Giant Freshwater Stingray

It is now the record holder. In June 2022, fishers on the Mekong River in Cambodia caught a female giant freshwater stingray that weighed almost exactly 300 kilograms (661 pounds) and measured 3.7 metres from snout to tail; scientists tagged and released it, and it was certified as the largest freshwater fish ever documented, edging out the previous record held by a Mekong giant catfish. The species regularly reaches 200 kilograms or more, and its disc alone can be more than 2 metres across. "Biggest freshwater fish" is a contested title — the beluga sturgeon grows larger but spends much of its life at sea, and the arapaima and Mekong giant catfish are close competitors in pure freshwater — but by the strict record, the giant freshwater stingray holds it.

Very. The giant freshwater stingray carries one of the largest stings of any ray — a barbed, serrated spine that can exceed 35 centimetres, coated in venomous tissue and mounted near the base of a powerful, muscular whip tail. A defensive strike can drive the spine deep into a limb or torso, and there are documented cases of it penetrating the planking of small boats. The wounds are severe — the serrations tear a ragged, heavily bleeding gash, the venom causes intense pain and tissue death, and the spine often breaks off inside. Fatalities have occurred, usually from a strike to the chest or abdomen or from later infection. Researchers handling these rays take great care to control or shield the tail.

Two reasons. First, it lives in large, deep, muddy, turbid rivers where visibility is often only a few centimetres, and it spends the daylight hours buried under a thin layer of sediment with just its eyes and breathing openings showing — so a two-metre ray can be lying on a riverbed that people fish, swim, and boat over without anyone knowing. Second, it is genuinely scarce and getting scarcer. Even dedicated research programmes on the Mekong catch only a handful a year, and the species was not formally described under its current name until the 2000s. Its size, its camouflage, and its rarity together mean most people in its range have never seen one.

It has the classic profile of a species in trouble — it grows slowly, matures late, and produces only a few large pups per litter, so populations replace themselves very slowly and cannot withstand much added mortality. At the same time it faces intense and multiple pressures across Southeast Asia — it is caught deliberately for meat and for the aquarium and curio trade, taken as bycatch in nets and on lines set for other fish, and hit hard by the degradation of its river habitat through dam construction (which blocks movement and alters flow and sediment), sand mining, pollution, and declining water quality. The Mekong is a particular concern, and the species is now a flagship for freshwater megafauna conservation there.