The mola's odd shape disguises its true claim to fame: it's the heaviest bony fish in the world. Yes, yes, I know that whale sharks are really big, and they aren't whales, they're fish. But they're not bony fish — the skeletons of sharks and rays are made from cartilage. So when you look at all the other non-elasmobranch fishes out there, molas take the prize for size.