The interaction between O2 and CO2 movements during aerobic exercise in fish.

In resting rainbow trout, 99% of the total CO2 excreted across the gills consisted of bicarbonate (HCO3-) dehydrated to CO2 in the red cell. This value decreased to 93% during exercise, the remainder being excreted as molecular CO2 which existed in the pre-branchial blood. HCO3- dehydration consumes a proton which can be supplied from hemoglobin (Hb) through its buffer capacity or the Haldane effect. Bohr proton release from Hb upon oxygenation is maximal between 50 and 100% of Hb saturation, consistent with observations made in tench blood. At low swimming speeds, when venous blood O2 content (CvO2) was high, there was a small but insignificant acidosis as blood passed through the gills, indicating a greater release of protons than could be consumed by HCO3-. At higher swimming speeds, when CvO2 was low, there was a significant alkalosis in the arterial blood relative to the venous blood, indicating that fewer protons were released upon oxygenation than HCO3- ions were dehydrated to CO2. The disproportionate release of Bohr protons over the range of Hb-O2 saturation in the blood at the gills limits HCO3- dehydration during greater work loads, conserving the HCO3- buffer capacity of the blood and tissues.