The time domains of the ventilatory responses of bowfin (Amia calva) to prolonged hypoxia

Abstract

The acute responses of fish to hypoxia are well established, however the time course for the hypoxic ventilatory response in chronic hypoxia is not well understood. In the present study we assessed the ventilatory and cardiovascular responses of the facultative air breather, Amia calva, to severe hypoxia for 3 days. During prolonged exposure to hypoxia, there was an initial increase in gill breathing frequency, amplitude and total gill ventilation over the first three hours of hypoxic exposure, but this was not sustained. After the initial acute response, there was a decrease in total ventilation that lasted until about 24 hours of hypoxic exposure, when a secondary increase in ventilation started taking place. There was also an immediate bradycardia that was not sustained. These changes were accompanied by changes in the size, and density but not distribution of putative gill neuroepithelial cells (homologous to carotid body glomus cells) after 3 days of hypoxic exposure indicating the importance of these cells in the hypoxic ventilatory response. The time domains seen in gill breathing in Amia are similar to those reported in mammals however the time course of these responses is slower with a ventilatory "roll off" developing in hours not minutes. (funded by NSERC of Canada)