Ditto on what Bill said about fish being adaptable and occupying overlapping niches. Think catfish and suckers are bottom feeders? Not necessarily. Back when I was a biologist aide Intern for a summer we routinely gillnetted channel catfish that were far up off the bottom suspended in a reservoir. I know of a natural lake near me where suckers are routinely gillneted suspended far off shore too. Here's the kicker. The suckers were feeding on plankton even though they had downturned mouths!

If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.