I've heard of people catching catfish on cut mackerel before. wasn't sure if anyone else had any experience with that.
Don't do it. Mackerel is considered a game fish in Texas, and you are not allowed to use it for bait. Some guys were fortunate enough to get just a warning from the game warden about that earlier this year. They got it at the Asian supermarket, so it didn't even cross their minds. Wouldn't have mine either.