Fish
Mekong Giant Catfish
Pangasianodon gigas · also called mekong giant catfish
The Mekong giant catfish is a river monster with a gentle diet. It grows to three metres and nearly 300 kilograms — among the largest freshwater fish on Earth — but as an adult it has no teeth at all and lives on algae and plant matter grazed from the riverbed. It is now one of the most endangered large animals in Asia.
Overview
The Mekong giant catfish lives in the Mekong River basin, historically from the Vietnamese delta upstream through Cambodia, Laos, and Thailand into southern China. It reaches about 3 m and 250–300 kg; a 293 kg fish caught in Thailand in 2005 is often called the largest freshwater fish on record.
A diet that changes with age
Young fish have teeth and long barbels and eat small animals. As the catfish matures it loses its teeth, its barbels shrink to stubs, and it switches to a purely plant-based diet — grazing and filtering algae and detritus, the same low-energy strategy that lets carp, manatees, and baleen whales grow large.
A migrant blocked by dams
The species migrates long distances up the Mekong to spawn. Large dams on the main river and its tributaries cut adults off from spawning grounds and larvae from nurseries, which is central to its collapse. In parts of the region the fish is sacred, and traditional catches were once preceded by ceremonies.
Status
The Mekong giant catfish is Critically Endangered, with the wild population estimated to have fallen by 80 percent or more over about three generations. Dams, overfishing, and habitat loss are the main threats. Fishing is banned across its range, and there are catch-and-release and captive-breeding programmes, but long-term survival is thought to depend on keeping stretches of the Mekong free-flowing.
Mekong Giant Catfish: common questions
How big does the Mekong giant catfish get?
It is one of the largest freshwater fish in the world. Confirmed large individuals reach around three metres in length and 250 to 300 kilograms in weight. The most frequently cited record is a female caught in the Mekong in northern Thailand in 2005 that weighed 293 kilograms, often described as the largest freshwater fish ever recorded, although a few other giant freshwater species, such as the giant freshwater stingray and the arapaima, are contenders depending on how size is measured. Fish approaching that size are now extremely rare.
How can such a huge fish live on plants?
The Mekong giant catfish is a grazer and filterer rather than a hunter. Adults have lost their teeth and have only tiny remnant barbels, and they feed by taking in algae, plant material, and organic detritus from the riverbed and the water. This is the same strategy that lets other very large animals, such as some carp, manatees, and baleen whales, reach great size on low-energy food — process a lot of it. Interestingly, young Mekong giant catfish do have teeth and longer barbels and eat small animals, then change over to the plant diet as they grow.
Why is the Mekong giant catfish Critically Endangered?
Three pressures acting together. First, dams. The fish must migrate long distances up the Mekong to spawn, and large dams on the main river and its major tributaries block these journeys and alter the flows, temperatures, and sediment that spawning depends on. Second, overfishing. The species has been caught for food and, in the past, for sport and record attempts, and because it is slow to mature, even modest catches outpace reproduction. Third, habitat loss and degradation from sand mining, pollution, and deforestation in the watershed. The combined effect has been a steep, sustained decline, and the fish is now protected across its range.
Can the Mekong giant catfish be saved?
Efforts are underway but the outlook is uncertain. Governments in the region have banned targeted fishing, and there are programmes to catch, breed, and release fish and to buy and free specimens taken accidentally. Captive breeding is well established because the fish grows fast in ponds. However, releasing hatchery fish does not address the core problem, which is that a migratory river fish cannot complete its life cycle if the river is cut into segments by dams. Long-term survival in the wild is thought to depend on maintaining free-flowing stretches of the Mekong and functioning fish passage, which is a much harder political and engineering challenge.