Xingu Freshwater Stingray, Polkadot Stingray, White-blotched River Stingray.
A large freshwater stingray with a thick, sub-circular disc that is very slightly longer than wide. Small lobe visible on tip of snout. Eyes large and bulging. Spiracles large; length approximately 3x eye length. Nostrils thin. Nasal curtain skirt-shaped with a fringed posterior margin. Mouth with 5 oral papillae.
Disc covered in denticles; more densely grouped towards centre. Pelvic fin posterior margins level with, or shorter than disc margin. Tail broad based, shorter than disc width, with well developed dorsal and ventral finfolds. 3 or more irregular rows of small thorns dorsally on tail. Origin of first caudal sting anterior to mid tail.
Dorsum blackish-brown or charcoal with many widely spaced large white or yellowish spots with darker yellow, beige, or light grey outer rings. Spots usually smaller towards disc margin. Ventrum mostly dark except around mouth and underside of snout. Small white spots usually present around disc margin.
Maximum disc width 72cm. Disc width at birth unknown.
Tropical freshwater rivers. Prefers rocky river bottoms.
South America. Confined to the Xingu River in Pará and Mato Grosso states. Also recorded from the Curuá and Iriri Rivers; both of which are tributaries of the Xingu.
Despite occurring in a large river basin, the polkadot stingray has a relatively restricted range (limited to the Xingu River Basin), and serious impacts in this region may result in population declines.
Habitat loss/degradation involving the development and expansion of agriculture, livestock, ongoing gold mining, fisheries and logging are a threat to this species. Water contaminants originating mainly from agricultural, domestic, sediment, sewage and solid wastes, as a consequence of this development, are also considered threats for P. leopoldi.
Inadequate land management and deforestation, mainly in the Xingu River headwaters and some of its tributaries, are significantly increasing and could bring serious impacts to the entire basin.
Geological characteristics of the Xingu River favour the building of dams throughout the basin and potentially represent a threat to this species; however, it is uncertain how P. leopoldi populations will be affected by this impact. Genetic isolation is likely to take place if the proposed dams of the Belo Monte Hydroelectric Complex are built in the near future.
Human settlement, tourism and recreation often lead to persecution (killing freshwater stingrays due to fear of sting injuries).
This species is seldom used as a food source but is captured as bycatch (mainly by hooking, netting, entanglement and occasionally by poisoning) in other target species fisheries.
Juveniles are captured for the international ornamental fish trade and at present this activity is regulated by an export quota system that must be correctly enforced by the environmental and export related national agencies. It is important to note that captures for ornamental purposes represents an important socio-economic activity for riparian residents in this region.
Historically, severe droughts (associated with the El-Niño phenomenon) in some small tributaries of the Xingu river have caused high mortality (Charvet-Almeida, pers. obs.).
Charvet-Almeida, P., Rosa, R.S. & Pinto de Almeida, M. 2009. Potamotrygon leopoldi. The IUCN Red List of Threatened Species 2009: e.T39403A10226180. https://dx.doi.org/10.2305/IUCN.UK.2009-2.RLTS.T39403A10226180.en. Downloaded on 09 March 2021.
Viviparous with trophodermic nutrition. Relatively fecund. 4-12 pups per litter.
The polkadot stingray feeds mostly on freshwater snails and crabs.
Reaction to divers
Unknown but probably difficult to approach.
There is no infrastructure for diving in the Xingu River but the river is said to be relatively clear. The Xingu is famous among aquarists for its wide variety of colorful fishes that the locals catch for export into the aquarium trade. The collectors catch small fishes by hand with a mask and snorkel and quick reflexes so the visibility must be pretty good.
The Volta Grande rapids near the town of Altamira marks the lower limit of the Xingu freshwater stingray’s range, so flying into Altamira and hiring a boat driver to take you snorkeling upstream is probably your best shot of finding this species.
Bear in mind that this ray prefers rocky areas often where there are constrictions and fast water, so snorkeling in their favorite environment will not be an easy task. Also the enormous new dam downriver from the city has changed the depth, speed, and width of the Xingu River. This will inevitably affect all of the species that live in the river. And finally, mining in the area is slowly poisoning the entire ecosystem so it may be wise to find out more about the river’s toxicity before you stick your head in.
Personally, if I get the chance, I’m going 🙂
Henle’s Freshwater Stingray Similarly patterned but distinguishable by browner dorsum with yellow/beige spots, and less rows of thorns on the tail.