Catfish are the largest, scaleless, freshwater fish in the world. They are found in freshwater environments of all kinds, with species on every continent except Antarctica. All catfish, except the electric catfish, have the ability to deliver a stinging protein which can be extremely severe to humans.

The largest catfish is the Giant Mekong Catfish in Southeast Asia. They can grow to 3 m long and weigh up to 300 kg. However, it is in danger of disappearing from Thailand completely. There have not been any giant catfish captured in Thailand since 2001. Threats to the giant catfish include commercial fishing and dynamite blasting of their spawning ground. The catfish is also sold to tourists, who are told that the fish imparts wisdom if eaten.