Temperature and CO2 Effects on Blood O2 Equilibria in Northern Squawfish, Ptychocheilus oregonensis

Abstract

In vitro blood O 2 equilibrium curves were constructed at 9, 15, 18, and 21 °C from temperature-acclimated northern squawfish, Ptychocheilus oregonensis . At low (<1 mm Hg, 1 mm Hg = 133.32 Pa), P 50 s generally showed variable increases with temperature from 3.6 mm Hg at 9 °C to 8.7 mm Hg at 21 °C, leading to whole-blood temperature effects (Δ H , kilocalories per mole O 2 ) ranging from a low +4.4 at 15–18 °C to a peak −21.2 at 18–21 °C. High- (7.6 mm Hg) conditions decreased blood pH and increased P 50 s at each temperature (Bohr factor). Bohr factors (Φ) ranged from −0.46 at 21 °C to −0.70 at 18 °C. Considered together, Δ H and Φ values suggest an optimal temperature range of 15–18 °C for hemoglobin O 2 loading and unloading in northern squawfish. Nonbicarbonate buffer values ranged from −10.04 at 21 °C to −14.13 at 9 °C. Overall, the high O 2 affinities and hyperbolic blood O 2 equilibrium curves of northern squawfish resemble those of other large cyprinids (e.g., common carp, Cyprinus carpio , tench, Tinca tinca , Sacramento blackfish, Orthodon microlepidotus ) indicating a better ability to tolerate hypoxic environments than sympatric rainbow trout, Oncorhynchus mykiss . High northern squawfish blood O 2 capacities and Φs suggest high aerobic capacity, especially at temperatures <21 °C.