Honeyboy Edwards says it was made by Robert Petway:

"'Catfish Blues' is Robert Petway's song. He just made that song up and used to play it at them old country dances. He just made it up and kept it in his head. You call that mother wit. He remembered every verse he ever sang; didn't have towrite down nothing. I learned the 'Catfish' from Robert. Robert and Tommy McClennan and me, we'd be together all the time." (David Honeyboy Edwards, The World Don't Owe Me Nothing: The Life and Times of Delta Bluesman Honeyboy Edwards, Chicago Review Press, 1997, p. 32)

~Masato