They'll eat pellets or algae pellets. They are good for cleaning up uneaten food that the top-swimming fish missed. They are passive and will mix with most medium/low aggression fish. There is also an albino variety, pictured below all of the 'normal' bronze catfish.
The big one on the right here is a peppered catfish.
Here is a photo of the albino variety, commonly known as albino cory catfish, or something similar.