Taxonomy & naming
Potamotrygon yepezi was described by Castex and Castello in 1970 and is placed by the Catalog of Fishes in the genus Potamotrygon, family Potamotrygonidae, order Myliobatiformes. These are elasmobranchs — cartilaginous fish whose skeleton is built of cartilage, not bone, making them close kin to the sharks and the marine rays rather than to any bony fish. Potamotrygonidae is the only family of stingrays that became fully established in fresh water, and Potamotrygon is its large core genus, distributed across the river systems of South America.
The species was examined in the broader taxonomic revision of Potamotrygon by Rosa (1985), which reorganised several synonyms and placed the genus in its modern form. Shark-References notes that the genus name Elipesurus has historically appeared as a synonym for some Potamotrygon material. The valid name as accepted today is Potamotrygon yepezi Castex & Castello, 1970. The species epithet likely commemorates or refers to the Yepez family or a local geographic or personal name; no formal etymology is recorded in the available sources.
Morphology
P. yepezi has the body plan common to its family: a broadly rounded pectoral disc, flattened for benthic life, with the eyes and paired spiracles set on top of the head for respiration while buried, and the mouth and five pairs of gill slits underneath. FishBase records a maximum disc width of 15.5 in for males and unsexed specimens; larger females may exceed this figure, and the total length including the tail is considerably greater than the disc width alone.
The tail carries one or more serrated venomous spines near its base — modified dermal denticles enclosed in venom-producing tissue, which are shed and replaced periodically throughout the animal's life. The skin surface is covered in small tooth-like denticles rather than true scales. Males are readily identified by their paired claspers, rod-like copulatory organs formed from the inner margins of the pelvic fins; females lack them and typically grow to a larger adult size.
Habitat
Potamotrygon yepezi is a single-drainage endemic, known from the rivers that empty into Lake Maracaibo in northwestern Venezuela. This makes it one of the most geographically restricted of all the river stingrays: the Maracaibo Basin is hydrologically isolated from both the Orinoco and the Amazon systems, and P. yepezi has not been recorded beyond it.
Within that drainage it occupies shallow, turbid, muddy-bottomed channels — the kind of slow or moderate lowland river margin where a ray can lie partly buried in soft substrate with little more than its eyes and spiracles exposed. Water temperatures range from 73–84 °F and pH from 6.0 to 7.0, reflecting the warm, moderately soft freshwater conditions of the region. Like all potamotrygonids it respires by drawing water in through the spiracles on top of the head rather than through the mouth, an adaptation that allows it to breathe while buried and while feeding on the bottom.
Feeding
FishBase records P. yepezi as feeding on insect larvae, consistent with the broadly invertivorous diet typical of Potamotrygon in shallow, muddy-bottomed habitats. The ray hunts on or just beneath the substrate surface, using its flattened disc to pin prey and the electro-sensory ampullae of Lorenzini — pores distributed across its underside — to detect the faint electrical fields of concealed or buried organisms.
In captivity, river stingrays of this size range accept a carnivorous diet of benthic foods: bloodworms, earthworms, prawns, mussel, and similar whole or frozen meaty items offered at or near the substrate. They are strong feeders that produce a substantial bioload, and the tension between their appetite and their extreme sensitivity to their own waste products sets the core challenge of their husbandry.
Mating
River stingrays reproduce by internal fertilisation, as do all elasmobranchs. A male Potamotrygon approaches the female and may bite the margin of her disc — often leaving visible tooth marks — before gripping her and inserting one of his paired claspers to transfer sperm. There is no spawning site, no external eggs, and no nest; the whole of fertilisation and early embryonic development happens inside the female's body.
Courtship in potamotrygonids is tied to the hydrological cycle: reproductive activity tends to be seasonal, rising and falling with the flood pulse that shapes life in South American rivers. There is no pair bond and no involvement by the male beyond mating; the entire remaining investment in the offspring falls to the female.
Breeding
Potamotrygon yepezi is viviparous — it gives birth to live young — and nourishes them by matrotrophic histotrophy. After the small yolk reserve of the egg is consumed, the developing pups are sustained inside the uterus by histotroph, a secretion rich in proteins and lipids produced by vascularised extensions (trophonemata) of the uterine wall, which the embryos take up directly. This 'uterine milk' allows the pups to grow substantially before birth.
Litter size in Potamotrygon typically ranges from 1 to 8 pups, and gestation lasts several months. Pups are born as fully formed, independent miniature rays capable of feeding immediately; there is no parental care after birth. The reproductive biology that makes these rays so remarkable in evolutionary terms — live birth, internal nourishment, small litters — is also the biology that makes them so vulnerable: slow maturity, a long gestation, and modest litter sizes mean that a population cannot recover quickly from overharvest or habitat loss.
In the aquarium
P. yepezi reaches a disc width of 15.5 in and requires an aquarium whose floor area reflects that size — a long, wide tank measured in square metres, where the ray can turn and lie flat without obstruction, matters far more than water height. The substrate must be a deep bed of fine, soft sand; the ray buries regularly, and coarse gravel or bare glass will abrade the disc. Soft to moderately soft, acidic to near-neutral water (pH 6.0–7.0, 73–84 °F) matches the conditions of the Maracaibo drainage.
River stingrays are scaleless and their thin skin is acutely sensitive to dissolved waste; ammonia must be kept at zero and nitrate kept low through powerful filtration and large, frequent water changes. They tolerate no salt and react badly to many common medications — copper is particularly toxic. Tankmates must be entirely peaceful and non-nippy, as any harassment of the disc or tail risks stress and injury. The venomous spine is a genuine hazard: a sting is intensely painful and can require medical treatment, making this species unsuitable for households with children and subject to permit or licence requirements in many jurisdictions. Captive-bred stock, where available, should be strongly preferred over wild-caught animals from a depleted, narrowly endemic population.
Conservation
Potamotrygon yepezi was assessed as Endangered (EN) under IUCN criteria A2cde in December 2024 — a recent and significant finding that reflects genuine population decline driven by a combination of factors. The species is a single-basin endemic with an inherently restricted range; the entire global population is confined to one isolated drainage system, so any threat operating across the Maracaibo Basin affects the species as a whole. FishBase rates it as having very low resilience, with a minimum population doubling time of more than 14 years.
Pressures include habitat loss and degradation within the Maracaibo watershed, capture for the ornamental aquarium trade (which has historically driven significant export of wild potamotrygonids across South America), and the general pattern of persecution that affects venomous species — rays are often killed on sight for their sting. Colombia listed the species on CITES Appendix III in 2016, requiring export permits; illegal trade nonetheless continues to supply demand in Europe, North America, and Asia. The slow reproductive rate that is characteristic of the whole family — small litters, several months' gestation, late sexual maturity — means that populations cannot easily absorb harvest pressure, and any significant decline is difficult to reverse on a human timescale.