Time domains of the hypoxic cardio-respiratory response in bowfin (Amia calva)

•The hypoxic ventilatory response (HVR) of bowfin to hypoxia was measured.•The HVR of bowfin without access to air exhibited time domains similar to those of mammals.•The HVR of bowfin with access to air did not exhibit time domains.•Bowfin without access to air exhibited a tachycardia during recovery from hypoxia.

The aim of this study was to determine whether time domains exist in the hypoxic ventilatory (HVR) and cardiac responses (HCR) of bowfin (Amia calva), a facultative air breather, exposed to sustained hypoxia (SH) (26 mm Hg at 8 °C or 45 mm Hg at 22 °C). It was hypothesized that time domains would be evident in the HVR and HCR of bowfin when denied access to air during SH, as have been reported in mammals. It was also hypothesized that they would not be present in bowfin with access to air during SH because their oxygen supply should not be limited due to air breathing. Bowfin without access to air during SH exhibited time domains of the HVR and some time domains of the HCR. As hypothesized, bowfin with access to air did not exhibit time dependent changes in the gill breathing, air breathing, or cardiac responses to SH. The extent to which these reflect homologous processes to those underlying time domains in mammals remains to be determined.