>It's also worth noting that fish in particular may be so widely varied because they're miscategorized; there's a push among some biologists to split up "fish" into several differently groups because there's so much more variation among "fish" than among equivalent groups.

While this is true, the splits would be jawless fish, sharks and rays, lungfish and kin, and everything else. So a huge chunk of the diversity of fish, and especially the colorful fish, is actually in one group of fish.