Juvenile Mekong giant catfish have barbels and teeth and take small prey. As they mature both largely disappear. The adult mouth is a broad, blunt scoop suited to rasping algae and detritus from submerged surfaces, and gut contents from captured fish are dominated by plant material.
The size record is well documented: a fish of about 293 kilograms and roughly 2.7 metres was landed in northern Thailand in 2005, one of the heaviest freshwater fish ever weighed. Growth is fast in the first years, which is part of how a herbivorous diet supports that mass in a warm, productive river.
The species is Critically Endangered. Mainstem dams, which block the long upstream migrations to spawning reaches, and heavy fishing pressure have driven a steep decline. Where exactly the remaining fish spawn is still not confidently mapped, which makes protecting the right river reaches difficult.