry. A subsample that accurately predicted water and energy content in whole tuna was found. The mean metabolic rate for Katsuwonus pelamis starved < 1 wk was 0.36 kJ·d⁻¹ · g⁻¹ wet mass. Tuna kept for longer periods had lower and less variable swimming speeds and metabolic rates. Mean rates for 1-2 wk of starvation were 0.22 kJ·d⁻¹· g⁻¹ for K. pelamis and 0.18 kJ·d⁻¹ · g⁻¹ for both Euthynnus affinis and Thunnus albacares. For >2 wk of starvation, the mean rates were 0.14 kJ·d⁻¹· g⁻¹ for K. pelamis and 0.12 kJ·d⁻¹ · g⁻¹ for both E. affinis and T. albacares. Our energy-loss estimates of metabolic rate covered the same range as K. pelamis respiration rates. Energy losses in fasting tuna were about twice as high as in fasting cold-bodied fish under equivalent conditions.