Fish
Mahi-mahi
Coryphaena hippurus · also called dolphinfish, dorado, common dolphinfish
The mahi-mahi lives its whole life at a sprint. It hatches from a speck, reaches a metre inside a year, spawns every few days, and is usually dead of old age by four. Along the way it is one of the most beautiful fish in the ocean — a fact that lasts only as long as the fish does.
Overview
Coryphaena hippurus roams the warm surface waters of every ocean, often around floating weed and debris that gather prey. It is electric blue-green and gold in life, with males growing a tall blunt forehead. It hunts flying fish, squid, and small pelagic fish.
Fast life, short life
The mahi-mahi is among the fastest-growing fish known, reaching a metre and maturity in four to five months. Most live only two to four years, spawning every few days once mature. That rapid turnover makes its fisheries more resilient than those of slow fish like tuna.
The colour that dies
Its colours are controlled by living cells and pulse when the fish is excited. Within minutes of death they fade to dull grey — a transformation sailors have remarked on for centuries.
Not a dolphin
Called dolphinfish for centuries, it is unrelated to the mammal; the Hawaiian name mahi-mahi (“very strong”) was adopted on menus to end the confusion.
Status
The mahi-mahi is Least Concern and abundant. The main concern in its fisheries is bycatch of turtles, sharks, and juvenile tuna.
Mahi-mahi: common questions
Is mahi-mahi a dolphin?
No. Mahi-mahi is a ray-finned fish, and it has nothing to do with dolphins, which are mammals. The confusion comes from its old English name, dolphinfish, which is centuries old and appears in the logs of sailing ships that watched the brightly coloured fish ride their bow waves the way dolphins do. When the fish became popular on North American menus in the twentieth century, restaurants adopted the Hawaiian name mahi-mahi specifically so that diners would not think they were being served dolphin. In Spanish-speaking regions it is dorado; in much of the Pacific it is still simply called dolphinfish or dolphin by anglers.
Why does a mahi-mahi lose its colour when it dies?
The vivid blues and golds are produced by light interacting with layered reflective cells and pigment cells in the skin, and the fish actively controls them, flushing and shifting the colours in response to excitement, hunting, and social signalling. That control depends on living nerves and cells. As the fish dies, the cells lose their organisation and the reflective structures collapse, and the colour drains away to a flat grey-yellow within a few minutes. Anglers describe a hooked mahi-mahi at the side of the boat as strobing through blue, green, and gold, and then going dull almost as soon as it is brought aboard.
How can a fish grow so fast?
Mahi-mahi live fast in every sense. They inhabit warm, food-rich surface water, they eat almost constantly, much of it energy-dense prey like flying fish and squid, and they put that energy straight into growth rather than storing it. They mature in a matter of months and then spawn repeatedly, so their whole biology is tuned to producing the next generation quickly before predators or old age catch up. The trade-off is a very short life. From a fisheries point of view this is good news; a stock that turns over in two or three years can rebuild from overfishing far faster than a shark or a tuna that takes a decade or more to mature.
Is mahi-mahi sustainable to eat?
Generally it is one of the better choices among ocean fish, for the biological reasons above; its fast growth and high reproductive rate make the stocks relatively hard to deplete, and several fisheries are certified or rated favourably. The main caveats are about how it is caught. Longline fisheries targeting mahi-mahi can hook sea turtles, sharks, and seabirds, and fish aggregating devices used to concentrate mahi-mahi also gather juvenile tuna and other species. Troll- and pole-caught mahi-mahi, and fish from well-managed regional fisheries, are the lower-impact options.