Blood Gas Relationships in the Rainbow Trout Salmo Gairdneri

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Abstract
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. Increasing temperature, and hydrogen ions, whether raised individually or together, caused a decrease in blood O2 affinity (increased value for P50). 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 was 1 mmHg, the pH value was 8·25 at 6 °C, 7·83 at 15 °C and 7·62 at 20 °C. 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 dioxid tension is required at 6 °C than at higher temperatures. The Bohr effect expressed quantitatively (ΔlogP50/ΔpH) 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.