An examination of the electroreceptive anatomy in the Southeast Asian freshwater stingray Himantura signifer shows it to consist of "miniampullae" which are intermediate in size between the longer ampullae of Lorenzini that typify marine taxa and the microampullae characteristic of neotropical, freshwater potamotrygonids. The histological structure of each ampullary organ is relatively simple. The integumentary pore represents a simple infolding of epidermis; the canal consists of a lumenal layer of simple to heavily vacuolated cuboidal epithelium, surrounded by a connective tissue tunic. The terminal end of the ampulla supports a limited area of sensory epithelium. On the ventral surface of the fish, miniampullae are concentrated around the mouth, underscoring their significance to feeding mechanisms. Results from our observations on H. signifer suggest alternate mechanisms that might be utilized in modifying marine electroreceptive systems to cope with the constraints of fresh water.