Blood Gas Relationships in the Rainbow Trout Salmo Gairdneri

Abstract

1. Oxygen dissociation curves were determined using blood from rainbow trout, acclimated for at least 3 weeks to temperatures of 6, 15 and 20°C. Carbon dioxide tensions in the range 0·3-7 mmHg produced both the Bohr and Root effects in the blood. 2. Increasing temperature, Pco2 and hydrogen ions, whether raised individually or together, caused a decrease in blood O2 affinity (increased value for P50). 3. Blood at low temperatures had a higher pH than blood at high temperatures. This is related to the fact that the ionization constant of water is diminished with decreasing temperature. When blood was 50% saturated and Pco2 was 1 mmHg, the pH value was 8·25 at 6°C, 7·83 at 15°C and 7·62 at 20°C. 4. The factors influencing unloading of oxygen from the blood are discussed. To release the same amount of oxygen from blood, a greater change in carbon dioxide tension is required at 6°C than at higher temperatures. 5. The Bohr effect expressed quantitatively (Δ log P50/Δ pH) was -0·54 at 6°C, -0·57 at 15°C and -0·59 at 20°C. These values are similar to those for the blood of many mammals, and are within the range reported for fish, where whole blood has been used.