"What makes a fish a fish? Trout thinks he knows the answer. "That's easy! Fish have fins, gills, scales, are shaped like me, and live underwater." "Not so fast," answers Mudskipper. "What about a clingfish? They don't have any scales. Or a hagfish? They don't have any fins. Or what about me? I live in and out of the water!" As Trout and Mudskipper explore below and above the world's waters, they are introduced to a multitude of fish in various shapes,...