Cardiovascular and respiratory changes during heat stress in rainbow trout (Salmo gairdneri).

Numerous studies on the effect of temperature change on fish have been made (see bibliography by Raney & Menzel, 1969). Most of these have been concerned with behaviour, metabolism, reproduction, and lethal limits and have usually involved long-term effects where temperature acclimation becomes an important factor. Relatively little has been done on the physiological effects of rapid changes in temperature. Recently techniques involving measurements from indwelling catheters in the blood vessels and respiratory cavities have been applied to physiological studies in fish (e.g. Holeton & Randall, 1967; Hughes & Roberts, 1970). The latter measured changes in ventilatory and cardiac frequencies in lightly anaesthetized trout during rapid warming. Apparent uncoupling of the buccal and opercular pumps and bradycardia occurred at high temperatures, findings not unlike those noted for trout subjected to hypoxia (Marvin & Heath, 1968; Hughes & Saunders, 1970). Cocking (1959) suggested that high-temperature death in fish might be due to insufficient oxygen being supplied to the tissues. In the present study blood pressure, blood oxygen content, oxygen consumption and respiratory pressures were measured in unanaesthetized trout during warming. The physiological changes taking place shortly before death from heat stress were also examined since the causes of thermal death in fish are still poorly understood (Fry, 1967).