The Effect of Increased Ambient CO2 On Arterial CO2 Tension, CO2 Content and pH in Rainbow Trout

ABSTRACT The effect of exposure of rainbow trout to high and low levels of environmental (water) CO2 tension on blood CO2 and pH was studied. An increase in environmental CO2 caused a rise in the arterial CO2 tension , but the blood-to-water gradient (P1-Pa) remained about the same. Changes in arterial pH were small - about one-third of what would be predicted from the change in if plasma bicarbonate remained constant. There was a corresponding increase in the total CO2 content of the blood which involved an upward shift of the CO2 dissociation curve, and readjustment of the buffering to maintain pH. The results are consistent with the hypothesis that blood CO2 and pH levels are regulated via a chloride-bicarbonate exchange mechanism, rather than by ventilation and diffusive washout of gaseous CO2.