What Are the Differences Between Dolphins, Porpoises, and Fish?

No Relation

Fish is an animal classification along with mammals, birds, insects and reptiles.Jupiterimages/Photos.com/Getty Images

Fish breathe underwater by extracting oxygen as water passes through a system of gills. Whereas dolphins and porpoises have lungs, surfacing to breathe air through a blowhole. Most species of fish lay eggs, which usually are fertilized externally by the male's sperm. Some fish, like sharks, do give birth to live young. Baby fish survive on their own, while dolphins and porpoises care for their offspring. Dolphin and porpoise skin is smooth, with small hairs found around the blowhole or facial area; fish are normally covered in scales. Fish use a side-to-side motion to maneuver contrary to the up-and-down motion of dolphins and porpoises.

Although there are 33 species of dolphins, delphinidae, the most well known is probably the bottlenose, one of which portrayed "Flipper" on the television series. A rounded mound or melon on the head appears above a prominent snout or beak. Killer whales, false killer whales, pilot whales and melon-headed whales are all part of the dolphin family. Depending on the species, dolphins live up to 40 years, are very social and travel in groups called pods. The cone-shaped teeth come to a point. Dolphins produce sounds through echolocation to communicate and find food. The curved dorsal fin resembles that of a shark.

Unlike dolphins, porpoises are less social and difficult to see in the wild.Jupiterimages/Photos.com/Getty Images

With only six species, porpoises, phocoenidae, are elusive and shy of humans. Due to the short, blunt snout, the Greek translation of porpoise is "pig fish." They bear a triangular fin and have flat, spade-shaped teeth with sharp edges. The porpoise body is shorter and more compact, usually less than 7 feet in length. Harbour porpoises are the smallest cetaceans. Although they use the same type of sonar as dolphins to communicate and find prey, porpoise sounds are inaudible to humans. They live in smaller pods, up to 10, and live an average of 15 years.

Dolphin and porpoise females care for their calves up to two years until the young can survive on their own. Although adult dolphins and porpoises eat small schooling fish, squid and crustaceans, different habitats mean varied diets. For example, pacific white-sided dolphins consume salmon, anchovies, herring and squid, whereas the small Hector's dolphin, found off New Zealand's coast, eats red cod and yellow-eyed mullet. Many species make use of human fishing practices as they feed on escaped or discarded fish. Killer whales feed on fish and marine mammals such as seals, turtles and other species of dolphin.