Physiological consequences of prolonged aerial exposure in the American eel,Anguilla rostrata: blood respiratory and acid-base status

Abstract

The physiological consequences of prolonged air-exposure on blood respiratory and acid-base properties were examined in the American eel (Anguilla rostrata). Eels displayed a low capacity for aerial gas transfer as indicated by pronounced increases and decreases in arterial CO2 and O2 tensions, respectively. The increase in arterial CO2 tension contributed to severe extracellular acidosis. The decrease in arterial O2 tension, combined with a marked reduction in red blood cell pH and concomitant Bohr and Root effects, caused arterial O2 content to decline to levels that were insufficient to support metabolic requirements, aerobically. Consequently, the rate of anaerobic glycolysis increased during air-exposure as suggested by a gradual elevation of blood lactate levels after 12 h. Increased anaerobic glycolysis and associated ATP hydrolysis and/or degradation of internal ATP stores further depressed blood pH as metabolic acid, produced by these processes, entered the circulation. Unlike other fishes previously examined, red blood cell pH was not regulated preferentially during the extracellular acidosis but simply conformed to the in vitro relationship between red blood cell and whole blood pH. Although capable of surviving prolonged air-exposure, the results demonstrate nevertheless and perhaps not surprisingly that eels, unlike true amphibious fishes that utilize gills or buccal epithelia for gas transfer, are not particularly well-adapted for gas exchange in air but do display an unusual tolerance to hypoxemia.