June 29, 2005-A fish to validate even the tallest fishing whopper was wrestled out of a river in northern Thailand a month ago. The 646-pound (293-kilogram) Mekong giant catfish measured nearly nine feet (2.7 meters) long-thought to be the largest freshwater fish on record.

Scientist Zeb Hogan, who is on a National Geographic-sponsored expedition to study the great freshwater fishes of the world, said he scoured Thai and other records but could not find any fish that weighed more than this one. "If there are reliable records of larger freshwater fish, I'd like to know about them," he said.

The Thai fishers who caught the giant catfish struggled for more than an hour to land the behemoth. At first it was hoped the male fish could be returned to the river to continue its spawning migration. But the fish died and ended up feeding almost an entire village. (View a photo of villagers butchering the fish.)

"I'm convinced that there are even larger living freshwater fish, even catfish," Hogan said. "I think the giant freshwater stingray is probably the biggest of the freshwater fishes. I've heard stories that they can weigh 500 kilograms [1,100 pounds] or more, and I believe them." (View a photo of a giant freshwater stingray.)

The giant catfish caught in Thailand needs to be put in context, Hogan said. "These giant fish are uniformly poorly studied and some are critically endangered. Some, like the Mekong giant catfish, face extinction. My study of giant freshwater fish is showing a clear and global pattern: the largest fish species are disappearing. The challenge is clear-we must find methods to protect these species and their habitats."

-David Braun