Name five animals that belong to the fish group.

Fish are the first vertebrates that evolved on Earth. A vertebrate is an animal that has a backbone. Fish include animals with backbones that are adapted to live in water using specialized gills to breathe.

Gills are filamentous and contain many capillaries. This provides a thin, moist environment for gas exchange--oxygen in and carbon dioxide out. Water enters the mouth of the fish and is then pumped over its gills where gas exchange occurs. Then,...

Fish are the first vertebrates that evolved on Earth. A vertebrate is an animal that has a backbone. Fish include animals with backbones that are adapted to live in water using specialized gills to breathe.

Gills are filamentous and contain many capillaries. This provides a thin, moist environment for gas exchange--oxygen in and carbon dioxide out. Water enters the mouth of the fish and is then pumped over its gills where gas exchange occurs. Then, the water exits through openings on the sides of its pharynx.

Most fish have paired fins to help stabilize their movements as they swim. Fish are ectothermic and their bodies are covered by scales. 

Jaws, another adaptation that evolved in fish provide the opportunity to feed on many different types of foods. Some fish are herbivores and eat algae, some are carnivores and are predators of other organisms, some eat detritus and others can be parasitic.

Fish have a closed circulatory system with a single loop for the blood to follow in a pathway that is pumped by the heart. Fish can remove the nitrogenous waste ammonia by the action of kidneys. Fish have a well-developed brain and nervous system that can process smell, sight, sound, touch and vibrations. 

Fish reproduce sexually. Some have external fertilization and development and some species can have their eggs fertilized internally and develop internally where the embryos feed on a yolk sac. Still others have internal fertilization and the young receive nourishment from the mother's body. 

One of the two main groups of fish are cartilaginous fish including sharks, skates and rays. They contain a skeleton made from cartilage and have tooth-like scales on their skin. The other main group is the bony fish which  have skeletons consisting of bone. Most have fins that are spiny and thin and are called ray-- finned fish.  Some examples include salmon, trout, bluefish, seahorse and tuna.

These are just a few examples of the variety of fish that exist in freshwater or salt water habitats.