It’s been described as a “swimming head,” and can weigh as much as an adult rhinoceros—and it also turns out to be one of the most fascinating fish in the sea

Diver Ryan Brennan hangs with a Mola mola off the coast of Southern California
Credit: Bradley Beckett

With a final breath of air, I descend beneath the surface among swaying kelp and flying sea lions. I’m in search of a creature that has eluded me for many years. As a freediver, I’ve met the humbling gaze of a tiger shark and tossed around seaweed with playful wild spotted dolphins. But I’ve never faced the puckered lips and buggy eyes of the whimsical Mola mola — a fish that can reach the weight of an adult rhinoceros.

Biologists have affectionately described Mola, or ocean sunfish, as a “a swimming head.” And while they seem to just float aimlessly at the surface, scientists are finding that these fish — which occupy a crucial evolutionary link in the fish family— are actually warming up after epic daily treks into deep water.

A testament to this bizarre nature, a viral video of the sunfish circulated in September of 2015. The expletive-shouting Boston fisherman is unsure if he’s witnessing a baby whale or sea turtle, two seemingly dissimilar animals. He’s not the only one.

These fish live off the California coast and around the world in temperate and tropical areas. But many people have never heard of them, let alone seen one.

Mola mola are not endangered and not eaten in the United States. In fact, females can produce up to 300 million eggs, more than any other bony fish. But the hapless fish ends up tangled in fishing nets, as bycatch for more valuable target species. They make up the largest bycatch component (29 percent) in the California drift-gillnet swordfish fishery.

So why does it matter if Mola mola are caught in mesh nets?

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