It depends on what you mean by “freshwater.” If you mean a fish that lives its entire life in fresh or brackish water, the largest reliably measured specimen is a giant freshwater stingray (Urogymnus polylepis) caught in Cambodia’s Mekong River in 2022. It weighed about 300 kg (661 lb) and measured 3.98 m (13 ft) from snout to tail, with a disc width of 2.2 m (7 ft 2 in). The ray, named Boramy, was released with a tracker.
Why the answer depends on the definition
Some sources use “freshwater fish” broadly for fish associated with rivers and lakes, even if they migrate to brackish or marine waters. The U.S. Geological Survey, for example, calls the beluga sturgeon the world’s largest freshwater fish. But beluga sturgeon move between freshwater and marine or brackish habitats, so they do not meet the stricter standard of spending their whole lives in fresh or brackish water. Guinness World Records excludes fish that migrate to sea from its freshwater record category.
Under that whole-life definition, the giant freshwater stingray holds the largest reliably measured specimen record. The distinction matters: it separates a documented individual from broad claims about how large a species may grow.
How big was the record stingray?
Guinness World Records lists Boramy, caught in Cambodia’s Mekong River on June 13, 2022, at approximately 300 kg (661 lb), 3.98 m (13 ft) long including the tail, and 2.2 m (7 ft 2 in) across the disc. The weight and measurements describe one captured specimen, not a typical adult or a proven maximum for the species.
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Scientists confirmed the weight, measured the ray at almost four metres, then released it with an acoustic tag. Zeb Hogan, a fish biologist and leader of the Wonders of the Mekong project, said: “In 20 years of researching giant fish in rivers and lakes on six continents, this is the largest freshwater fish that we’ve encountered or that’s been documented anywhere worldwide.” (University of Nevada, Reno, June 21, 2022.)
How it compares with other giant freshwater fish
These figures describe different kinds of evidence. The stingray and Mekong giant catfish figures are measured record specimens; the other maximums below are WWF species-level estimates published in 2010, not verified records of individual fish.
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| Fish | Whole-life freshwater status | Measured specimen or reported maximum | River or range context |
|---|---|---|---|
| Giant freshwater stingray (Urogymnus polylepis) | Yes, under the strict fresh-or-brackish definition | 300 kg (661 lb) measured record specimen; WWF estimated up to 600 kg and 5 m | Mekong and other Southeast Asian rivers |
| Mekong giant catfish (Pangasianodon gigas) | Yes | 293 kg (646 lb) measured specimen in 2005; WWF estimated up to 350 kg and 3 m | Mekong Basin |
| Beluga sturgeon (Huso huso) | No; migrates between freshwater and marine or brackish habitat | Called the largest freshwater fish by the USGS’s broader wording; no comparable measured-specimen figure established here | Russia and Caspian–Black Sea systems |
| Arapaima (Arapaima gigas) | Yes | WWF estimated up to 200 kg and 4.5 m | Amazon Basin |
| Alligator gar (Atractosteus spatula) | Yes | WWF estimated up to 137 kg and 3.05 m | Mississippi River Basin |
The previous reliably measured strict freshwater record was a 293 kg (646 lb) Mekong giant catfish caught in Thailand in 2005; it measured 2.7 m. Boramy’s measured weight was about 7 kg greater. WWF’s estimates of up to 600 kg and 5 m for giant freshwater stingrays are possible species-level maximums, not evidence that a stingray of that size has been reliably weighed and measured.
Sources: Guinness World Records, giant freshwater stingray record; Guinness World Records, Mekong giant catfish record; U.S. Geological Survey FAQ; WWF report on giant freshwater fish.
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Why the record matters for the Mekong
The giant freshwater stingray is threatened by overharvesting and pollution, and WWF lists it as Vulnerable in its report. WWF lists the Mekong giant catfish as Critically Endangered, citing pressures including overharvesting, habitat loss, pollution, and fisheries.
Releasing Boramy with an acoustic tag allowed researchers to track the fish and identify important habitat. The University of Nevada, Reno said this work was intended to help improve protections for the river and the communities that depend on it. The record is remarkable for its size, but it also highlights the importance of keeping the Mekong’s river habitat viable for giant fish.
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