The Mekong giant catfish is called the "king" of the Mekong River due to its sheer size. It can grow up to three metres in length and weigh as much as 350 kilograms.

Its numbers have, however, been steadily falling for decades. At Ban Hat Khrai in Chiang Rai's Chiang Khong district - the major fishing grounds for the species - fishermen said they couldn't even land one giant catfish in 2001 and 2003. The record catch is 69 fish in one season, but that was made many years ago.

The World Conservation Union has put the Mekong giant catfish on its red list of critically endangered species.

Scientists know preciously little about the fish, except that it is mild-mannered and easily spooked. The catfish migrate upstream and there at least 10 places where they can be sighted, including China's Dali passage and Cambodia's Tonle Sap, Southeast Asia's largest freshwater lake. Chiang Rai is the only big fishing spot. As giant-catfish fillets are prized by wild-game connoisseurs, a local tourism promotion campaign in Chiang Khong began promoting the fish.