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Factors influencing gas exhange in the rainbow trout (Salmo gairdneri) Holeton, George F.


A study of factors affecting gas exchange at the gills of rainbow trout during hypoxia was made. Techniques for implanting cannulae in the buccal and opercular chambers, the dorsal aorta, and the ventral aorta are described. The responses of afferent and efferent blood and water pressures, Po₂, PCo₂, pH, and the hematocrit of efferent blood were made while the unanaes thetized free swimming trout was in a sealed respirometer. The fish were allowed to consume the oxygen in the respirometer to produce conditions of hypoxia. Determination of oxygen uptake and a knowledge of the solubility of oxygen in blood and water allowed indirect estimation of ventilation volume, cardiac output and stroke volume of the heart. With this knowledge, inferences on the function of circulatory and respiratory mechanisms during hypoxia were drawn. The rainbow trout possesses a number of homeostatic mechanisms which augment oxygen uptake during hypoxia. It was found that the trout could maintain a fairly uniform oxygen uptake in environmental oxygen tensions as low as 30 to 50 mm Hg„ The major homeostatic responses to hypoxia affecting oxygen uptake were: an increase in ventilation volume, an increase in the functional capacity of the blood, and an apparent vascular shunting of blood closer to the surface of the respiratory epithelium. No significant increase in cardiac output was observed. Since there was a pronounced bradycardia with hypoxia the stroke volume was apparently increasing. The role of the bradycardia, which has usually been associated with a reduction in cardiac output, is not clear. Possible reasons and functions of the bradycardia are discussed.

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