By Holly Lynn Anderson
Clearing up the confusion between a dolphin and a dolphinfish illustrates two common problems when discussing inhabitants of the aquatic kingdom: swimming in the ocean doesn’t necessarily make you a fish; and the same species can have many different common names.
Common names can be different in different countries or even in different regions of the same country. It is also not unusual for very different species to have similar common names. One of the best examples is the difference between a dolphinfish and a dolphin.
Dolphins are mammals and breathe air with lungs just like humans. There are many different dolphins species, including endangered river species, but all of them are in the same animal family (Delphinidae). Like humans, dolphins must come to the ocean surface to ingest a breath of air in one of two ways: through their mouth or via an alternate air source that allows them to breathe while keeping their mouth in the water. Human swimmers can breathe just as easily through nostrils as their mouth. Likewise, a dolphin can breathe through its blowhole.
As a mammal, dolphins also have other characteristics in common with humans: both give birth to live young, who feed on milk from their mother’s body; both are warm-blooded and both have hair. (Dolphins have fine hairs around the blowhole.) There are more than 75 species of dolphins, whales, porpoises and manatees in the world, all of which are the only mammals that spend their entire lives in the water. So, even though they swim in the ocean, dolphins are not fish.
Dolphinfish are very different. Technically, there are two species of dolphinfish that are so similar that the both are referred to by their more popular common name mahi-mahi. The common dolphinfish (Coryphaena hippurus) and pompano dolphin (Coryphaena equiselis) can be difficult for non-experts to differentiate, with the primary difference being that pompano dolphin are smaller in depth and length and the larger dolphinfish. Adding to the confusion, both species tend to live in the same habitats meaning that where you find one, you will likely also find its closest relative.
The larger of the two dolphinfish, the common dolphinfish, can grow to up to 6 feet in length and weight between 80 to 90 pounds. Dolphinfish are bright in color, often displaying brilliant greens and blue colorations. They also are known for their blunt, flat head.
The dolphin, on the other hand, varies in length and weight, depending on the specific species, but usually grow longer than 10 feet and weight more than 1,000 pounds. With a long rostrum (snout), the head of a dolphin is angular and pointed, compared to the flat head of a dolphinfish. Dolphins are also grey and white in coloration as opposed to brightly-colored, smaller dolphinfish.
Aside from their confusing name, there is no connection between the dolphin and the dolphinfish. In fact, dolphins, as air-gulping mammals, have more in common with humans then dolphinfish, which use gills to filter oxygen from water. The confusion between the two is exclusively in their similar names.
The Hawaiian name for dolphinfish—mahi-mahi—means strong. The mahi-mahi is difficult to reel in when caught, making it a favorite of sport fishermen. It is also a tasty fish and is usually identified as mahi mahi (no hyphen) on restaurant menus in the United States. In Mexico, it is called dorado from the Spanish word for gold.
If you see mahi-mahi or mahi mahi or dorado on your next menu, you don’t need to worry that you’re eating Flipper. The meal served in restaurants is a fish, not a mammal.
To further ease your concerns the next time you go to a restaurant, the fast growth rate of dolphinfish means it is not an endangered species despite being popular with both sport and commercial fishermen. In just three months, the dolphinfish can “grow from nearly microscopic larvae to a foot and a half” in length and weigh several pounds.
The term mahi mahi is being used more often than dolphinfish in recent years, primarily to distinguish the colorful fish from the popular mammal.
No one knows exactly how the mahi mahi got the name dolphinfish. It may be because mahi mahi are often seen swimming with dolphins. Like the larger dolphin, flat-headed dolphinfish tend to jump out of the water when chasing their prey. Another reason may be that after death, dolphinfish lose their bright colors, turning gray, similar in color to the dolphin. Early fishermen may have misidentified the dead fish when they were brought onto boats.