Effect of air breathing on acid-base and ion regulation after exhaustive exercise and during low pH exposure in the bowfin, Amia calva

To explore a potential conflict between air breathing and acid-base regulat ion in the bowfin (Amia calva), we examined how individuals with access to air differed from fish without air access in their response to acidosis. Af ter exhaustive exercise, bowfin with access to air recovered significantly more slowly from the acidosis than fish without air access. While arterial blood pH (pH(a)) of fish without air access recovered to resting levels by 8 h, pH(a) was still significantly depressed in fish having access to air. In addition, Pco(2) was slightly more elevated in fish having air access th an those without it. Fish with access to air still had a significant metabo lic acid load after 8-h recovery, while those without air access completely cleared the load within 4 h. These results suggest that bowfin with access to air were breathing air and, consequently, were less able to excrete CO2 and H+ and experienced a delayed recovery. In contrast, during exposure to low pH(a) air breathing seemed to have a protective effect on acid-base st atus in bowfin. During exposure to low pH water, bowfin with access to air developed a much milder acidosis than bowfin without air access. The more s evere acidosis in fish without air access was caused by an increased rate o f lactic acid production. It appears that enhanced O-2 delivery allowed air -breathing bowfin to avoid acidosis-induced anaerobic metabolism and lactic acid production. In addition, during low pH exposure, plasma Na+ and Cl- c oncentrations of fish without air access fell slightly more rapidly than th ose in fish with air access, indicating that the branchial ventilatory chan ges associated with air breathing limited, to some degree, ion losses assoc iated with low pH exposure.