Taxonomy & naming
Potamotrygon tigrina was formally described by Carvalho, Sabaj Pérez and Lovejoy in 2011 in Zootaxa (2827: 1–30), with the type locality given as the Río Nanay, upper Amazonas basin, Peru. It is placed by the Catalog of Fishes (Eschmeyer, California Academy of Sciences) in the genus Potamotrygon, family Potamotrygonidae, order Myliobatiformes.
Potamotrygonidae are elasmobranchs — cartilaginous fish whose skeleton is built of cartilage, not bone — making them close relatives of the sharks and marine rays rather than of the bony fishes that make up the rest of the aquarium hobby. They are distinguished from all marine rays by their obligate freshwater biology and from all other freshwater fish by this fundamentally different body plan. Within the genus, the original description notes that P. tigrina is closely related to P. schroederi but is immediately distinguished from all congeners by its conspicuous disc coloration: bright yellow-orange vermiculations on a dark brown to black ground, a pattern unique in the genus. The holotype is a juvenile male; diagnostic characters also include a single angular cartilage and relatively low dorsal tail spines.
The epithet tigrina is Latin for 'tiger-like', referring directly to the bold striped and vermiculate colour pattern of the disc.
Morphology
The tiger stingray shares the body plan of its family: a rounded, nearly circular pectoral disc strongly flattened for life on the substrate, with the eyes and paired spiracles positioned on the dorsal surface of the head and the mouth, nares, and five pairs of gill slits on the underside. The spiracles — paired openings just behind the eyes — allow the ray to draw in water for respiration even when the mouth is pressed against the sand or the animal is buried, a key adaptation for a benthic lifestyle.
The disc's dorsal surface is its most diagnostic feature: a very dark brown to black ground colour overlaid with bright yellow-orange vermiculations (worm-like, branching marks) that cover much of the disc surface, creating the 'tiger' pattern. The tail bears alternating cream and dark bands and carries, near its base, one or more serrated venomous spines — modified dermal denticles sheathed in venom-producing tissue, shed and regrown periodically. The skin is otherwise covered in small tooth-like denticles rather than scales. Sexual dimorphism is present and clear: males carry paired claspers — rod-like copulatory organs derived from the inner margins of the pelvic fins — while females lack them and generally grow larger. Males are known to reach at least approximately 15.5 in disc width at sexual maturity; the species attains at least 27.5 in disc width, with some reports suggesting potentially up to 39.5 in, which would make it one of the largest in the genus.
Habitat
Potamotrygon tigrina is known primarily from the Río Nanay and surrounding drainages of northeastern Peru in the upper Amazon basin — a region encompassing both black- and whitewater river systems. The Nanay itself is a clearwater to blackwater river draining from the Peruvian lowlands, and the species has been recorded across mixed whitewater and blackwater habitats in this restricted area. GBIF records confirm sandy beach associations; the ray is a benthic species of river margins, sandy beaches, and shallow floodplain waters with fine substrate.
Like all river stingrays, P. tigrina prefers warm tropical water. The mixed black- and whitewater context of its range suggests it may encounter a range of chemistry, from moderately mineralised whitewater closer to neutral pH to very soft, acidic blackwater. Pristine water quality is essential: scaleless and sensitive, river stingrays are acutely vulnerable to the organic pollution that inevitably accumulates in slow river margins and in captive systems. The species respires while buried by drawing water in through its spiracles rather than the mouth, an elasmobranch adaptation that allows continuous oxygen uptake while the animal is hidden in the sand.
Feeding
Potamotrygon tigrina is a carnivore and benthic predator, like all members of its family. Basic biology in the field is poorly known owing to the scarcity of specimens, but the family pattern is a diet of bottom-living invertebrates — aquatic insect larvae, crustaceans, molluscs, worms — supplemented by small fishes where available. Prey is detected partly through the electroreceptive ampullae of Lorenzini, a network of jelly-filled sensory pores on the underside of the disc that can sense the faint electrical fields produced by living organisms buried in sand or sediment. The ray pins prey against the substrate with its disc and processes it with the crushing tooth-plates in the mouth.
In captivity, tiger stingrays can be offered meaty, high-protein foods suited to a benthic predator: earthworms, prawn, mussel, squid, and whole frozen foods presented on the substrate. The species is reported to be sensitive and difficult in captivity, and feeding responses are a key indicator of health and water quality in a kept animal.
