Largest Freshwater Fish?

ishers and scientists announced this week the catch, and release, of what is likely the world's largest known freshwater giant stingray.

The giant stingray, weighing an estimated 550 to 990 pounds (250 to 450 kilograms) was reeled in on January 28, 2009, as part of a National Geographic expedition in Thailand.

The stringray's body measured 6.6 feet (2 meters) wide by 6.9 feet (2.1) meters long. The tail was missing. If it had been there, the ray's total length would have been between 14.8 and 16.4 feet (4.5 and 5 meters), estimated University of Nevada Biologist Zeb Hogan.

Hogan was in Thailand searching for giant fish as part of the Megafishes Project—an effort to document Earth's 20 or so freshwater giants.

The new find gives Hogan hope that the giant stingray, once overfished, may be more abundant than previously thought. And it may confirm the giant stingray as the heavyweight champ of the Megafishes Project.

"Honestly, we just don't know how much it weighed. But it's clear that the giant stingray has the potential to be the largest freshwater fish in the world," said Hogan, also a National Geographic Emerging Explorer. (National Geographic News is owned by the National Geographic Society.)

"The Thai populations were once considered critically endangered, although with the discovery of new populations the stingray's abundance appears higher than previously believed," added Hogan. The International Union for Conservation of Nature (IUCN) currently lists the freshwater giant stingray as vulnerable.

Last March Hogan found a 14-foot-long (4.3-meter-long) ray near the Thai city of Chachoengsao.

Freshwater giant stingrays are among the largest of the approximately 200 species of rays. They can be found in a handful of rivers in Southeast Asia and northern Australia.

Much is still unknown about the mammoth ray species, including whether or not it can swim out to and survive at sea. The species was first described scientifically only in 1989.

Hogan and his colleagues are still looking for new varieties and populations of the giant stingray.