Theoretical analysis of respiratory gas equilibration in water passing through fish gills

Abstract

In order to evaluate the significance of diffusion resistance inside the water passing through fish gills for respiratory gas transfer, calculations were performed on simplified gill models of varied shape and flow velocity patterns. The degree of equilibration inefficiency, equivalent to a functional water shunt, was shown to depend upon the shape of the lamellae and on the flow velocity profile. For identical shape of the lamellae and flow velocity profile, the equilibration inefficiency increased with the parameter (b 2· v )/(l 0·d) ( v , mean water velocity; d, diffusion coefficient of gas in water; 1 0, length of the lamellae; b, half distance of the lamellae). By applying the theory to literature data on gill water flow and morphometrics in teleosts, it was estimated that, in basal conditions, about 10%, and with increased gill water flow (hypoxia, activity), about 50% of the respiratory water flow might be functionally shunted, and that about 1 4 of the experimentally determined total O 2 uptake resistance might be attributed to diffusion resistance of gill water.