Caught last month (May 1) in the Mekong River, a team of fishermen struggled for more than an hour to haul the creature in. It tipped the scales at 646 pounds (293 kilograms).
Despite efforts to keep the Mekong giant catfish alive, it died and was later eaten by villagers.
The Mekong giant catfish (Pangasianodon gigas) species is listed as critically endangered by the World Conservation Union (IUCN), which means it faces a high risk of extinction in the wild. The rare specimen, captured in Chiang Khong district, is the largest since Thailand began keeping records in 1981.
The giant catfish is currently the focus of a World Wildlife Fund and National Geographic Society project to identify and study the planet's biggest freshwater fish—those that grow to 220 pounds (100 kilograms) in weight or more than 6.5 feet (two meters) in length.
"It's amazing to think that giants like this still swim in some of the world's rivers," said project leader Zeb Hogan, a National Geographic Society emerging explorer and a WWF conservation science fellow.
"We believe this catfish is the current record-holder—an astonishing find," Hogan added. "I have heard of three-meter-plus [ten-foot] catfish in Bulgaria, 500-kilogram [1,100-kilogram] stingrays in Southeast Asia, and five-meter [16-foot] arapaima in the Amazon, but up until now we have not been able to confirm these reports."
Other contenders for the title of world's largest freshwater fish include the Chinese paddlefish and dog-eating catfish—another Mekong giant.
Hogan says such big species are poorly studied and in urgent need of protection. "In many locations they are now so rare that the opportunity for documentation and study may soon be lost," he said.
Photographer Suthep Kritsanavarin witnessed the record catch on the Thai side of the Mekong, across the water from Laos. "I may never see anything like it again in my lifetime," he said.
Kritsanavarin says only four other Mekong giant catfish were landed this year.
Thai fisheries officials had hoped to release the adult female after stripping it of eggs for a captive-breeding program. Unfortunately, the fish didn't survive its ordeal.
Mekong giant catfish are caught in Chiang Khong district in April and May when they run upstream to their spawning grounds.
Fishermen hold an annual ceremony at the start of the fishing season when they ask a river god for permission to catch the fish. "Chicken sacrifices are performed aboard the fishing boats," Kritsanavarin said.
There's long tradition of giant catfish fishing in Thailand and Laos. Hogan says cave paintings of the fish in northeast Thailand show it has captured the imagination of people living along the Mekong for more than a thousand years.
"Mekong people believe it's a sacred fish because it persists on plant matter and 'meditates' [in the deep, stony pools of the Mekong River]—somewhat like a Buddhist monk," Hogan said.
The fish attracts high prices in Thailand, because eating it is supposed to bring good luck. Chinese believe the meat boosts intelligence and prolongs life.
"From what I've heard, the fish has a slightly muddy taste," Hogan added. "Cambodians, who don't believe eating the fish brings good luck, say it's not a good-tasting fish and sell it at a low price."
Conservationists are deeply concerned for the fish's future. Hogan says historic catches suggest the population was once between a hundred and a thousand times larger than it is today.
Reasons for the collapse in numbers are unclear, though likely factors include over-fishing, degraded habitats, and the construction of dams, which block the fish's movements. Mekong giant catfish spawn in the Golden Triangle—a region where the borders of Thailand, Laos, Myanmar, and China meet.
WWF's Rob Shore works on the Living Mekong Programme, based in Phnom Penh, Cambodia. He says governments of lower Mekong countries have introduced measures designed to protect the species.
Tagging and Release
In Cambodia, a tagging and release program operates for several big Mekong fish species that are caught in nets stationed in the main river channels. These species include the giant barb (a type of carp), the giant freshwater stingray, and the river catfish.
The fish are tagged, measured, and then released. Fishermen are compensated for the return of these fish to the wild. Zeb Hogan has been running this project.
"The reporting network actually works quite well, partly because of the revered status of Mekong giant catfish," Shore added.
In northern Thailand, giant catfish fishing is allowed for research and conservation purposes. Milt and eggs are taken for a reintroduction scheme run by the Thai government. In 2001 the first offspring were raised from captive-bred parents. It's still unclear whether these artificially reared young succeed in the wild.
Shore says the conservation of the Mekong giant catfish is also vital for a host of other migratory fish species that rely on the same environments. "In turn, these species sustain the lives and livelihoods of millions of people," he said.
Zeb Hogan says a species-conservation action plan for the whole Mekong Basin is an urgent priority as there is no cross-border strategy to protect the fish. An action plan is currently being prepared by the IUCN's Mekong Wetlands Biodiversity Programme.
Other priorities include sustainable fishing methods, improvement of critical habitat, identification of spawning sites, and the creation of protected freshwater areas.
Hogan hopes to raise the profile of other seriously threatened big freshwater fish species around the world. The WWF-NGS great fishes project will travel next to China and Australia before heading for Africa, South America, and the United States.
"The challenge is clear—we must find methods to protect these species and their habitats," Hogan added. "By acting now, we can save animals like the Mekong giant catfish from extinction."
It was initially reported incorrectly that the giant catfish caught in Thailand was male.