The dependence of normal arterial blood pH on sodium concentration in teleost fish

Abstract

Data were compiled on mean pH of arterial blood drawn from cannulated blood vessels of unrestrained fish. In 16 teleost species, mean pH at 15°C (in fish breathing water) shows a negative correlation with plasma Na+ concentration. This accords with the hypothesis that homeostatic mechanisms evolve in such a way as to maintain an optimum local pH at certain unidentified surface sites on cell membranes, these bearing a constant net density of fixed negative charge. The correlation is like one previously found in amphibians and reptiles, but the pH (at 15°C) for a given Na+ concentration is generally higher in teleosts. Possible explanations for this difference are discussed