A fish is an animal that has to spend all its time in the water. If it comes out of the water for too long of a time, it will die. A fish uses gills to get oxygen (air to breathe) from the water. Fish are usually covered with scales. One kind of fish is the shark. Some people keep fish as pets, and some people like to eat fish.
Some fish live in fresh water (or sweet water), and some fish live in salt water. It is also possible for fish to live in water where a river runs into an ocean and the water mixes. This is called brackish water.
People eat many kinds of fish. The fish that people eat most include carp, cod, herring, perch, sardines, tilapia, trout, tuna, and many others. Some people keep fish as pets. Goldfish are a popular type of pet fish.
Most kinds of fish have bones. Some kinds of fish, such as sharks and rays, do not have real bones (their skeletons are made of cartilage). Some scientists say that these are not real fish, but most people call them fish. Some other animals that live in the sea, such as starfish and jellyfish, are called fish, but are not really fish.
The word to fish is also used for the activity of catching fish. People catch fish with small nets from the side of the water or from small boats, or with big nets from big boats. People can also catch fish with fishing poles and fishhooks with bait. This is often called fishing.
Some of this page comes from the Wikipedia article on Fish