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About the Cover
Cover: The unusual stenohaline freshwater stingray Potamotrygon sp. has lost most of the characteristics that are typical of marine elasmobranchs (e.g. high osmolality, urea retention, a functional rectal gland) and displays an ionoregulatory physiology superficially similar to that of freshwater teleosts. Potamotrygon thrives in the ion-poor waters of Brazil's Rio Negro, despite the presence of branchial ion transport systems that exhibit surprisingly low affinity for external sodium and chloride and virtual insensitivity to the ionic composition of the acclimation water. However, ionic permeability is very low, and the ion transporters appear to differ at a mechanistic level from those of freshwater teleosts. See article by Wood, Matsuo, Gonzalez, Wilson, Patrick and Val, pp. 3039-3054. The photograph was taken by Maria Goes de Araujo of the Projeto Potamotrygon-ACEPOAM.
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