Taxonomy & naming
Potamotrygon pantanensis was described by Loboda and Carvalho in 2013 from specimens collected in the baia Sinhá Mariana, a tributary of the Cuiabá River near Barão de Melgaço, Mato Grosso, Brazil — the heart of the northern Pantanal. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) places it in the genus Potamotrygon, family Potamotrygonidae, order Myliobatiformes. The family Potamotrygonidae comprises the freshwater stingrays of South America, a group that became isolated in fresh water millions of years ago and has never returned to the sea.
These are elasmobranchs: cartilaginous fish whose skeleton is cartilage rather than bone, making them close relatives of the sharks and the marine rays, not of the bony fishes that constitute all other groups covered in this atlas. The phylogenetic placement is a fact easily overlooked when a small, disc-shaped animal is labelled an 'aquarium fish', but it matters enormously for understanding their biology, care requirements, and conservation.
The species epithet pantanensis is a straightforward Latinisation of 'Pantanal', the vast seasonal floodplain wetland system from which the species is known. No subspecies or recognised populations are currently distinguished.
Morphology
Potamotrygon pantanensis has the characteristic body plan of its family: a nearly circular pectoral disc, strongly flattened for a bottom-dwelling existence, with the eyes and paired spiracles positioned on top of the head and the mouth, nostrils, and five pairs of gill slits positioned on the underside. The disc is the operative dimension for this fish — the tail adds considerably to total length but is not a guide to the animal's bulk or its space needs. Females reach a maximum recorded disc width of approximately 13 in; males are smaller, reaching roughly 10.5 in DW. The skin carries fine tooth-like denticles rather than scales, giving a rough texture to the disc surface.
The tail is moderately long and bears one or more serrated venomous spines near its base — modified dermal denticles sheathed in venom-producing tissue that are shed and regrown periodically. These spines inflict a deeply penetrating, intensely painful wound and must be treated as a serious hazard. Males are readily distinguished from females by the pair of claspers — rod-like copulatory organs formed from the inner edges of the pelvic fins — that are present in males and absent in females, which in turn attain a larger maximum disc width.
Vertebral counts of 118–125 are recorded in the literature, providing one of the internal meristic characters used in its original description. The disc colouration and pattern, while not fully detailed in available sources, is consistent with the genus pattern of irregular markings on a drab ground.
Habitat
Potamotrygon pantanensis is known from the northern Pantanal region of Mato Grosso, Brazil, specifically from the Cuiabá River drainage within the broader Paraná–Paraguay basin. The Pantanal is the world's largest tropical wetland, a seasonally inundated floodplain where the rivers expand enormously during wet season and contract into a network of channels, lakes, and permanent water bodies during the dry season. This highly seasonal hydrological cycle shapes the behaviour and distribution of all resident species, and breeding in the family Potamotrygonidae is known to be linked to flood level in South American rivers.
Like all river stingrays, P. pantanensis is a benthic species — it lives on and in the substrate, burying itself partially in fine sand or silt with only the dorsal eyes and spiracles exposed. It breathes by drawing water in through the spiracles on top of the head rather than through the mouth, an adaptation that allows respiration while buried or while pinning prey to the bottom. The water of the Pantanal's river systems is typically warm and moderately mineralised compared with the acidic blackwaters of the shield rivers to the north; the Cuiabá River carries clear to turbid water depending on season and location.
The species is treated as an endemic of the northern Pantanal; it has not been reported from outside this region, making it a narrow-range species highly sensitive to localised environmental change.
Feeding
Potamotrygon pantanensis is a carnivore, as are all members of the family. River stingrays are benthic hunters that feed on bottom-living and buried animals — aquatic invertebrates including insect larvae, crustaceans, molluscs, and worms, as well as small fishes when available. Prey is detected using the ampullae of Lorenzini, electro-sensory pores distributed across the ventral surface of the disc that detect the weak electrical fields produced by living animals, allowing a buried ray to locate concealed prey with precision. The disc is then pressed over the prey to pin it, and it is worked back to the crushing tooth plates of the mouth.
In an aquarium setting, P. pantanensis would be expected to accept the same carnivorous diet given to other small Potamotrygon species: earthworms, chopped prawn, mussel, whitebait, and other meaty whole or frozen foods presented on the tank floor. As a small-bodied ray relative to larger species in the genus, its appetite and waste load are proportionally reduced, but the water-quality consequences of benthic carnivore feeding remain significant and must be managed with strong filtration and regular water changes.
Mating
Like all elasmobranchs, river stingrays reproduce by internal fertilisation. A male P. pantanensis locates and approaches a receptive female, grips the margin of her disc — often biting at it — and uses one of his paired claspers, the rod-like copulatory organs formed from the modified inner edges of the pelvic fins, to transfer sperm internally. Both claspers are present in males from early in development, making sex determination straightforward by visual inspection. The courtship interaction can be vigorous and the female may carry bite marks on her disc margin for some time.
