Theory of CO2 Exchange in Trout Gills*

Abstract

1. A computer simulation of countercurrent CO₂ exchange in fish gills was constructed to examine effects of variations in blood and water flow rates. 2. CO₂ output was sensitive to both blood and water flow rates, contrary to experimental data. 3. Various explanations of the contradiction are discussed, including patterns of gill perfusion and possible shunting of blood. 4. A simplified version of the model was also used to demonstrate extreme sensitivity of CO₂ efflux to variations of the residence time of blood in the gills. 5. Data from the literature on reaction rate constants for the CO₂/carbonate/ bicarbonate system are summarized, and the importance of some of these reactions is examined.