Mating
River stingrays reproduce by internal fertilisation, as do all elasmobranchs. A male approaches and grips the female, biting the margin of her disc, then inserts one of his paired claspers into the female's cloaca to transfer sperm. Courtship can be vigorous, and disc-margin bite marks on females are commonly observed in both wild-caught specimens and captive groups. There is no spawning site, no external eggs, and no pair bond; the male's involvement ends at mating.
Basic reproductive data are sparse for P. tigrina specifically. The holotype and early specimens are juvenile males, and maturity in males is estimated at approximately 15.5 in disc width based on clasper development. Because the species is narrow-range, poorly represented in museum collections, and sensitive in captivity, detailed observations of mating behaviour are limited. The fundamental elasmobranch pattern of internal fertilisation via claspers is well-established for the family and applies here.
Breeding
Potamotrygon tigrina is viviparous — it gives birth to live young — as are all members of the family Potamotrygonidae. After the small egg yolk is consumed early in development, the pups are nourished inside the uterus by a protein- and fat-rich secretion called histotroph, or 'uterine milk', produced by specialised extensions of the uterine wall. The embryos absorb this directly. This mode, matrotrophic histotrophy, is characteristic of the whole family and allows the pups to grow substantially before birth.
Litter size is not documented for P. tigrina specifically; the family pattern in Potamotrygon is a modest litter — typically a few to around a dozen pups in larger species — born after a gestation of several months. Neonates are fully-formed miniature rays, independent at birth, and receive no parental care afterward. The reproductive biology of river stingrays is inherently slow: small litters, long gestation, and the relatively late age at maturity mean that populations cannot recover quickly from elevated mortality. For a species with as restricted a range as P. tigrina, this slow reproductive pace is a serious conservation concern.
In the aquarium
Potamotrygon tigrina is among the most coveted freshwater stingrays in the aquarium trade and also among the most demanding. Its bold tiger coloration drives strong commercial demand, but the species is reported to be sensitive and difficult under captive conditions, considerably more so than the wide-ranging P. motoro. An adult requires an enormous aquarium with a wide footprint — floor area measured in square metres, several times the disc width in both length and width, with height being the least important dimension. A deep bed of soft, fine sand is not optional: this is a fish that buries itself, and coarse substrate abrades the delicate, scaleless disc.
Water quality must be pristine and maintained with exceptional diligence. River stingrays are scaleless, with thin sensitive skin, a high metabolic load, and acute sensitivity to ammonia and accumulated nitrate — the same animal producing large quantities of waste while being among the most sensitive to it. Heavy biological filtration, generous surface area, and large, frequent water changes are the minimum. No salt should be added; many medications, particularly copper-based treatments, are dangerous. Tankmates must be peaceful and non-nipping; aggressive bottom-dwellers and large cichlids are incompatible. The venomous tail spine is a genuine hazard: a stingray wound causes intense pain, can result in serious injury, and requires medical attention. These animals are emphatically not suitable in households with unsupervised children, and their keeping is restricted or licensed in several jurisdictions. Captive-bred specimens are strongly preferred over wild-caught animals, both for the conservation of wild populations and because captive-bred rays typically acclimate better.
Conservation
The IUCN Red List assesses Potamotrygon tigrina as Endangered under criteria B1ab(iii,v), with the most recent assessment updated in December 2024. The listing reflects a geographically restricted range (known from only two to five localities in northeastern Peru), evidence of continuing habitat degradation, and pressure from commercial collection for the ornamental trade. The species is considered a narrow-range endemic of the upper Amazon; its entire known distribution falls within a relatively small area of the Peruvian Amazon, making any local threat effectively a range-wide threat.
The combination of slow reproductive biology — small litters, long gestation, and late sexual maturity — means that the tiger stingray cannot sustain significant harvest pressure. Removal for the aquarium trade, even at moderate levels, can outpace reproduction in an endemic with so few known localities. Additional threats across its range include habitat modification, deforestation of riparian zones, mercury contamination from artisanal gold mining (widespread in Amazonian Peru), and the broader degradation of Andean-foothill river systems. While P. tigrina is not yet listed on the CITES appendices, the genus Potamotrygon has been the subject of international trade discussions and several range states — Brazil and Colombia among them — have implemented export controls on related species. The restricted distribution of P. tigrina, combined with limited specimen data, makes robust population assessment difficult; better field survey data and strict regulation of the commercial trade are the most urgent priorities for the species' security.