They look like the biggest fish in the world, but they are not fish. They have lungs and breathe air. They have large brains and live in family groups. They are cetaceans (si-TEY-shuns).
Cetaceans are not fish. They are mammals. That means they do not lay eggs. They have live babies and feed them milk. People are mammals, too, and so are dogs and cats.
Cetaceans are whales, dolphins, and porpoises. They swim in oceans all over the world. There are around 90 different kinds of cetaceans.
Whales are very big. The largest is the blue whale. It grows to be 100 feet long and weighs 200 tons!