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Family of cartilaginous fishes

River stingrays or freshwater stingrays are Neotropical freshwater fishes of the family Potamotrygonidae in the order Myliobatiformes, one of the four orders of batoids, cartilaginous fishes related to sharks. They are found in rivers in tropical and subtropical South America (freshwater stingrays in Africa, Asia and Australia are in another family, Dasyatidae). A single marine genus, Styracura, of the tropical West Atlantic and East Pacific are also part of Potamotrygonidae. They are generally brownish, greyish or black, often with a mottled, speckled or spotted pattern, have disc widths ranging from and venomous tail stingers. River stingrays feed on a wide range of smaller animals and the females give birth to live young. There are more than 35 species in five genera.

They are native to tropical and subtropical 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. A few generalist species are widespread, but most are more restricted and typically native to a single river basin. The greatest species richness can be found in the Amazon, especially the Rio Negro, Tapajós, and Tocantins basins (each home to 8–10 species). The range of several species is limited by waterfalls. These are S. schmardae from the tropical West Atlantic, including the Caribbean, and S. pacifica from the tropical East Pacific, including the Galápagos. While there are true freshwater species in the family Dasyatidae, for example Urogymnus polylepis, the majority of species in this family are saltwater fish.

Members of Potamotrygonidae are predators and feed on a wide range of animals such as insects, worms, molluscs, crustaceans and fish (even spiny catfish). The family includes both species that are diurnal and species that are nocturnal. Depending on exact species, the gestation period is 3 to 12 months and there are between 1 and 21 young in each litter. The breeding cycle is generally related to flood levels. There are generally one or two stingers, and they are periodically shed and replaced. They are some of the most feared freshwater fishes in the Neotropical region because of the injuries they can cause. In Colombia alone, more than 2,000 injuries are reported per year. Freshwater stingrays are generally non aggressive, As a consequence injuries typically occur when bathers step on them (injuries to feet or lower legs) or fishers catch them (injuries to hands or arms).

Accidents occur when the rays are stepped on or when the fins are touched, the defensive behavior consists of turning the body, moving the tail and introducing the stinger into the victim. Generally, stingers are inserted into the feet and heels of bathers and the hands of fishermen. Initial symptoms include severe pain, erythema and edema, then necrosis occurs which results in sagging tissue in the affected area and forms a deep ulcer, which develops slowly. Systemic complications include nausea, vomiting, salivation, sweating, respiratory depression, muscle fasciculation and seizures. Once the stinger is torn during penetration into the skin, it can break and cause dentin fragments to be retained in the wound. The stinger can cause laceration, which results in secondary infection, usually caused by Pseudomonas and Staphylococcus. If the stinger reaches internal organs, it can be fatal.

Freshwater stingrays are often caught by hook and line and as bycatch in trawls. In the Amazon, Paratrygon and certain Potamotrygon are the most caught species and the first is the most sought. In the Río de la Plata region, the meat of P. brachyura is particularly prized and locally the species is called raya fina (fine ray). Freshwater rays weighing less than are generally discarded, but have a low survival rate.

The status of most species is relatively poorly known, but overall it is suspected that river stingrays are declining due to capture (for food and the aquarium industry) and habitat loss (mainly due to dams and pollution from mining).

[[File:Potamotrygon castexi. jpg|thumb|Some freshwater rays are threatened by dams, but Potamotrygon falkneri was able to spread to the upper Paraná basin due to the Itaipu Dam In contrast, dams threaten some species such as P. magdalenae by isolating populations and preventing gene flow, and others such as P. brachyura generally avoid lentic habitats, including the reservoirs created by river impoundment. Other primary exporters of wild caught freshwater stingrays are Colombia and Peru. A level of illegal exports also occur, It has been suggested that all members of the family should be included on Appendix III, with Paratrygon and a few Potamotrygon species on Appendix II.