Tsk, tsk-- it's in the FAQ (isn't everything?):

Define "mudcat"

mud cat

any of several catfishes capable of living in Muddy Waters.

Source: Webster's New World College Dictionary

Catfish and Muddy Waters are inextricably connected to the Blues. Max started the place as a blues site, but generously invited us folkies to join him. Sometimes, he's still not too sure of us. Ask him what he thinks of Gordon Bok.

~S~