Meeting Abstract

P1.185  Friday, Jan. 4  Influence of Ambient Temperature on Specific Dynamic Action in Bluefin Tuna GLEISS, A C*; WHITLOCK, R E; DALE, J J; CLARK, T D; BLOCK, B A; Hopkins Marine Station, Stanford University; Finnish Game and Fisheries Research Institute, Helsinki; Hopkins Marine Station, Stanford University; Australian Institute of Marine Science, Townsville; Hopkins Marine Station, Stanford University agleiss@stanford.edu

Bluefin tunas are the most endothermic teleost fish. They have evolved the ability to elevate their muscle, viscera and brain temperature above ambient water temperatures and capture metabolic heat with counter-current heat exchangers. Pacific bluefin tuna ( Thunnus orientalis) studied in captivity have a specific dynamic action (SDA) associated with metabolic rate elevated up to 2.3X routine metabolic rate and a doubling of heart rate in response to feeding. During SDA, the viscera warms as much as 8C° in juvenile Pacific bluefin tuna. Pacific bluefin showed an increased duration of specific dynamic action and heat increment of feeding as temperatures cooled both in captivity and the wild. This suggests four possibilities: a) increased heat conservation, b) increased meal size, c) decreased enzymatic performance, d) decreased cardiac performance and a limited aerobic scope. To examine this, we instrumented captive fish with temperature and acceleration data logging tags to capture information on thermal inertia, swimming speed and body temperature of fish digesting meals at different ambient temperature. Here we report on the physiological limitations to digestive performance in this endothermic fish. Our data are discussed in light of temperature limiting the range of these highly migratory fish.