TEMPERATURE AND CO2 EFFECTS ON BLOOD O-2 EQUILIBRIA IN NORTHERN SQUAWFISH, PTYCHOCHEILUS-OREGONENSIS

In vitro blood O2 equilibrium curves were constructed at 9, 1 5, 18, a nd 21-degrees-C from temperature-acclimated northern squawfish, Ptycho cheilus oregonensis. At low Pco2 (<1 mm Hg, 1 mm Hg = 133.32 Pa), P50s generally showed variable increases with temperature from 3.6 mm Hg a t 9-degrees-C to 8.7 mm Hg at 21-degrees-C, leading to whole-blood tem perature effects (DELTAH, kilocalories per mole O2) ranging from a low +4.4 at 15-18-degrees-C to a peak -21.2 at 18-21-degrees-C. High-PCO2 (7.6 mm Hg) conditions decreased blood pH and increased P50s at each temperature (Bohr factor). Bohr factors (PHI) ranged from -0.46 at 21- degrees-C to -0.70 at 18-degrees-C. Considered together, DELTAH and PH I values suggest an optimal temperature range of 15-18-degrees-C for h emoglobin O2 loading and unloading in northern squawfish. Nonbicarbona te buffer values ranged from -10.04 at 21-degrees-C to -14.13 at 9-deg rees-C. Overall, the high O2 affinities and hyperbolic blood O2 equili brium curves of northern squawfish resemble those of other large cypri nids (e.g., common carp, Cyprinus carpio, tench, Tinca tinca, Sacramen to blackfish, Orthodon microlepidotus) indicating a better ability to tolerate hypoxic environments than sympatric rainbow trout, Oncorhynch us mykiss. High northern squawfish blood O2 capacities and PHIs sugges t high aerobic capacity, especially at temperatures <21-degrees-C.