Fish are aquatic animals that are found in a variety of different habitats, including oceans, rivers, lakes, and ponds. They come in all shapes and sizes, with over 33,000 known species of fish worldwide. Fish have played an important role in human history and continue to be an important source of food and recreation for many people around the world.

Fish are cold-blooded animals, which means that their body temperature is regulated by the temperature of the surrounding water. They have gills that allow them to extract oxygen from the water and a streamlined body that helps them move through the water with ease. Many fish also have scales that protect their bodies and fins that help them swim.

Fish are divided into two main categories: bony fish and cartilaginous fish. Bony fish, which include most of the fish that we eat, have skeletons made of bone. Cartilaginous fish, such as sharks and rays, have skeletons made of cartilage.