One of the world's largest freshwater fish, an Asian catfish as big as a bear, may disappear in the near future, warns a UC Davis conservation biologist from his research base in Cambodia.

The giant catfish (Pangasianodon gigas), which grows to 10 feet long and 650 pounds, is a migratory species in the rivers of Thailand, Cambodia and Laos. It has been a mainstay for local fishers for centuries.

Now very few fish are being caught. At one typical traditional fishing spot on the Mekong River at Chiang Khong, Thailand, 30 fish were caught in 1995, seven in 1997, two in 1998 and none in 2000 and 2001.

Zeb Hogan is a conservation biologist and a UC Davis doctoral student studying the fish on the Mekong and Tonle Sap rivers. "I'd go down to where the fishermen had their nets out and ask, 'Caught any fish?' And they never did," Hogan said.

"Here is a fish that has been caught for hundreds of years. Now it looks like it's on the way out."

Hogan's doctoral adviser is UC Davis fisheries biologist Peter Moyle. Like some of the California native fish that Moyle studies, the giant catfish migrate hundreds of miles each year between downstream feeding areas and upstream spawning areas.

"The giant catfish and other fish in this diverse ecosystem are extremely important to the health and economic well-being of local peoples but are threatened by the construction of hydropower dams and other problems," Moyle said. "We hope that Zeb's work will help call attention to a potential impending ecological and social disaster."

Hogan's research is funded by the Cambodian Department of Fisheries, the conservation group Save Cambodia's Wildlife and the National Geographic Society's Conservation Trust.