Ventilatory Responses of Teleost Fish to Exercise and Thermal Stress

Exercise and thermal stress both markedly raise the oxygen demand of fish. The control of ventilation under these two conditions is apparently quite different and contrasts between species are noteworthy. Under both exercise and thermal stress, changes in respiratory pumping amplitude tend to be greater than changes in ventilatory frequency in most species. Respiratory pump uncoupling during thermal stress is frequently seen in trout but much less so in bullhead catfish or bluegills. In fish that actively ventilate the gills while swimming, the control for this probably depends on swimming muscle reflexes rather than blood humoral factors. This control mechanism may operate in a reverse fashion in fish that use ram-jet ventilation. During recovery from severe exercise and during thermal stress the control of gill ventilation is apparently humoral. Of the possible factors, blood oxygen and possibly also pH are considered to be the most important. Evidence is summarized that suggests the error detector is on the arterial side of the gas exchanger.