BLANK, J.M.; FARWELL, C.J.; SCHALLERT, R.J.; MORRISSETTE, J.M.; BLOCK, B.A.; Hopkins Marine Station, Stanford University: Metabolic Rate of the Pacific Bluefin Tuna, Thunnus orientalis

Tunas are teleosts reknowned for their unique thunniform swimming mode, high metabolic rates and exceptional cardiac performance. Among tunas, the bluefin species attain the largest body sizes, inhabit the broadest thermal niches, and maintain the greatest elevation of body temperature. Metabolic rates measured in tropical tunas exceed those of most other teleosts, however, no measurements of metabolic rate in bluefin tuna have been published to date. Experiments are now under way to measure the metabolic rates of Pacific bluefin tuna, Thunnus orientalis, swimming in a swim tunnel respirometer. Preliminary results indicate that bluefin tuna have higher metabolic rates than those of similar sized yellowfin tuna when measured at 20°C. Metabolic rate in bluefin tuna exhibits a U-shaped relationship to swimming speed with a minimum near 1 BL/s. Gross cost of transport shows little change across speeds of 1.0 to 1.8 BL/s. Temperature-dependence of bluefin metabolic rate appears to be exceptionally low and preliminary results indicate that bluefin tuna are truly endothermic fish. Funded by NSF and Monterey Bay Aquarium.