Inorganic ions and pH in the body fluids of Amazon animals

In all but 3 of 16 species of Amazon crustaceans and fishes, the activities of inorganic ions in the blood are 15–27% lower than expected. In most of the fishes, blood pH is higher than expected. In two of the fishes both departures are reversed by adding NaCl or KCl, but not H+, to the medium. Ammonia excretion varies inversely with blood and water salinity, and changes in blood ammonia induced by experimental exposure to air or high salinity can explain the changes in blood pH. Preliminary data suggest that the (Na+ + K+)-ATPase prepared from the gill of one teleost has a higher affinity for NH4+ than K+. It is suggested that at least some of the Na+ absorbed from the medium is exchanged for NH4+, and that binding to the ammonia molecule is responsible for at least some of the reduction of H+ activity in the blood.