The effect of progressive hypoxia on respiration in the dogfish (scyliorhinus canicula) at different seasonal temperatures Available to Purchase

Dogfish were acclimated to 7, 12 or 17°C and exposed to progressive hypoxia at the temperature to which they had been acclimated. During normoxia, the Q₁₀ values for oxygen uptake, heart rate, cardiac output and respiratory frequency over the full 10°C range were: 2·1, 2·1, 2·1 and 2·5 respectively. Increased acclimation temperature had no effect on cardiac stroke volume or systemic vascular resistance, although there was a decrease in branchial vascular resistance, pH_a and ⁠.

Progressive hypoxia had no effect on heart rate or oxygen uptake at 7°C, whereas at 12°C and 17°C there was bradycardia, and a reduction in O₂ uptake, with the critical oxygen tension for both variables being higher at the higher temperature. Cardiac stroke volume increased during hypoxia at each temperature, such that cardiac output did not change significantly at 12 and 17°C. Neither pH_a nor changed significantly during hypoxia at any of the three temperatures.

The influence of acclimation temperatures on experimental results from poikilotherms is pointed out. Previously-published results show quantitative differences.

The significance of the present results with respect to the functioning and location of oxygen receptors is discussed. It is argued that as the metabolic demand and critical oxygen tension of the whole animal are increased at high acclimation temperatures the same must be the case with the oxygen receptor. This would raise the stimulation threshold and could account for the bradycardia seen during hypoxia becoming manifest at higher values of and the acclimation temperature is raised.