Unlike most catfish, the Mekong giant catfish is a pure vegetarian. It eats only algae (the green slippery stuff that grows on rocks underwater) and plant material. Despite its enormous size, it has no teeth - just a wide, smooth mouth designed for grazing on surfaces.
The catfish can live for up to 60 years. It starts life as a tiny transparent egg in the upper Mekong, then grows slowly over decades into the giant it becomes. Young catfish swim in small groups; older ones are often found alone in the deep, slow parts of the river.
Scientists first recorded its enormous size properly in 2005, when a fisherman caught one weighing 293 kilograms - the largest freshwater fish ever properly documented. The fish was later released back into the river as part of a study.
The Mekong giant catfish is critically endangered, which means it is in real danger of disappearing. Conservation projects in Laos, Cambodia and Thailand are working to understand the fish better and protect the deep river areas where it lives and breeds.