Many animals live in water, but only some can be defined as fish. Twenty-eight thousand species of fish exist, each with different characteristics. Readers from grades one through four will learn that fish have a distinct impact on their ecosystem and will see how fish survive when well-adapted to an uncompromised environment. Beautiful photographs demonstrate the great diversity of fish and accompany intellectually stimulating explanations of their varying roles and traits. From page to page, what a fish is unfolds in vocabulary call-outs, insightful questions, and relatable compare-and-contrast examples.