In tropical seas, flying fish leap out of the water, gliding for up to 200 meters, before dipping back into the sea. In the Indo-Pacific, a hunting sailfish swims up to 110 kilometers per hour. These feats are made possible by a fish’s form — which in most species is a smooth, long body, fins, and a tail. Lauren Sallan explains why these features are so common, and what it reveals about fish.