Abstract:
The relationship between whole blood-oxygen affinity (P_{50}) and pH-dependent binding (i.e., cooperativity and the Bohr [Φ] and Root effects) was examined statistically under standardized conditions (10.0°C) in four unrelated cold-temperate marine fishes that differ widely in their swimming performance and their expected responses to hypoxia: cod (Gadus morhua), herring (Clupea harengus), mackerel (Scomber scombrus), and plaice (Pleuronectes platessa). An unexpected difference in blood-oxygen affinity was found (herring> plaice> mackerel> cod)), and this was independent of both swimming performance and the predicted low O_{2} response of each species. The ecotype of the four marine species was also unrelated to pH-dependent binding because no difference in the Bohr effect was apparent (Φ varied insignificantly from -0.90 to -1.06), and differences in the magnitude of the cooperative binding reaction were associated only with the presence of the Root effect. Although several reviews propose a generalized link between blood-oxygen affinity and pH-dependent binding, our results advise against overestimating the adaptive functional properties of hemoglobin across unrelated species.
