Toggle Nav

River of Giants: Giant fish of the Mekong

Watch WWF’s Dekila Chungyalpa (at minute 110:06) as she testifies in front of the Senate Committee on Foreign Relations on “Challenges to Water and Security in Southeast Asia.”
Read the written testimony

WWF’s new River of Giants: giant fish of the Mekong report profiles four giant fish living in the Mekong that rank within the top 10 largest freshwater fish on the planet. This report highlights the dangers associated with hydropower development on the mainstream of the lower Mekong River basin.

Read the press release about the report

WWF’s River of Giants reportAny impact on the ecological balance of the river also threatens the sustainability of the aquatic resources that support millions of people. There are at least 50 migratory species which are highly vulnerable to mainstream dam development. These make up between 40-70 percent of the catch of fish in the Mekong.

“Lower Mekong River mainstream” refers to the mainstream of the Mekong River beginning just below the Chinese border. The river from this point travels through Cambodia, Laos, Thailand and Vietnam before it empties into the South China Sea. Today, this section is free-flowing and unimpeded by dams.

There are 11 hydropower dams planned for the lower mainstream of Mekong River mainstream. The Sayabouly dam, located in northern Laos, is the first lower Mekong River mainstream dam to enter a critical stage of assessment before member countries of the Mekong River Commission advise on whether to approve its construction.  The proposed dam is a threat to the survival of the Mekong giant catfish, and could contribute to the escalation of climate change impacts to the Mekong River Delta. Click to view a map of the region.

Mekong Giant Catfish: driven to extinction?

Ranked as the third largest fish in the world, perhaps the most famous catfish in all of Asia is the gigantic Mekong giant catfish. In 2005, a colossal 9-foot (2.7m), 645-pound (293kg), car-sized specimen was caught in northern Thailand and was recorded as the largest freshwater catch.

Many scientists and local fishermen consider the section of the Mekong River between Chang Rai, Thailand, and Bokeo, Laos, a critical area for spawning. This area is one of the last places in the world where the critically endangered Mekong giant catfish is believed to be spawning in the wild. As the catfish is a long-distance migrant between the Tonle Sap Lake in Cambodia and the Mekong River in northern Thailand and Laos, any dam built on the mainstream of the lower Mekong River will prevent the species from migrating to its spawning grounds. This will mean that the species cannot increase its numbers and its population will plummet to unrecoverable levels.

Worse impacts of climate change?

The Mekong River Delta is one of the three most threatened deltas in the world from the impacts of climate change. Building the Sayabouly dam would reduce sediment and nutrients from flowing downstream to the Mekong River Delta. This will reduce the ability of the delta to replenish itself and lead to increased coastal erosion and greater vulnerability to climate change impacts such as inundation and saltwater intrusion from sea level rise. This will potentially displace millions of people and cause the loss of agricultural land worth millions of dollars.

Species spotlight: Dog-eating catfish

Scientific name: Pangasius sanitwongsei

Also known as: Paroon shark; ChaoPhraya giant catfish

Date of discovery: Smith, 1931

Maximum size: 660 lbs. (300kg), 10 feet (3m)

Defining features: Very elongated dorsal fin

Distribution in the Greater Mekong: Cambodia, Laos, Thailand, Vietnam and Yunnan Province (China). Endemic to the Greater Mekong

Diet: Carnivore

Average lifespan in the wild: Unknown, but can reach 20 years in captivity

Threats: Overharvesting for local and commercial fisheries, habitat loss, pollution and aquarium trade

Experience the Mekong River

See close-up footage of the Mekong Giant Catfish.

Join a WWF scientist as he takes samples from the Mekong River.

What WWF is doing

The 1995 agreement of the Mekong River Commission should be fully recognized and endorsed; in particular the procedures for notification, prior consultation and agreement. WWF supports a delay in the approval of the mainstream dams, including the Sayabouly hydropower dam in Sayabouly Province, Laos, to ensure a comprehensive study is undertaken to fully understand all the positive and negative impacts of their construction and operation. WWF encourages others to join in supporting the Mekong countries to commit to the study phase.

To meet the region’s urgent energy demands, WWF promotes sustainable hydropower projects on selected tributaries of the Mekong River, prioritising those that already have hydropower dams developed on them. WWF is developing tools to help assess which are the best tributaries in the lower Mekong River basin to develop hydropower on, and which ones should be kept free flowing if the ecological integrity of the whole Mekong river system is to be maintained.

Learn more about our work in the Mekong

Connect with WWF