There are about 60 species. Most inhabit tropical and temperate oceans, but there are some freshwater forms in rivers in Asia, Africa, and South America. The name 'dolphin' is generally applied to species having a beaklike snout and slender body, whereas the name 'porpoise' is reserved for the smaller species with a blunt snout and stocky body. Delphinus delphis is found in all temperate and tropical seas. The corners of its mouth are permanently upturned, giving the appearance of a smile, though dolphins cannot actually smile.
Dolphins feed on fish and squid.
There are five species of river dolphin, two South American and three Asian, all of which are endangered. The tucuxi Sotalia fluviatilis is not a true river dolphin, but lives in the Amazon and Orinoco rivers, as well as in coastal waters. As a result of living in muddy water, river dolphins' eyes have become very small. They rely on echolocation to navigate and find food. All dolphins power themselves by beating the tail up and down, and use the flippers to steer and stabilize.