I'd have to agree, best pickled fish are shorthead red horse and the smallmouth buffalo is good too. I think the blue suckers would be tasty, but since there aren't a lot of them around, I'll have to pass.
Reason they're not as numerous as they once were has a lot to do with the lock and dam systems. Blues are like paddlefish and sturgeon and that they like to migrate long distances to spawn. Just can't do it when the locks are in the way. Their numbers increase dramatically as soon as you get south of the Keokuk lock and dam and their numbers are also slightly increasing in the interior large rivers as well. Not as bleak of a future as some of the other fish, but still needing some help.