Humans regularly catch and eat ocellate river stingrays. They have few predators, although caiman are known to eat these stingrays and it is assumed that large fish may as well. However, its serrated, venomous tail spine serves as an obvious anti-predator adaptation.
Known Predators:
These stingrays can be distinguished from closely related species (such as large spot stingrays (Potamotrygon falkneri)) by the presence of orange to yellow dorsal eyespots, each surrounded by a black ring, with diameters larger than the eyes. Body color is otherwise greyish-brown. They are oval in shape with a robust tail, bearing a venemous spine. Maximum total length has been reported at 100 centimeters and maximum weight at 15 kg, though individuals tend to be much smaller (50-60 cm and under 10 kg). Females tend to be slightly larger than males.
Range mass: 15 (high) kg.
Range length: 100 (high) cm.
Other Physical Features: ectothermic ; bilateral symmetry ; venomous
Sexual Dimorphism: female larger
Information regarding lifespan in the wild is unavailable. These animals are known to survive up to 15 years in captivity.
Range lifespan
Status: captivity: 15 (high) years.
Ocellate river stingrays are habitat generalists of tropical (24°C-26 C) freshwater rivers. As a bethopelagic animal, habitat depth varies with the depths of the rivers they inhabit; studies have found these stingrays at depths of 0.5-2.5 meters in the upper Paraná River, but at depths of 7-10 meters in the Uruguay River. Ocellate river stingrays prefer calm waters with sandy substrate, particularly the edges of brooks, streams and lagoons, where they are often found partially buried.
Range depth: 0.5 to 10 m.
Habitat Regions: tropical ; freshwater
Aquatic Biomes: pelagic ; benthic ; rivers and streams
Ocellate river stingrays have eyes positioned on the dorsal surface of the head and oriented in opposition to one another, giving a nearly 360° field of vision, with little binocular overlap and blind spots directly in front of and behind the head. They have crescent-shaped pupils with dynamic irises that can adjust the pupil's size in response to light conditions. These stingrays have lateral line systems, consisting of subepidermal fluid-filled canals distributed throughout the body, which perceive changes in the surrounding water pressure. They also possess an elaborate electroreceptor system that provides for extremely sensitive perception of low-frequency electrical stimuli and allows for detection of prey that cannot be visually perceived, comprised of subdermal groups of electroreceptive units known as the ampullae of Lorenzini. It is also used for detection of predators and recognition of conspecifics, and sometimes in navigation. Olfaction is a major and well-developed means of perception for these stingrays; their olfactory organs are situated in laterally placed cartilaginous capsules on the top of the head.
Communication Channels: tactile ; chemical ; electric
Perception Channels: visual ; tactile ; acoustic ; chemical ; electric
This species is categorized as "data deficient" by the IUCN Red List of Threatened Species. The status of its population is completely unknown. In many areas, no regulations exist regarding the traffic and/or exportation of freshwater stingrays; an ongoing project in Uruguay is encouraging sport fishermen to return caught stingrays to the water. It may be inferred, from the species' generalist diet and habitat, fairly widespread range, and relatively low demand as a food source, that ocellate river stingrays are most likely not currently a critical conservation concern.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
Ocellate river stingrays are ovoviviparous, with eggs approximately 30 mm in diameter at ovulation. They engage in lipidic histrophy, a mode in which developing young are provided with nutrient-rich secretions within the mother's uterus, providing for far more extensive development than the yolk sac can alone. Most development proceeds isometrically, with the overall body proportions essentially established from birth, but there are a few areas of significant allometric development. Total length relative to disk length decreases continuously throughout development, as does tail length relative to total length. This animal's eyes become less anterior in location and smaller in diameter relative to body size as development proceeds. The most rapid growth occurs early in life, tapering off in later years. Gestation of ocellate river stingrays lasts approximately 6 months in the wild, but has been observed within 3 months in an aquarium environment. From 3-21 pups may be born in a litter and the number of young in a litter is always odd. If caught, pregnant wild females are likely to abort their young.
These stingrays can deliver a painful, venomous sting to humans and other organisms. Reports of incidents have become more common recently, likely due to its recent introduction to regions such as the Paraná River.
