THE INFLUENCE OF TEMPERATURE UPON THE COMBINATION OF OXYGEN WITH THE BLOOD OF TROUT,

Abstract

Various species of fish possess blood with different characteristic ability for combining with oxygen. These differences appear to fit the blood of each species for the transport of oxygen under special conditions. In three closely related species of trout the characteristics of oxygen combination are similar at the low CO2 tension characteristic of arterial blood. The effect of rising temperature upon the combination of oxygen with the blood in vitro of Salvelinus fontinalis, Trutta trutta, and Trutta iridea is to diminish the oxygen affinity. At 15° their blood is half saturated at 17, 17, and 18 mm. tension of oxygen respectively, and changing temperature increases the oxygen tension required for half saturation about 1 mm. per degree. This situation prevails when the tension of CO2 is about 1 mm., and only at lower temperature does the blood of rainbow trout become distinguishable from the other two in requiring slightly greater oxygen tension for half saturation. CO2 greatly decreases the affinity of the hemoglobin for oxygen. The limit of the effect of CO2 is reached at about 60 mm., and at that tension at 15° the hemoglobin is only half saturated. Raising the temperature diminishes the degree of oxygen saturation in the presence of CO2. When the CO2 tension is 10 mm., half saturation with oxygen requires about twice the tension of oxygen needed in the absence of CO2. The curves representing change in oxygen affinity with temperature when the CO2 tension is 10 mm. are different in position or slope for each of the three species. The differences are large enough to fit the blood of each species for oxygen transport under different conditions. The erythrocytes of trout blood may swell 25 per cent when the CO2 tension is increased from one to 10 mm. The swelling is observed in the blood of several species of fish having hemoglobin which is sensitive to CO2. The CO2 dissociation curves of the three trout are essentially alike and vary in the same manner with temperature. The difference observed in the blood of these three species would apparently provide different conditions for unloading oxygen in the tissues, and the change of unloading conditions with temperature is peculiar to each species of trout. Only at temperatures above 20° would aeration at the gills normally be restricted.