A group of Cambodian fishermen caught quite a surprise earlier this month: a massive Mekong giant catfish, the first one seen in the country in a year.

Caught near Phnom Penh, the fish was nearly seven feet long and weighed an estimated 200 to 250 pounds (90 to 114 kilograms), says Zeb Hogan, a fish biologist at the University of Nevada, Reno who examined and tagged the fish.

“It wasn’t that big for a Mekong giant catfish, but it was still larger than any catfish caught in North America over the past century,” says Hogan, who is also a National Geographic Explorer and the host of Nat Geo WILD’s Monster Fish show.

WATCH: National Geographic fellow Zeb Hogan helps release a rare monster catfish in the Mekong River near Phnom Penh, Cambodia. Video: Stefan Lovgren; Photo: University of Nevada, Reno

The largest known catfish in North America was a 143-pound (65-kilogram) blue cat caught in North Carolina in 2011. But that’s dwarfed by the grizzly-bear sized Mekong giant catfish caught in Thailand in 2005, which weighed 646 pounds (293 kilograms) and was nearly nine feet long (2.7 meters).

As their name implies, Mekong giant catfish live in the Mekong River system in Southeast Asia. They’re the world’s largest scaleless freshwater fish and are called “royal fish” in the region because of their size and importance to local culture. (Learn about other giant fish.)

“This catch is exciting because it signals that the incredibly rare, endangered fish are still in the river and still making their annual spawning migration out of the Tonle Sap Lake and into the Mekong River,” Hogan says.

In the 1800s, thousands of Mekong giant catfish were caught in the river every year. But their numbers have declined by 95 percent due to overfishing, pollution, and habitat destruction. Now, less than half a dozen of the fish are spotted throughout their range in a year.

It’s illegal to kill the fish in the region, but the construction of a new series of massive dams on the river may choke off the catfish habitat.

“If all their spawning grounds are above the dams, they may be driven to extinction,” says Hogan, who has studied the fish for 20 years. “We just don’t know.”

To better understand the fish’s behavior, Hogan and officials from the Cambodian Department of Fisheries attached a plastic tag to the animal’s fin. If it is seen again, the team will have a better idea of its movements. The fish can live past 60 years old, so it could provide data for some time.

View Images The big fish was nearly seven feet long and weighed an estimated 200 to 250 pounds (90 to 114 kilograms). Photograph courtesy the University of Nevada, Reno

To release the behemoth, Hogan dove into the river about 10 feet (3 meters). It quickly swam off on its own and seemed to be in good health, he says. When it was first caught, fishermen had sprinkled it with perfumed water, a cultural sign of respect.

Check out Monster Fish on Nat Geo Wild or visit the new exhibit “Monster Fish: In Search of the Last River Giants” at the Terry Lee Wells Nevada Discovery Museum in Reno.