Temperature-dependence of cardiac output and regional blood flow in rainbow trout, Salmo gairdneri Richardson

Cardiac output, blood flow distribution and regional perfusion were determined in free‐swimming rainbow trout acclimated to 6, 12 and 18°C, using the indicator dilution and microsphere methods. Cardiac output (ml min−1 kg−1) increased linearly with increasing temperature, while circulation time decreased. Blood flow distribution (% of cardiac output) to the spleen, liver, kidney, gall bladder and gastro‐intestinal tract was significantly reduced at 18°C relative to 6°C‐acclimated fish. White muscle received the largest fraction of cardiac output, and blood flow distribution to white muscle increased significantly with increasing acclimation temperature. Blood perfusion (ml h−1 g−1) of various organs and red muscle was not influenced by acclimation temperature, while white muscle perfusion increased with increasing temperature. These results demonstrate physiological adaptation of the cardiovascular system of rainbow trout to changes in acclimation temperature.