The world’s largest freshwater fish, a 13-foot-long, 661-pound stingray, has been discovered in the Mekong River in Cambodia. Scientists say the animal is a hopeful sign for the river, which faces threats from human encroachment and development, damming and climate change, per a statement from FISHBIO, a fisheries and environmental consulting company.
The giant freshwater stingray (Urogymnus polylepis) was caught on June 13 by a local fisherman, who alerted scientists from the Wonders of the Mekong project, a joint Cambodian-U.S. research and outreach initiative.
“When you see a fish this size, especially in freshwater, it is hard to comprehend, so I think all of our team was stunned,” Wonders of the Mekong leader Zeb Hogan tells Jerry Harmer from the Associated Press.
The team heaved the massive fish out of the water using a tarp, then weighed it on industrial scales and fitted it with an acoustic tag so they could track its movements, writes the New York Times’ Jason Bittel.
“The fact that the world’s largest freshwater fish was caught in the Mekong is remarkable,” Hogan tells the Times. “This is a heavily populated region, and the river faces a ton of challenges, including lots of fishing.” In particular, dams built along the river have been disrupting spawning grounds for a variety of species, including stingrays.
Globally, about 70 percent of giant freshwater fish are endangered, Hogan tells the AP. Many of these species have relatively long lives and can take a long time to mature, so if they’re fished before reaching that maturity, they don’t have a chance to reproduce. Many also require large areas to survive and grow. Stingrays take up to four years to reach sexual maturity and are relatively slow-growing for the batoid family of fishes, which includes relatives like sharks.
“In 2020, one of the contenders for the world’s largest freshwater fish, known as the Chinese paddlefish, was declared extinct,” Hogan tells the Times. “That was very sad news, and it had me feeling like we were going to see more extinctions of these big fish, rather than records being broken.” The Chinese paddlefish is another example of a large, slowly maturing animal driven to extinction, reaching sexual maturity around seven or eight years.
The Mekong River, which runs through China, Myanmar, Laos, Thailand, Cambodia and Vietnam, is home to several giant fish species. This particular section—south of Stung Treng in northeastern Cambodia—may be an important breeding ground for the stingrays; four females of the species, including this one, have been caught in the area recently, per the AP. Last month, a group of local fishermen caught a 400-pound female stingray in the same stretch, writes Mongabay’s Carolyn Cowan.
The newly discovered stingray breaks the previous freshwater fish record held by a 645-pound Mekong giant catfish captured in 2005.
“Large fish are bellwethers of the health of freshwater ecosystems worldwide,” Hogan tells Mongabay. “The fish are sending us a message and we need to listen to it.”