* Warm-blooded: Whales maintain a constant internal body temperature, unlike fish which are cold-blooded.
* Breathe air: Whales have lungs and must surface to breathe air, unlike fish which breathe through gills.
* Give birth to live young: Whales give birth to live young, which are nourished with milk produced by the mother. Fish lay eggs.
* Have hair (at least during some stage of life): While some whales have very little visible hair, they do have hair follicles.
* Streamlined bodies: Both whales and fish have streamlined bodies, which is an example of convergent evolution (developing similar features due to similar environments).
Although they live in the ocean, whales are more closely related to land mammals like cows, horses, and humans than they are to fish.