Overview
The Giant Freshwater Stingray (Urogymnus polylepis), formerly cataloged as Himantura chaophraya, is one of the world’s most colossal freshwater creatures. Native to the great river arteries of Southeast Asia, this prehistoric elasmobranch holds the official world record for the largest documented freshwater fish ever recorded by science, with verified specimens exceeding 660 pounds (300 kilograms). Resting quietly beneath deep river sandbeds, this riverine giant embodies the ancient evolutionary grandeur of freshwater megafauna.
Biology and Physical Characteristics
Urogymnus polylepis features a massive, flattened pectoral disc that is oval-to-circular in outline, ending in a slightly pointed snout. The dorsal surface is covered in fine dermal denticles colored a uniform chocolate-brown or slate-gray, while the ventral underside is immaculate white bordered by a distinctive dark margin. Extending from the base of its disc is a long, slender whip-like tail that can measure nearly twice its body length. Near the base of the tail sits a massive, serrated venomous barb measuring up to 15 inches in length, capable of punching through bone when deployed in defensive reflex.
Behavior and Ecology
A specialized bottom-dweller, the giant freshwater stingray uses sensory electroreceptive pores (ampullae of Lorenzini) peppered across its ventral surface to detect faint bioelectric fields generated by crabs, shrimp, and bottom fish buried under silt. Expanding its disc margins, it generates powerful hydraulic suction to blast sediment away before crushing prey with dense pavements of molar-like teeth. The species reproduces via aplacental viviparity (ovoviviparity), with mothers nurturing a small litter of one to four large pups within the uterus through nutrient-rich uterine secretions (‘uterine milk’).
Conservation and Human Impact
The IUCN assesses Urogymnus polylepis as Critically Endangered, with wild populations plunging across its historical range. Hydroelectric mega-dams built across the Mekong and Chao Phraya rivers block migratory movements and disrupt seasonal river discharges, while agricultural pesticide runoff and industrial pollution induce catastrophic mass die-offs. Accidental entanglement in commercial gillnets and longlines also causes heavy losses. Conservation coalitions in Cambodia and Thailand employ satellite tagging and establish community river sanctuaries to safeguard remaining giant individuals.
Interesting Factoid
In June 2022, fishermen in Cambodia’s Mekong River captured a record-shattering Giant Freshwater Stingray nicknamed ‘Boramy’ (Full Moon) that weighed an incredible 661 pounds (300 kg), officially taking the crown as the biggest freshwater fish ever measured in human history!
Last updated: October 2026