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River stingrays
Ocellate river stingray, Potamotrygon motoro
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Chondrichthyes
Subclass:	Elasmobranchii
Order:	Rajiformes
Family:	Potamotrygonidae
Genera
Paratrygon Plesiotrygon Potamotrygon

River stingrays are Neotropical freshwater fishes of the Potamotrygonidae family (order Rajiformes).

They are native to northern, central and eastern South America, living in rivers that drain into the Caribbean, and into the Atlantic as far south as the Río de la Plata in Argentina. Generally, each species is native to a single river basin, and the greatest species diversity can be found in the Amazon.

River stingrays are almost circular in shape, and range in size from Potamotrygon schuhmacheri, which reaches 25 centimetres (9.8 in) in diameter, to the short-tailed river stingray, P. brachyura, which grows up to 1.5 metres (4.9 ft) in diameter. The upper surface is covered with denticles (sharp tooth-like scales). Most species are brownish or greyish and often have distinctive spotted or mottled patterns, but a few species are largely blackish with contrasting white spots.

They have a venomous caudal sting, and are one of the most feared freshwater fishes in the Neotropical region, sometimes more feared than piranhas and electric eels. However, they are not dangerous unless stepped on or otherwise threatened.

River stingrays are the only family of batoids completely restricted to fresh water habitats; while there are true freshwater species in the family Dasyatidae, for example Himantura chaophraya, the majority of species in this family are saltwater fish.

Species

The taxonomy of the river stingrays is complex and undescribed species remain. At present, there are twenty recognized species in three genera:

• Genus Paratrygon
  • Discus ray, Paratrygon aiereba (Müller & Henle, 1841).
• Genus Plesiotrygon
  • Long-tailed river stingray, Plesiotrygon iwamae Rosa, Castello & Thorson, 1987.
• Genus Potamotrygon
  • Potamotrygon boesemani Rosa, de Carvalho & de Almeida Wanderley, 2008.
  • Short-tailed river stingray, Potamotrygon brachyura (Günther, 1880).
  • Vermiculate river stingray, Potamotrygon castexi Castello & Yagolkowski, 1969.
  • Thorny river stingray, Potamotrygon constellata (Vaillant, 1880).
  • Largespot river stingray, Potamotrygon falkneri Castex & Maciel, 1963.
  • Bigtooth river stingray, Potamotrygon henlei (Castelnau, 1855).
  • Porcupine river stingray, Potamotrygon hystrix (Müller & Henle, 1834).
  • White-blotched river stingray, Potamotrygon leopoldi Castex & Castello, 1970.
  • Magdalena river stingray, Potamotrygon magdalenae (Duméril, 1865).
  • Potamotrygon marinae Deynat, 2006.
  • Ocellate river stingray, Potamotrygon motoro (Müller & Henle, 1841).
  • Red-blotched river stingray, Potamotrygon ocellata (Engelhardt, 1912).
  • Smooth back river stingray, Potamotrygon orbignyi (Günther, 1880).
  • Rosette river stingray, Potamotrygon schroederi Fernández-Yépez, 1957.
  • Potamotrygon schuhmacheri Castex, 1964.
  • Raspy river stingray, Potamotrygon scobina Garman, 1913.
  • Parnaiba river stingray, Potamotrygon signata Garman, 1913.
  • Maracaibo river stingray, Potamotrygon yepezi Castex & Castello, 1970.

References

• "Potamotrygonidae". FishBase. Ed. Rainer Froese and Daniel Pauly. January 2006 version. N.p.: FishBase, 2006.