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COMPARATIVE AND EVOLUTIONARY PHYSIOLOGY

Circulatory limits to oxygen supply during an acute temperature increase in the Chinook salmon (Oncorhynchus tshawytscha)

¹Faculty of Land and Food Systems, University of British Columbia, Vancouver, Canada; ²Department of Zoology, University of Gothenburg, Gothenburg, Sweden; ³Department of Zoology, University of British Columbia, Vancouver, Canada; and ⁴Department of Forest Sciences, University of British Columbia, Vancouver, Canada

Submitted 29 May 2008 ; accepted in final form 28 August 2008

This study was undertaken to provide a comprehensive set of data relevant to disclosing the physiological effects and possible oxygen transport limitations in the Chinook salmon (Oncorhynchus tshawytscha) during an acute temperature change. Fish were instrumented with a blood flow probe around the ventral aorta and catheters in the dorsal aorta and sinus venosus. Water temperature was progressively increased from 13°C in steps of 4°C up to 25°C. Cardiac output increased from 29 to 56 ml·min^–1·kg^–1 between 13 and 25°C through an increase in heart rate (58 to 105 beats/min). Systemic vascular resistance was reduced, causing a stable dorsal aortic blood pressure, yet central venous blood pressure increased significantly at 25°C. Oxygen consumption rate increased from 3.4 to 8.7 mg·min^–1·kg^–1 during the temperature increase, although there were signs of anaerobic respiration at 25°C in the form of increased blood lactate and decreased pH. Arterial oxygen partial pressure was maintained during the heat stress, although venous oxygen partial pressure (Pv_O2) and venous oxygen content were significantly reduced. Cardiac arrhythmias were prominent in three of the largest fish (>4 kg) at 25°C. Given the switch to anaerobic metabolism and the observation of cardiac arrhythmias at 25°C, we propose that the cascade of venous oxygen depletion results in a threshold value for Pv_O2 of around 1 kPa. At this point, the oxygen supply to systemic and cardiac tissues is compromised, such that the oxygen-deprived and acidotic myocardium becomes arrhythmic, and blood perfusion through the gills and to the tissues becomes compromised.

blood pressure; blood respiratory properties; cardiac output; hematocrit; hemoglobin; heart rate; blood plasma; rate of oxygen consumption; oxygen equilibrium curves; Pacific salmon; stroke volume; vascular resistance

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