Giant Stingray Could Be World's Largest Freshwater Fish

The beast of a stingray caught by Zeb Hogan's "Megafishes Project" team, which is conducting an expedition to tag freshwater fishes in southeast Asia with National Geographic. CREDIT: University of Nevada, Reno

As part of a National Geographic expedition, scientists caught what could be the world’s biggest stingray.

The fish was tagged and released in central Thailand on Jan. 28, during the expedition, which seeks to find and protect specimens of the world's largest freshwater fish.

A photo marking the catch was widely circulated along with a rumor that it weighed a whopping 771 pounds. But while the stingray was indeed a heavyweight, its exact weight is unknown.

"While the photo is genuine and there’s no denying that this is a huge stingray, the stingray in the photo was never weighed," said conservation biologist Zeb Hogan of the University of Nevada, Reno. Hogan was the lead researcher on the expedition.

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.

The fish, caught by volunteer angler Ian Welch from a small boat using a rod and reel, will be featured in an upcoming documentary airing on the National Geographic Channel.

Hogan, along with his team of researchers and anglers on site at the time of capture, approximate the fish’s weight to be between 550 and 770 pounds. An even slightly larger fish than the one tagged would almost certainly be a world record freshwater fish, he said.

"In terms of disk width, this is the second largest stingray I’ve seen, the largest was in Cambodia in 2003," Hogan said. "This recent fish was very thick, so it may have weighed more."

"It's clear that this species of giant freshwater stingray has the potential to be the largest freshwater fish in the world," Hogan said. The current record holder for world’s largest freshwater fish is a 646-pound Mekong giant catfish caught by fishermen in northern Thailand in 2005.

After the first catch, the researchers encountered the stingray again, about 4 kilometers away from where they initially caught it.

"Surprisingly, we caught the stingray again four weeks later on Feb. 28," Hogan said.

The find could mean that the ray population is smaller, or less migratory, than originally believed.

Biologists continue to track the big fish’s movements using an array of underwater listening devices designed to detect tagged fish.

Hogan and his team have tagged 18 of this species of stingrays (Himantura chaophraya) as part of the recently established research project on the stingray in central Thailand for the University of Nevada, Reno, the Thai Department of Fisheries, the sport-fishing company Fishsiam and the National Geographic Society sponsored Megafishes Project. This species is listed as vulnerable to extinction by the International Union for Conservation of Nature (IUCN).

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