Giant Freshwater Stingray

The Giant Freshwater Stingray (Urogymnus polylepis, formerly placed in Himantura) is among the largest freshwater fish species in the world, with some individuals reportedly reaching disc widths over 2 m and total weights exceeding 250 kg. It inhabits large river systems of Southeast Asia, including the Mekong, Chao Phraya, and Mae Klong basins, as well as parts of Borneo. Despite its enormous size, it remained scientifically poorly described until relatively recently, and much of its biology is still being studied through tagging programs. The species is classified as Endangered, threatened by habitat loss from dam construction, river degradation, and incidental capture in fishing gear.

• Disc: very large, broad, and rounded to slightly oval, uniformly colored
• Color: plain grey-brown to olive above, pale cream to white below, without strong spotting or patterning
• Tail: extremely long and thick relative to disc size, bearing a large serrated venomous spine
• Eyes: small, positioned on top of the head
• Size: disc width regularly exceeding 1.5 m, among the largest of any stingray

Its sheer size combined with plain, unspotted coloration and confinement to freshwater rivers separates it from smaller, patterned marine and reef stingrays.

The Giant Freshwater Stingray lives in large, deep river channels and associated estuaries across mainland and insular Southeast Asia, most notably the Mekong River in Cambodia, Laos, Vietnam, and Thailand, as well as the Chao Phraya and Mae Klong rivers and rivers in Borneo. It prefers deep pools with sandy or muddy substrates, often near river bends, and can tolerate a range of salinities, occasionally entering brackish estuarine reaches. Its dependence on free-flowing, connected river systems makes it highly sensitive to dam construction and habitat fragmentation.

Giant Freshwater Stingrays are bottom-dwelling ambush predators that rest partially buried in sand or mud, feeding on fish, crustaceans, and mollusks detected using electroreception. Despite their massive size, they are generally slow-moving and solitary, occupying deep river pools that serve as refuges. Reproduction is ovoviviparous, with females giving birth to small litters of large, well-developed pups after gestation, though reproductive rates are low given the species' size and slow maturation. As one of the largest predators in its river systems, it plays a significant ecological role, and its populations are closely monitored through tagging and tracking research programs.