Abstract
1. Oxygen dissociation curves of tenth (Tinca tinca) blood were constructed for fish which had been acclimated to 5, 13 or 20°C for at least 3 weeks. 2. Compared to the blood of an active fish such as the rainbow trout tenth blood has a high affinity for oxygen; at 13°C and a PCOCO2 of 2-3 mmHg the blood was half saturated with oxygen at a POO2 of 4 mmHg. 3. Increasing temperature, increasing PCOCO2 and increasing hydrogen ion concentration decreased the oxygen affinity of the blood. 4. At low temperatures the blood had an elevated pH value compared to blood at high temperatures. This is discussed in terms of the temperature dependence of ionization constants, in particular that of water. 5. The Bohr effect and the factors influencing the loading and unloading tensions of oxygen in tenth blood are discussed. The role of the blood in respiration and some properties of fish haemoglobins are also discussed.