There's always a vast difference of opinions among anglers when it comes to choosing baits. Most think that catfish bait have to be "stinky" or they default to chicken livers.
When it comes to blue catfish there's no bait that's better than cut bait and gizzard or threadfin shad usually top the list of fish to use for cut bait.
This is an infographic I put together that covers all the basics on locating and catching shad for catfish bait and some of the information needed for using it for catfish bait. It's a summary of a much longer article that goes into more detail on using shad for catfish bait.