Biggest Freshwater Fish Ever Recorded Found In Cambodia's Mekong River

After getting a heads up from local fisherman the night before, a team of scientists from the Wonders of Mekong research project helped snag, tag, and measure the ray before it was released back into the river on June 14, according to FISHBIO whose scientists were also at the scene.

The female giant freshwater stingray (Urogymnus pol­ylepis) was found to weigh in at 300 kilograms (661 pounds) and measured 2.2 meters wide by 4 meters long (7 foot 2 inches by 13 feet 1 inch) from snout to stinger.

This weigh-in proved she was the largest freshwater fish on record, beating the previous record held by a Mekong giant catfish (Pangasianodon gigas) captured in 2005 that weighed 293 kilograms (645 pounds).

The small tag was inserted at the base of the ray’s tail with a small surgical incision. This will gently beam back acoustic signals to 36 retrievers along the Mekong and other nearby rivers that will be able to track the movement and migration of the animal.

This colossal species can be found lurking across many of the large rivers and estuaries of Southeast Asia and Borneo. While its sting is covered in toxic mucus that can pierce bone, it’s generally considered to be a gentle giant and rarely attacks humans unprovoked. 

Like many giant fish of Southeast Asia, the giant freshwater stingray is in trouble. Under the IUCN Red List of Threatened Species, the species is considered endangered with extinction after becoming increasingly threatened by pollution, climate change, human development, and overfishing. 

Many Mekong fish species take lengthy migrations as part of their life cycles to access different floodplains, deep pools, and flooded forests – which is why the tag recently attached to this big beauty is so important. Little is known about where and when particular species embark on their treks, but researchers are desperate to find out so they can learn how to protect these environments and, in turn, their inhabitants.

"Big fish globally are endangered. They're high-value species. They take a long time to mature. So if they're fished before they mature, they don't have a chance to reproduce," Zeb Hogan, Wonders of the Mekong leader from the Department of Biology at the University of Nevada in Reno, told NPR. 

"A lot of these big fish are migratory, so they need large areas to survive. They're impacted by things like habitat fragmentation from dams, obviously impacted by overfishing. So about 70 percent of giant freshwater fish globally are threatened with extinction, and all of the Mekong species."

"The fact that the fish can still get this big is a hopeful sign for the Mekong River,” Hogan added.