Gill potentials in marine teleosts

The transepithelial potentials of a wide variety of species of marine fishes have been measured. Most lie within the range 20-24 mV positive indicating that chloride is actively excreted while sodium is close to passive equilibrium. In most species the permeability to potassium is greater than that to sodium. In marked contrast to most other families, members of the Syngnathidae showed low or negative potentials. super(22)Na flux measurements in Syngnathus acus showed a rate of flux comparable to that in other marine teleosts, indicating that sodium as well as chloride ions must be actively extruded in this species.