Whole Blood–Oxygen Binding Properties of Four Cold-Temperate Marine Fishes: Blood Affinity Is Independent of pH-Dependent Binding, Routine Swimming Performance, and Environmental

The relationship between whole blood–oxygen affinity (P50) and pH-dependent binding (i.e., cooperativity and the Bohr [F] and Root effects) was examined statistically under standard-ized conditions (10.0C) in four unrelated cold-temperate ma-rine 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 1 plaice 1), and this was independent of both swimmingmackerel 1 cod performance and the predicted low O2 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 (F 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 be-tween blood-oxygen affinity and pH-dependent binding, our results advise against overestimating the adaptive functional properties of hemoglobin across unrelated species