Why do fish have such varied body shapes?

The variety of fish is very large. Along with this, the shape of the body of fish is very diverse. Almost all fish have a well streamlined body shape. But changes did occur in the course of evolution. Some fish need to swim quickly as they are predators or may become prey themselves. Some fish do not fall prey due to special adaptations, so they do not need to swim fast. Also, the shape of the body may change due to the depth of the fish habitat, since the pressure is different in different layers of water.