Although they live in different environments, both whales and guppies are vertebrates that have lungs and breathe oxygen from the air. Whales are mammals that live in the ocean, while guppies are fish that live in freshwater. Whales have blowholes on the top of their heads that they use to breathe air, while guppies have gills that they use to extract oxygen from the water. However, both whales and guppies must regularly come to the surface of the water to breathe air.