Cardiovascular events associated with air breathing in two teleosts, Hoplerythrinus unitaeniatus and Arapaima gigas

Abstract

Cardiovascular events associated with air breathing were investigated in two teleosts, Hoplerythrinus unitaeniatus and Arapaima gigas, in which the air-breathing organs are modified swim bladders. These fish are bimodal breathers whilst in water; they maintain gill ventilation and take periodic air breaths. Cardiac output, blood flow to the air bladder, dorsal aortic blood pressure, and air bladder gas pressure were measured directly in A. unitaeniatus. Dorsal aortic blood pressure and air bladder gas pressure were measured in A. gigas. Both fish were subject to air exposure by draining water from the holding tank. Hoplerythrinus unitaeniatus increased air bladder perfusion following an air breath by redistributing blood flow. There was also a tachycardia after an air breath, but cardiac output did not change significantly at or between air breaths. Preferential perfusion of gill arches 3 and 4 and increased general systemic resistance both probably contribute to produce blood redistribution. During air exposure, H. unitaeniatus demonstrated hyperventilation and heart rate was elevated. In A. gigas in water the mean dorsal aortic blood pressure and heart rate remained constant, which is atypical in comparison with other air-breathing fish.