The largest freshwater fish currently alive is the endangered Mekong Giant Catfish Pangasianodon gigas (there are sturgeons which are much heavier and longer, however they are classified as anadromous—they breed in freshwater but live in the sea). The largest Mekong catfish on record have measured up to 3.2 meters (10 feet) with a mass greater than 300 kilograms (660 pounds). Ichthyologists know little about the life patterns and spawning habits of the enigmatic Mekong catfish. Juvenile catfish undergo an omnivorous stage when they eat insect larvae, zooplankton, and other small fish (including smaller juvenile Mekong catfish). As soon as they reach their adult stage the catfish lose their barbels (the “whiskers” from which catfish derive their common English name) as well as their teeth to adapt a vegetarian diet of algae. The adult fish are silver or gray with yellowish bellies.
Giant catfish once lived throughout South East Asia in the waterways of Laos, Cambodia, Thailand, Vietnam, Myanmar and Yunnan. But today, overfishing, dam-building and industrialization have taken a heavy toll: the Mekong Giant Catfish can only be found in Mekong River and its tributaries in Cambodia, Laos and Thailand.
Because of their giant size and their mysterious habits, the catfish have a place in the mythology and folklore of South East Asia. The fish feature in many tales of Buddhist monks, najas, and water spirits. Miranda Leitsinger, who wrote an article about the fish, even relates a story of ritual human sacrifice, “In Laos, legend has it that four centuries ago, the king used to sacrifice a man and woman each year to cave spirits to get their permission to catch the giant catfish.” Apparently the cave and water spirits are not the force they once were, because today the Mekong giant catfish is rapidly becoming a legend itself.