Thermal effects on the blood respiratory properties of southern bluefin tuna, Thunnus maccoyii

Abstract

Thermal effects on the blood respiratory properties of southern bluefin tuna (Thunnus maccoyii) at 10, 23 and 36 degrees C, and at 0.5 and 1.5% CO(2) were investigated. A reversed temperature effect occurred as the oxygen partial pressure required for 50% haemoglobin saturation (P(50)) at 0.5% CO(2) decreased from 2.9 kPa at 10 degrees C to 1.7 kPa at 23 degrees C (apparent heat of oxygenation, DeltaH degrees , =+27 kJ mol(-1)). However, oxygen binding was essentially independent of temperature at warmer temperatures (P(50)=1.7-2.0 kPa from 23-36 degrees C at 0.5% CO(2); DeltaH degrees =-6.5 kJ mol(-1)). Hill's coefficient (n(H)) ranged from 1.3 to 1.6, and there was a large effect of temperature on the Bohr factor (DeltalogP(50)/DeltapH=-1.6 at 10 degrees C and -0.9 at 36 degrees C). This is the first study of whole blood to demonstrate the thermal dependence of DeltaH degrees itself, whereby the oxygen equilibrium curve is more sensitive to temperature in the lowest thermal range examined. We suggest that the functional basis for these observations lies in the necessity to ensure a sufficient oxygen supply to all tissues, including the heart and liver, without suffering from premature or excessive oxygen unloading around the heat exchanger prior to delivery of oxygen to organs and tissues that lie efferent to the exchanger.