The Amazonian Freshwater Stingray (Potamotrygon laticeps)

Freshwater stingrays of the Amazon River and its associated basins belong to a unique family of cartilagionous fish known as the Potamotrygonidae.  This family is comprised of about 25-30 species, and unlike all other cartilaginous fish, these stingrays have lost the ability to retain urea in their body fluids.  This is an adaptation to minimize the osmotic gradient associated with a freshwater existence, and, therefore, these species have much lower urine flows than its closely related "cousin", the Atlantic stingray.

Despite their abundance in the Amazon River, there is suprisingly little known about their general biology. In fact, there is still considerable confusion about their taxonomic status and phylogenetic realtionship to other stingray species.  Interestingly, they are thought to have evolved from a common ancestor to modern Dasyatid stingrays, which have a well established ability to handle freshwater environments.  Therefore, our studies on the relativley recently established freshwaterAtlantic stingraypopulations in the St. Johns River, FL may provide valuable insights into the early evolution of the Potamotrygonidae.

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