Downstream pH Changes in Water Flowing Over the Gills of Rainbow Trout

Abstract

We investigated the pH of interlamellar water of trout (Salmo gairdneri) by following changes in the downstream pH of expired water using a stopped-flow method. As water flowed over the gills of control fish, there was a significant decrease in water pH. Acetazolamide added to the water increased the CO2 disequilibrium, while carbonic anhydrase (CA) eliminated the CO2 disequilibrium relative to control water. Mucus excreted by the fish was found to contain CA activity by the pH-stat technique. We conclude water acidification is due to the conversion of excreted CO2 to HCO3- and H+ at the gill surface.