Temperature-Induced Changes in the Oxygen Equilibrium Curve of the Blood of the Brown Bullhead, Ictalurus Nebulosus

The affinity of blood for oxygen is dependent on temperature, which would seem to present a disadvantage to those fishes which encounter large seasonal temperature changes. Considering the well-known acclimatory abilities of many fishes, it would seem reasonable to propose the occurrence of seasonal modification of blood oxygen equilibria to compensate for changes in temperature. 2. In Ictalurus nebulosus, blood from one group of fish acclimated at 24 degrees C showed a consistently higher oxygen affinity compared with a group acclimated at 9 degrees C, when measured at the same temperature. This shift, accompanying thermal metabolic acclimation, minimizes the effect of temperature on oxygen affinity. 3. The shift did not persist when dilute solutions of hemoglobin were studied. 4. No changes with acclimation were seen in the multiple hemoglobin pattern nor in blood pH. 5. The erythrocyte, rather than the plasma, appears to be the site of modification. 6. Some large changes in erythrocyte potassium accompanied thermal acclimation, but the relation of this to the shift in oxygen affinity is unknown