This document provides information on the history and anatomy of fish. It begins with the earliest fish, the ostracoderms from the Ordovician Period, and discusses the evolution of jaws in placoderms and acanthodians. It then describes the general characteristics of modern fish, including their external anatomy such as fins, scales, skin and internal organs. The document also covers fish feeding, reproduction as egg-layers and scatterers, and care of marine invertebrates.