Effect of water calcium, copper, and silver on branchial Na permeability in a characid and cichlid fish.

We tested the hypothesis that water Ca is involved in control of branchial Na permeability in low pH tolerant convict cichlids and black neon tetras. We measured Na efflux in water with different Ca concentrations during exposure to low pH, silver, and copper, at levels which are known to stimulate Na efflux. For convict cichlids at pH 7.