Here are some differences between fish and marine mammals.
| Fish | Marine Mammals |
| Fish swim by moving their tail from side to side. | Marine mammals swim by moving their tail up and down. |
| Fish have gills so they can breathe underwater. | Marine mammals do not have gills. They have to come to the surface to breathe. |
| Fish are cold-blooded animals. |
Marine mammals are warm-blooded. |
Whales in the sea