Oxygen Uptake and Transport by the Rainbow Trout During Exposure to Carbon Monoxide

Abstract

1. Rainbow trout, brown trout and pike were exposed to 5% carbon monoxide which was sufficient to combine with over 90% of their haemoglobin. 2. Trout tested at 10 and 15°C did not survive exposures to carbon monoxide longer than 30 min, but those tested at 5°C survived exposures of up to 3 h. Even at 5°C the trout were weakened and unable to stay upright. 3. The respiratory responses of trout exposed to 5% carbon monoxide at 5°C for 30 min were examined in detail. 4. The trout responded to carbon monoxide with an increase in the flow of blood and water past the gills. As a result the mean partial pressure gradient of oxygen from water to blood across the gill membrane was increased. In spite of these changes oxygen uptake fell by 40%. 5. An increase was observed in heart rate and blood pressure in both the ventral and dorsal aorta of CO-exposed fish. 6. There was a drop in the oxygen diffusing capacity or transfer factor of the gills of CO-exposed trout. 7. Although the fish were rendered anoxic there was no bradycardia, suggesting that this reflex response depends upon either environmental or arterial PO2 and not upon arterial oxygen content. 8. The observed responses to carbon monoxide may be a result of either anoxia, anoxaemia, reduced pH, or a combination of these factors