The Imperiled giants of the Mekong river.

Ecologists struggle to understand-and protect-Southeast Asia’s large migratory catfish. The Guinness Book of World Records lists the Mekong giant catfish as Earth’s largest freshwater fish.
This species (Pangasianodon gigas), which grows as fast as a bull and looks a bit like a refrigerator, can measure 3 meters in length and weigh up to 300 kilograms.

Called the “king of fish” in Cambodia, “buffalo fish” in Thailand and Laos, and “blubber fish” in Vietnam, this catfish is well known throughout Southeast Asia. Only the caviar-producing sturgeon, goliath catfish of the Amazon and a few species of poorly understood freshwater sting rays rival the Mekong giant catfish in size. In Europe, the Wels catfish (Silurus glanis) reportedly once grew to a monstrous 5 meters in length, but today a 2-meter specimen is considered remarkable.

A century ago, the range of the Mekong giant catfish spanned the entire length of the river and its tributaries from Vietnam to southern China. But in the 1930s and ’40s, this species began disappearing, first from the segment of the Mekong that flows between Thailand and Laos and later upstream, in northern Laos. During recent times, the status of P. gigas has become extremely precarious. For example, in Chiang Khong (northern Thailand) and across the river in the Houay Xai district (Laos), the 1990 haul included just 69 of these fish. The catch from this stretch of river has fallen considerably since then, and over the past three years local fishers have not reported a single one. Noting this absence and similar patterns unfolding elsewhere, we estimate that the total number of these giant catfish has decreased by 90 percent or so during the past two decades.

Efforts to save this fish from extinction will hinge on many factors–including how well biologists understand the migratory behavior of these animals. Using a variety of approaches, we have endeavored to provide such knowledge. Here we relate how we became involved in this effort and where that journey of discovery has taken us. zz