Stingrays are diverse cartilaginous fish, known as elasmobranchs, characterized by their flattened bodies and whip-like tails. They inhabit various aquatic environments, including oceans, coastal waters, and freshwater river systems. This extensive distribution has resulted in approximately 200 known species, ranging widely in size and shape. While many rays are modestly sized, some species reach colossal proportions, ranking them among the largest fish globally.
The Giant Freshwater Stingray
The largest known species of stingray is the Giant Freshwater Stingray, scientifically classified as Urogymnus polylepis. It holds the record as the world’s largest stingray and one of the largest strictly freshwater fish on the planet. This species belongs to the Dasyatidae family, known as whiptail stingrays, characterized by their elongated tails. Its classification was complex, having previously been known by the synonym Himantura chaophraya. The name Urogymnus polylepis was confirmed based on the earliest published scientific description from 1852. This ray is distinguished from other large rays, such as oceanic manta rays, because it is a true bottom-dwelling stingray of the Dasyatidae family.
Metrics of the Largest Ray
The Giant Freshwater Stingray is primarily measured by its disc width. Verified specimens have reached up to 2.2 meters (7.2 feet) across, with larger individuals confirmed in the Mekong and Chao Phraya Rivers.
The largest verified individual weighed 300 kilograms (660 pounds), establishing it as the largest freshwater fish ever documented. Reliable reports from local fishermen suggest some individuals may reach between 500 and 600 kilograms (1,100 to 1,300 pounds). The total length, measured from snout to the tip of its whip-like tail, can reach at least 5.0 meters (16.4 feet). The long tail contains a single, serrated, venomous spine that can measure up to 38 centimeters (15 inches) in length.
Geographic Range and Diet
This colossal ray is unique among large species for its preference for a freshwater habitat, specifically the large river systems and associated estuaries of Southeast Asia and Borneo. Its range includes major waterways like the Mekong River, the Chao Phraya River, the Nan, and the Mae Klong Rivers, primarily in Thailand and Cambodia. This environment of large, often murky rivers and estuaries contrasts sharply with the marine habitats of most large ray species. The species is a bottom-dwelling predator, favoring areas with a sandy or muddy substrate where it can easily bury itself.
The diet of the Giant Freshwater Stingray consists primarily of benthic organisms, including small fishes, crustaceans, and various invertebrates. To find its prey, which is often buried beneath the sediment, the ray relies on a sophisticated sensory system. Like other elasmobranchs, it possesses electroreceptive organs called the ampullae of Lorenzini. These organs allow the ray to detect the faint electrical fields generated by the muscle movements of its hidden prey, ensuring successful hunting even in the turbid waters of its riverine home.