Fishes are water-dwelling vertebrates with gills. Most are cold-blooded. There are over 29,000 species of fish, making them the most diverse group of vertebrates. Fish come in different sizes, from the 16 m (51 ft) whale shark to a 8 mm (just over ¼ of an inch) long stout infantfish. Other sea dwelling creatures, like dolphins, while closely resembling fish in outer appearance, are actually mammals.
