They don't look like each other and are not even in the same taxonomic group. But they share the same name and cause plenty of confusion. The dolphinfish is a golden-colored creature with sporadic hues of blues, greens, white and yellow. It's much smaller than the typical dolphin mammal, and has a blunt, flat forehead in contrast with the dolphin's beaked face. While dolphins are protected from capture under the Marine Mammal Protection Act, dolphinfish are heavily fished and marketed under the name "mahi mahi." To save a syllable and add to the confusion, many refer to the dolphinfish as a "dolphin."
The name "mahi mahi" comes from the Polynesian language and literally means, "strong strong." Two species of dolphinfish may be marketed as mahi mahi: common dolphinfish and pompano dolphin. Retailers and restaurants might also sell mahi mahi under the name "dorado," which means "golden" in Spanish and underscores the fish's characteristic golden color. While restaurants may have formerly used the terms "dolphin" or "dolphinfish" on their menus, many switched to "mahi mahi" to avoid confusion and outrage among guests.
Apparently few answers exist about how and why the term "dolphin" became attached to the mahi mahi fish. In fact, the etymology of the word "dolphin" reveals that the term originally meant "womb." So the word fits the dolphin, the marine mammal, since female dolphins give birth to live young -- they have wombs. Dolphinfish, though, are fish; they don't have wombs and they don't look like dolphins. The writing staff at BlueWater magazine had similar questions about the dolphinfish's strange name and formed one theory. Underwater, the dolphin and dolphinfish make similar high-pitched noises to communicate. So the dolphinfish may get its name because of this dolphin-like trait.
Since the dolphinfish swims in a category starkly different than the dolphin and because of the fish's high reproductive rates, you don't have to fear selecting the dolpinfish from a restaurant menu or from the store. According to organization Seafood for the Future, the New England Aquarium lists dolphinfish as an "ocean friendly seafood choice." It's also a fish that's fairly easy to catch and is favored among fishers. Perhaps even better, the International Game Fish Association cites the dolphinfish -- mahi mahi -- as delicious food.