Hemoglobin adaptation for fast and slow water habitats in sympatric catostomid fishes.

The oxygen equilibria of Catostomus insignis hemoglobins are pH dependent. Catostomus clarkii hemoglobins have some components (20 percent) whose oxygen equilibria are independent of pH because the alpha chains have NH(2)-termini that are blocked and the beta chains lack the "usual" COOH-terminal histidine. Since the Bohr effect is normally a beneficial phenomenon, the maintenance of some hemoglobins without a Bohr effect must provide a physiological advantage that is habitat specific. The intrastream ecological preferences of these sympatric catostomids suggest that the hemoglobins without the Bohr effect confer an ecological advantage in a swift water habitat.