One Earth’s “Species of the Week” series highlights the flagship species of each of the 844 unique ecoregions contained within Earth’s bioregions.
Traveling through the Amazon, one is expected to see various creatures as a biodiversity hotspot. One species in its vast freshwater systems, however, is surprising. Far from the ocean is the ocellate river stingray (Potamotrygon motoro) with its unique polka-dot pattern and diet that keeps pest populations in balance.
Flourishing in freshwater
Also known as the peacock-eye stingray or black river stingray, ocellate river stingrays are most notable for the numerous yellowish-orange spots with dark rings against their grey or brown bodies that resemble eyes. Coloration varies in the species depending on location in the river system.
Oval in shape, these stingrays typically measure 50 centimeters (1.6 ft) in width and one meter (3.3 ft) in length. The largest recorded weighed 35 kilograms (77 lb), but the average weighs between 10-15 kilograms (22-33 lb). Females tend to be bigger than males.
Preferring calm waters with sandy riverbeds, ocellate river stingrays are often found partially or fully buried in the summer months to stay cool. In the rainy season, when jungle floors flood, they can be seen swimming through the trees and roots.
Sensory overload evolution
Like other stingray species, ocellate river stingrays have a serrated, venomous tail that serves as protection. Yet, perhaps their most fascinating feature is their sight. With eyes positioned on the top of the head, they have a nearly 360° field of vision.
Distributed throughout their body is a lateral line system, where fluid-filled canals act as a water pressure gauge. Ocellate river stingrays also have an extremely sensitive electroreceptor system, which gives them the ability to perceive low-frequency electrical currents from hidden creatures.
So, if the ocellate river stingray cannot see prey, they can feel them. Their sense of smell is highly functioning too, with well-developed olfactory organs placed on the top of their head.
With such an array of senses, ocellate river stingrays can prey on a variety of life regardless of how clear or murky the rivers or streams of the Amazon might be. They consume fish, mollusks, crustaceans, and zooplankton.
The most important part of their diet, though, is eating mass amounts of insects. In this jungle ecosystem, the ocellate river stingray plays the role of a pest controller, balancing the populations of aquatic, flying, and insect larvae.
Rather than seasonally, ocellate river stingrays breed based on the hydrologic or water cycle of the river systems. Partners mate every three years during dry spells, resulting in 3-21 pups per litter.
While the young are independent at birth, mothers provide nourishment as they develop in utero. Called lipidic histrophy, nutrient-rich secretions are made to the growing fetuses, similar to how mammals give milk to their young.
Help protect their home
While the species is categorized as data deficient in conservation status, the home of ocellate river stingrays is constantly threatened by human development and the impacts of climate change. The most effective way to protect this remarkable species is by safeguarding its habitat.
A variety of vetted programs in the One Earth Project Marketplace provide on-the-ground solutions to solving the duel issues of the climate crisis and biodiversity loss. Supporting conservation efforts in the Amazon region will help preserve the home of ocellate river stingrays.Explore the One Earth Project Marketplace