CARDIAC RESPONSES OF FISHES IN ASPHYXIC ENVIRONMENTS

Abstract

1. Cardiac frequencies of fishes that normally expose themselves to asphyxic situations were studied. 2. The grunion and the flying fish displayed pronounced bradycardia upon exposure to air with rapidly regained rate when immersed. 3. The air-inhabiting mudskipper responded to water with a heart slowdown and a speedup in air. 4. The hagfish, which lacks cardioregulative nerves, showed no cardiac frequency compensation when placed in air. 5. Comparison is made with the asphyxial adjustments exhibited by land animals when they swim submerged.