Oxygen exchange in a simulated trout gill secondary lamella

The complex blood flow patterns occurring in a trout secondary lamella were computed from a theoretical electrical model consisting of a two-dimensional array of unitary resistances representing the blood channels of the lamella. Estimates of oxygen uptake from water to blood were made by means of the standard conductance equations for oxygen and values from the literature for blood and water PO2's in trout. The results were plotted as contour charts of blood and water PO2, O2 transfer, and blood flow. According to the results of various manipulations of this model, oxygen exchange across a given lamella will be largely unaffected by changes in the overall shape of the lamella. However, the model predicted that oxygen exchange would be greatly reduced if 1) the basal pillar cell channels were denied access to the respiratory water flow, 2) pillar cell contraction were to force blood into the larger-diameter marginal channels, or 3) the blood flow rate were to be increased, regardless of a concomitant increase in water flow. These predictions are discussed in terms of current theories of gas exchange in teleost gills.