Negative Impacts: injures humans (bites or stings, venomous )
Ocellate river stingrays are consumed regularly in the Parano-plata Basin. However, in many regions (such as midwestern Brazil) there is no significant commerce of stingrays for human consumption. Juveniles are considered desirable, and are regularly seen in, the ornamental fish trade.
Positive Impacts: pet trade ; food
Ocellate river stingrays play a role in controlling insect populations through their diet. They serve as hosts to a variety of ecto and endoparasites.
Commensal/Parasitic Species:
Food types consumed depend on age and environment. Shortly after birth, young eat plankton and juveniles add small mollusks, crustaceans, and aquatic insect larvae to their diets. Adults are primarily consumers of fish, including loricariids, Astyanax species, and graceful pimelodellas (Pimelodella gracilis), as well as crustaceans (Palaemonidae sp.). They are also known to eat gastropods (Ampullariidae and Hydrobiidae sp.), aquatic insects (Baetidae, Chironomidae, Elmidae, and Naucoridae sp.), and flying insects (Pyralidae, Corduliidae, Gomphidae, Hydropsychidae, Leptoceridae, and Odontoceridae sp.).
Animal Foods: fish; insects; mollusks; aquatic crustaceans; zooplankton
Plant Foods: phytoplankton
Primary Diet: carnivore (Piscivore , Insectivore , Eats non-insect arthropods, Molluscivore ); planktivore
Ocellate river stingrays are endemic to, and widespread throughout, several South American river systems. Most studies on this species have been conducted in the Brazilian Amazon region, and while its presence has been confirmed in the rivers of other South American nations, such as Uruguay, the details of its distribution outside of the Brazilian Amazon are not fully understood. In addition to the Amazon River basin, this species is found in the Uruguay, Paraná-Paraguay, and Orinoco River basins, including the middle and lower portions of Rio Paraná in midwestern Brazil (where it is the most abundant species of stingray), middle portions of the Río Uruguay, and in the Río de la Plata, Río Pilcomayo, Río Bermejo, Río Guapore, Río Negro, Río Branco, Río de Janeiro and Río Paraguay. This species has recently gained access to many upper regions of the Amazon river basin and other non-native areas due to hydroelectric dams eliminating natural barriers.
Biogeographic Regions: neotropical (Introduced , Native )
Mate location methods have not been studied in this species. Information on mating systems has been observed in a captive population, and may exhibit differences from wild populations. Copulation occurs mainly at night. A male attaches himself to a female by firmly clamping his jaws onto the posterior margin of her disk, sometimes leaving prominent bite marks. Around the time of mating, the lips of the female's cloaca become swollen and bloody, presumably from copulation (this may have given rise to the folk notion that female stingrays menstruate). This species exhibits polygyny, although it has been suggested that a male will only mate every few weeks; in one study, a wild-caught male was housed with two captive-born females and, while he bred with both, fresh bite marks were not seen on both females at once, instead being seen at intervals of at least several weeks.
Mating System: polygynous
The reproductive cycle of this species is triggered and directly influenced by the hydrologic cycle of its river environment, rather than seasonal cues. Gonadal maturation takes 3-4 months and ovarian asymmetry, in which only the left ovary is functional, is a common characteristic. Ocellate river stingrays mate during the dry season, corresponding roughly to June through November. Gestation lasts for 6 months, and birthing occurs during the rainy season, corresponding roughly to December through March. Reproduction appears to follow a cycle in which one litter is birthed each year for three years in a row, followed by a several-year period of reproductive inactivity. Observations suggest that the mechanism of this cycle involves three sets of ova being induced to develop during each reproductive pause, with one set of ova finishing reproduction at the start of each breeding season. These stingrays have 3-21 pups per litter; average litter size is 7 pups and smaller females tend to give birth to fewer young. Young are independent at birth.
It has been suggested that male offspring are slightly more likely in a given litter than females (55% male to 45% females). At birth, young average 96.8 millimeters in length, with female disk diameter averaging 110-135 millimeters and male disk diameter averaging 95-120 millimeters (no data for birth mass is currently available). Age at sexual maturity has not been definitively determined, with estimates varying from 20 months to 7.5 years. Most recent studies report that sexual maturity occurs at a disc width averaging 390 mm in males and 440 mm in females, although earlier research reported sexual maturity at smaller sizes (200-250 mm and 240-320 mm, respectively). The relative length of pelvic claspers is a key indicator of sexual maturity in males, increasing from approximately 5% of total body length as juveniles to approximately 20% as mature adults.
