VENTILATION AND ACID-BASE RECOVERY FOLLOWING EXHAUSTING ACTIVITY IN AN AIR-BREATHING FISH

The effects of exhausting activity in normoxic (P-O2=20.7 kPa) ana hyp oxic (P-O2<2.7 kPa) water on ventilatory, metabolic and acid-base vari ables were examined in spotted gar (Lepisosteus oculatus) to determine the role of the air-breathing organ in supporting active metabolism a nd recovery. The level of aquatic hypoxia used effectively eliminated the gills as a site of O-2 uptake, forcing the fish to respire as a un imodal air-breather. Swimming duration (until exhaustion) was not sign ificantly different in normoxic and hypoxic water. Blood gas, acid-bas e, cardiovascular and ventilatory variables were monitored at interval s from 15 min to 24 h post-exercise. Fish survived exhaustive exercise using a combination of anaerobic metabolism and increased ventilation (aerial and aquatic), despite respiratory and metabolic acidoses, The cardiovascular effects of exercise (heart rate and dorsal aortic bloo d pressure) were minor. The metabolic effects of exercise were similar to those in unimodal water-breathing fish; however, even hypoxic anim als recovered from exhaustive exercise by 24 h, Thus, the results of t his study show that air breathing in L. oculatus allows gar to exercis e to the same extent in normoxic and hypoxic water and enables them to re-establish blood gas and acid-base balance after exhaustive activit y even in hypoxic water.