The influence of temperature and activity on certain cardiovascular and respiratory parameters in adult sockeye salmon was studied. Cannulae were implanted in the dorsal aorta and buccal cavities of fish which were forced to swim in a tunnel-type respirometer until they fatigued. Three groups of fish were acclimated and tested at 5, 15, and 22°C respectively. Pressures recorded from the dorsal aorta and buccal cavity gave information about heart rate, blood pressure, pulse pressure, ventilation rate and pressures in the buccal cavity before, during and after the fish were fatigued by swimming. Hematocrit data revealed the blood oxygen capacity of these fish, to be approximately 9 vols %. Knowledge of the blood oxygen capacity, heart rate and the metabolic rates of adult sockeye at various temperatures and levels of activity allowed calculation of stroke volume and cardiac output by the Fick principle. During successively greater swimming activity heart rate and blood pressure rose in all three test groups while ventilation rate was highly variable. Calculated stroke volume and cardiac output increased markedly and it is suggested that the peripheral resistance of the vascular system diminished during exercise. The increase in heart rate during exercise is thought to be related to a release of vagal tone or possibly, to the presence of circulating catecholamines. Elevated dorsal aortic pressure during activity was undoubtably the result of elevated cardiac output. Since dorsal aortic pressure did not increase in accordance with the increases in oxygen uptake observed during activity it is suggested that peripheral resistance decreases in the face of elevated cardiac output. Post-exercise ventilation rate approached resting levels within one hour after fatigue but heart rate and buccal pressure remained above resting levels. High post-exercise heart rates and buccal pressures were believed to be evidence for the presence of an oxygen debt. Blood pressures fell below resting levels in the 15 and 22°C test groups following fatigue and remained low one hour after fatigue. These low pressures may indicate that vasodilation of peripheral vessels had occurred to facilitate flushing of the muscles with blood and aid in the elimination of oxygen debt. Temperature appeared to directly influence heart rate of both quiescent and active fish. Higher acclimation and test temperatures produced higher heart rates than lower acclimation and test temperatures. Presumably temperature influences heart rate by acting directly on membrane phenomena in the myocardium. No cardiac failure was observed in sockeye, even at 22°C during severe exercise. Routine and active oxygen uptake increased with temperature but the rate of increase of active oxygen uptake decreased with temperature - possibly because of the low availability of oxygen in warm water. Temperature appeared to directly influence the ventilation rate of quiescent fish. Higher temperatures were accompanied by high ventilation rates, undoubtably as a result of increased routine metabolic rate at high temperatures and scarcity of oxygen in warm water. / Science, Faculty of / Zoology, Department of / Graduate