Breeding interval: Ocellate river stingrays breed on a cycle of three years of annual reproduction followed by a several-year period of reproductive inactivity.
Breeding season: Breeding occurs during the dry season (roughly June thorugh November).
Range number of offspring: 3 to 21.
Average number of offspring: 7.
Range gestation period: 3 to 6 months.
Average gestation period: 6 months.
Range age at sexual or reproductive maturity (female): 1.75 to 7.5 years.
Range age at sexual or reproductive maturity (male): 1.75 to 7.5 months.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); ovoviviparous
Females continuously invest in their young during development through the constant provision of nourishment, through lipidic histrophy. Pregnant females in the wild are highly likely to abort fetuses upon capture.
Parental Investment: female parental care ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female)
The ocellate river stingray (Potamotrygon motoro), also known as the peacock-eye stingray or black river stingray, is a species of freshwater stingray in the family Potamotrygonidae. It was the first species to be described in the family and is also the most widespread, ranging throughout much of the Río de la Plata, Amazon, Mearim and Orinoco basins in tropical and subtropical South America.[2] It is sometimes kept in aquaria.[3]
Potamotrygon motoro varies significantly in appearance and morphology over its large range,[4] and a taxonomic review of the Amazonian populations is expected.[2] The taxonomy of the populations in the Río de la Plata Basin was reviewed in 2013, leading to the finding that P. motoro is found virtually throughout (absent from the Paraná Basin upriver from Itaipu Dam), but also that there are two additional members of this species complex: P. amandae (widespread in Río de la Plata Basin) and P. pantanensis (northern Pantanal).[2] Two highly distinctive Amazonian types completely lack black-edged yellow-orange spots: The so-called "mantilla ray", CD4, in Peru and adjacent parts of Brazil, and the similar but paler CD5 from rivers near Marajó. Both CD4 and CD5 co-occur with normal variants of P. motoro.[4][5] In 2019, they were described as a new species, P marquesi.[6]
Currently recognized members of the species complex found elsewhere are P. boesemani (Corantijn River; P. motoro absent),[7] P. jabuti (mid and upper Tapajós Basin; P. motoro in the lower),[8] and P. ocellata (lower Amazon Basin), but the last may be a synonym of P. motoro.[9]
Potamotrygon motoro can grow up to 50 cm (1.6 ft) in disc width, 1 m (3.3 ft) in total length,[10] and 35 kg (77 lb) in weight.[11] Its disk is roughly circular in shape, and its eyes are raised from the dorsal surface. The dorsal coloration is typically beige or brown, with numerous yellow-orange spots with dark rings. Its exact color, and the arrangement and size of the spots can vary significantly, both from individual to individual and depending on location. Three primary types have been identified in the Amazon basin, but each of these include a number of subtypes (two additional main types now are considered a separate species, P. marquesi).[4][6] The two main Amazonian types, informally known as CD1 and CD2, are found throughout much of the Amazon (except most of the Rio Negro basin) and they often occur together.[4] Those from the Río de la Plata Basin and Mearim River resemble CD1.[4] Individuals from the Rio Negro and Orinoco basins (which are connected by the Casiquiare canal) are similar to each other and informally known as CD3, but differ from P. motoro elsewhere.[4][5] Some individuals of CD3 have spots near the rim of the disc that are connected, forming a chain-like pattern.[5] However, the "marbled" type is generally only reported from the Orinoco basin, including the Ventuari River.[12]
Ocellate river stingrays are sometimes kept in captivity, with requirements similar to other members of Potamotrygon.[3] It is one of the most popular species of freshwater stingrays, but requires a very large tank.[13]
The ocellate river stingray (Potamotrygon motoro), also known as the peacock-eye stingray or black river stingray, is a species of freshwater stingray in the family Potamotrygonidae. It was the first species to be described in the family and is also the most widespread, ranging throughout much of the Río de la Plata, Amazon, Mearim and Orinoco basins in tropical and subtropical South America. It is sometimes kept in aquaria.
