From Encyc

Catfish is a type of bottom-dwelling freshwater fish that is popular in the United States, particularly in the South. They are an economically important aquaculture species, and efforts have been made to market them in the North and even as far as Europe, where the locals eat carp, which is basically just a big goldfish.

Fishing for catfish can be done any number of ways but some individuals like to find where they hide and then get the catfish to bite their thumbs, and then they are able to pull them out of the water that way.