Mahi Mahi in the Atlantic vs Pacific: Are They the Same Fish?

It’s a fair question, since fisheries agencies clearly treat Atlantic and Pacific mahi mahi as separate things. NOAA maintains entirely separate pages, separate stock assessments, and separate management rules for each. Here’s what’s actually different, and what isn’t.

Same Species, Confirmed by Genetics

There’s no ambiguity on this point: every mahi mahi in every ocean is Coryphaena hippurus, the species Linnaeus described in 1758. A large-scale genome-wide study using roughly 8.7 million genetic markers plus full mitochondrial genome data confirmed there’s no separate species or subspecies involved anywhere in the world. Physically, an Atlantic-caught fish and a Pacific-caught fish are indistinguishable.

But Genetically Distinct Populations

What that same genetic research also revealed is more interesting: mahi mahi form four separate, genetically distinguishable population groups, corresponding almost exactly to the major ocean basins, the Atlantic, the Pacific, the Indian Ocean, and the Mediterranean Sea. These populations don’t interbreed in any meaningful way, likely because there simply isn’t enough natural movement of fish between ocean basins to mix their gene pools, despite mahi mahi being capable of migrating thousands of miles within a single basin.

Why That Difference Matters for Management

Because Atlantic and Pacific mahi mahi function as separate breeding populations, fisheries regulators manage them independently rather than as one global pool. In the United States, roughly a third of commercial mahi mahi harvest comes from the Atlantic, Gulf of Mexico, and Caribbean combined, while the majority comes from the Pacific, primarily around Hawaii. Within the Atlantic alone, U.S. regulators further divide the population into four separate stocks and stock complexes: South Atlantic, St. Croix, St. Thomas/St. John, and the Puerto Rico Dolphinfish Complex.

Regional Studies Are Refining This Further

Even within the Pacific, research has found finer-grained genetic structure than a single uniform population. A regional study in the tropical Eastern Pacific identified distinct genetic groups of mahi mahi within that one stretch of ocean alone, prompting discussion among fisheries scientists about whether management approaches need to get more localized than the current basin-wide model. The overall picture is a species that’s biologically uniform but structured into real, separately evolving populations at a scale finer than most people would assume for a fish that migrates thousands of miles in its own lifetime.