The flood cycle of the Pantanal is likely relevant to reproductive timing, as in other Potamotrygonidae: mating and birth have been shown in the family broadly to correlate with seasonal water-level changes in South American river systems. There is no pair bond and no enduring relationship between male and female; once mating is complete the two go their separate ways, and any subsequent parental investment falls entirely to the female.
Breeding
Potamotrygon pantanensis is viviparous — it gives birth to live young rather than laying eggs — and nourishes its developing pups inside the uterus by matrotrophic histotrophy. After the small yolk of the egg is used up, the embryos are sustained by a protein- and fat-rich 'uterine milk' (histotroph) secreted by specialised finger-like extensions of the uterine wall (trophonemata), which the pups take up directly. This is the reproductive mode of the entire family Potamotrygonidae, and it allows the pups to grow to a relatively advanced state before birth.
Gestation in the family ranges broadly from roughly three months to over twelve months depending on species and conditions, though specific data for P. pantanensis are not yet published. Litter size across the family ranges from a single pup to over twenty in large species; a small-bodied species like P. pantanensis is likely to produce a modest litter of a few pups. The newborn rays are fully formed and capable of independent feeding from birth. There is no parental care after parturition — the female's investment ends at birth.
This reproductive strategy — slow maturity, long gestation, small litters — means that river stingray populations recover slowly from depletion, a critical point when evaluating the sustainability of harvest for the ornamental trade or other purposes.
In the aquarium
Potamotrygon pantanensis is occasionally encountered in the specialist freshwater stingray trade, though it is far less common than the widespread P. motoro. Its smaller maximum disc width compared to the largest Potamotrygon means the space requirement, while still substantial, is more achievable than for giant species — but even a ray of 12–13.5 in DW needs a tank whose floor area is measured in multiple square metres, with length and width far exceeding the disc diameter. Height is secondary; floor area and the ability to swim and turn naturally is what matters. A deep bed of fine, soft sand is mandatory: river stingrays bury instinctively, and sharp gravel or bare bases abrade the ventral disc and invite infection.
Water quality is the single greatest challenge in keeping any river stingray. These fish are scaleless, with thin, delicate skin, a high metabolic rate, and acute sensitivity to ammonia and nitrite at any detectable level and to accumulated nitrate above low concentrations. They produce a heavy waste load relative to their size. The combination demands heavy-duty biological filtration and large, frequent water changes — there is no substitute. No salt, no copper-based medications, and no aggressive or fin-nipping tankmates are tolerable.
The venomous tail spine is a genuine medical hazard. A stingray wound is intensely painful, can require hospital treatment, and has on rare occasions been fatal. Potamotrygon pantanensis is not a beginner's fish, and it is not appropriate in a household with unsupervised access by children. A number of jurisdictions restrict or require licensing for the keeping of freshwater stingrays. Where legal, captive-bred individuals are strongly preferred over wild-caught stock, both for acclimation reasons and to reduce pressure on a species whose wild range is small and whose IUCN status is Vulnerable.
Conservation
The IUCN Red List assessed Potamotrygon pantanensis as Vulnerable (criterion A2ce) in a 2024 assessment, reflecting concern about population-level decline driven by a combination of threats affecting its restricted range. As a narrow endemic of the northern Pantanal — essentially the Cuiabá River drainage and associated floodplain habitats — it has no buffer of additional range if local conditions deteriorate. Any habitat-level change, sustained harvest pressure, or water-quality degradation in its core zone translates directly into a population-level impact.
The pressures bear down from several directions. The ornamental aquarium trade captures freshwater stingrays from across the Paraná–Paraguay basin, and the rarity and novelty of P. pantanensis make it attractive to collectors; wild-caught animals still dominate the trade. The species is also at risk from gill-net fisheries targeting other species, and rays are routinely killed when encountered because of the perceived danger of the sting. Agriculture and cattle ranching in the Pantanal watershed affect water quality and riparian habitat. All of this acts on a fish that reproduces slowly, with small litters and a long gestation, meaning populations do not recover quickly from elevated mortality.
The family Potamotrygonidae is listed on CITES Appendix III at the proposal of Brazil and Colombia, meaning international trade in specimens must be accompanied by documentation from the exporting country. Brazilian regulations further restrict the export of wild-caught river stingrays. These measures help but do not by themselves ensure sustainability; effective management of P. pantanensis requires monitoring of wild populations in the Pantanal and promotion of captive-breeding programmes to supply the trade with non-wild-caught animals.