Dolphins spend their entire lives in the ocean, yet they are mammals, not fish. Everything about how they breathe, reproduce and feed their young puts them with the mammals, not with the fish.
An Eastern Spinner Dolphin, recognizable by its triangular dorsal fin and uniform gray color. Credit: NOAA.
Mammal or fish?
| Dolphins | Fish | |
|---|---|---|
| Body temperature | warm-blooded, like every mammal | — |
| Breathing | air, with lungs | water, with gills |
| Young | born alive | hatched from eggs |
| Feeding the young | milk | — |
| Body covering | a tiny amount of hair, around the blowhole | scales |
A nose on top of the head
Because they breathe air, dolphins must come to the surface often to catch a breath. The blowhole on top of the head works as a "nose," which makes it easy for a dolphin to breathe as soon as it surfaces.
Not the only sea mammals
Whales and porpoises are mammals too. There are 75 species of dolphins, whales and porpoises living in the ocean, and along with manatees they are the only mammals that spend their entire lives in the water.
Sources
Based on "Are dolphins fish?" from NOAA's National Ocean Service, a work of the United States government in the public domain.
Licence: CC0 1.0 (public domain) · Adapted from oceanservice.noaa.gov
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