Appearance of cuboidal cells in relation to salinity in gills of Fundulus heteroclitus, a species exhibiting branchial Na+ but not Cl− uptake in freshwater

Fundulus heteroclitus (killifish) is a model organism for ionoregulatory studies, particularly because of its opercular epithelium, although the gills are the major sites of ion exchange. Whereas Na+ and Cl− are excreted through the gills in seawater (SW), the killifish is unusual in taking up only Na+ and not Cl− at the gills in freshwater (FW). We describe morphological changes in the branchial epithelium following transfer from an …