Cardiorespiratory responses of the common carp (Cyprinus carpio) to severe hypoxia at three acclimation temperatures.

In vivo measurements of the cardiovascular responses of anoxia-tolerant teleosts to severe prolonged hypoxia are limited. Here, we report the first direct measurements of cardiac output (Q), heart rate (f(H)) and stroke volume during prolonged severe hypoxia (<0.3 mg O(2) l(-1)) in common carp (Cyprinus carpio L.) that had been acclimated to 6, 10 and 15 degrees C. While routine Q and f(H) values varied with temperature under normoxic conditions (Q(10) values of 1.7 and 2.6, respectively), severe hypoxic exposure significantly depressed f(H) and Q to similar minimum values that were largely independent of acclimation temperature (Q(10) values of 1.2). In contrast, the duration of cardiac depression and the subsequent time period during which carp could tolerate severe hypoxia were inversely related to acclimation temperature (24 h at 6 degrees C, 6 h at 10 degrees C, and 2.5 h at 6 degrees C). Likewise, respiration rate during hypoxia showed a temperature dependence. An unusual finding was that cardiorespiratory status partially recovered during the latter stages of severe hypoxic exposure. We conclude that the cardiorespiratory responses to severe prolonged hypoxia in common carp involved a mixture of temperature-independent, temperature-dependent and time domain phases.