—Photograph courtesy Zeb Hogan/WWF Conservation Science Fellow/National Geographic Emerging Explorer
Read Caption

The critically endangered Mekong giant catfish, such as this one on a fisherman's boat, is one of the largest freshwater fish in the world.

—Photograph courtesy Zeb Hogan/WWF Conservation Science Fellow/National Geographic Emerging Explorer

Mekong giant catfish

The Mekong giant catfish is the official freshwater heavyweight champion of the world. According to the Guinness Book of Records, a nine-foot-long individual caught in northern Thailand in 2005 weighted an astounding 646 pounds, making it the largest exclusively freshwater fish ever recorded.

Despite its gargantuan size, but also because of it, the giant catfish lives a tenuous existence in the murky waters of its native river, Southeast Asia’s Mekong, where its numbers have plummeted so dramatically that the species is on the brink of extinction.

Appearance, diet, and behavior

Gray to white in color and lacking stripes, the Mekong giant catfish has very low-set eyes, which gives it a slightly sorrowful appearance. They are distinguished from other large catfish species by their near-total lack of barbels, or “whiskers,” as well as by the absence of teeth. (Juveniles have barbels, but these features shrink as they age.)

As babies, they feed on zooplankton in the river and are known to be cannibalistic. After about a year, they become herbivores, and eat plants and algae.

The Mekong giant catfish has one of the fastest growth rates of any fish in the world. It can reach up to 440 pounds in only six years. They can live up to 60 years.

Highly migratory, the species requires large stretches of river and very specific environmental conditions for its seasonal journey to spawn and breed. While scientists don’t know exactly how the fish move, the Mekong giant catfish is believed to spend much of its time feeding in Cambodia’s Tonle Sap Lake and then migrating hundreds of miles north to spawning grounds in Thailand.


These giant catfish were once plentiful throughout the Mekong basin, but their numbers are believed to have dropped by at least 95 percent over the past century. With no population figures available, estimates of the decline are based on the fall in the number of fish caught. Some experts think there may be only a few hundred, or even fewer, adults left in the Mekong River.

Overfishing is the primary cause of the giant catfish’s decline, but damming of Mekong tributaries, destruction of spawning and breeding grounds, and siltation (a process by which water becomes dirty with fine mineral particles) have also taken a huge toll.

Conservation efforts

Conservationists have focused on the Mekong giant catfish as a flagship species to promote conservation on the river. It is now illegal in Thailand, Laos, and Cambodia to harvest the critically endangered species, though giant catfishes still are illicitly caught, with some sold to restaurants in Vietnam.

In Thailand, Mekong giant catfishes have been successfully bred in artificial ponds, but efforts to introduce these fish in the wild have largely failed.

440-pound giant catfish saved

Watch as a Thai community rescues a 440-pound Mekong giant catfish displaced by flooding in 2017.