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Fish are aquatic vertebrates that have gills for breathing underwater.
They are cold-blooded and found in bodies of fresh and saltwater around the Earth.
Most species of fish lay eggs which are fertilized outside the body, but some fish retain eggs inside the body and have live births.
Fish can be found in many different shapes and sizes. The smallest fish is only millimeters long, while some fish, such as the whale shark can reach a length of 65 feet!