Meet the Sunfish’s Cuter, Faster, More Agile Cousin

It’s a miniature version of the ocean’s derpiest fish.

Published June 16, 2017

The ocean sunfish—a goofy looking fish with a vacant gaze and toothy grin—is one of the most ridiculed animals in the sea. While some fish—the great white shark, the blue fin tuna, the sawfish—are met with awe or respect, the ocean sunfish, or Mola mola, commands a different reaction. “Oh my God, what the fuck is that, bro?” said one man from Boston, Massachusetts, upon his first encounter with the fish.

Living in the temperate and tropical zones of most of the world’s seas, ocean sunfish can grow up to 1.8 meters long and three meters tall, and weigh as much as a tonne. Marianne Nyegaard, a doctoral candidate at Murdoch University in Perth, Australia, says the ocean sunfish looks like a “suitcase with wings.”

Even as venerable an institution as National Geographic can’t help but ridicule the fish, calling them “clumsy swimmers,” before noting their awkwardly constructed mouths: “Their teeth are fused into a beak-like structure.” Ocean sunfish can’t close their mouths—they are the mouth-breathers of the sea.

Just look at it swim. Video by Rems Production/videoblocks

But new research by Nyegaard and her colleagues shines a different light on the sunfish, or at least its family tree.

As it turns out, the oft-dissed ocean sunfish has a smaller, more agile cousin that is surprising scientists with its ability to hunt some of the ocean’s faster species.

“Their wings are so small, but they are fast,” says Nyegaard. Nearly every muscle in the body of this smaller sunfish—known as the slender sunfish—is geared toward powering those tiny fins.

Where the larger sunfish feeds by sucking up jellyfish, Nyegaard and her colleagues have found evidence that these smaller sunfish prey on squid.

“The species that these guys eat, from a family called Ommastrephidae, are very fast. They are like race cars of the squid world,” she says.

Nyegaard says the larger ocean sunfish can move quickly after an extended period of acceleration. Sometimes, she says, ocean sunfish can move fast enough to breach the water before flopping back over again. But slender sunfish, which measure from 60 to 80 centimeters in length, are like rockets by comparison.

The discovery came by way of a fisherman in Australia, who found a slender sunfish with the remains of 17 squid in its belly. He made the catch right after the Fukushima Daiichi nuclear power plant disaster in 2011. “He thought it was a mutant fish from radiation,” Nyegaard says.

Speed and hunting prowess aside, Nyegaard says slender sunfish share many features with their better-known cousins. They have roughly the same shape: a body like a blunted axe, and fins sticking out of the top and bottom of their head. Slender sunfish also can’t close their mouth.

“The slender sunfish is really cute,” Nyegaard says. “They swim around the ocean like blowup dolls.”

Slender sunfish, like ocean sunfish, are found in warm water habitats all around the world’s seas.

Slender sunfish are known to eat crustaceans and fish. But Evgeny Romanov, a marine biologist with the Centre Technique d’Appui à la Pêche Réunionnaise, on the French island of Réunion, says he’s not surprised slender sunfish can eat squid, since they’re such energetic swimmers.

Even a slow slender sunfish is a formidable hunter. In 2014, Romanov published a study on a slender sunfish that didn’t have an anal fin. Lacking its rear fin, the fish was slow in the water, but it was still able to hunt.

The slender sunfish is fast, agile, and an adept hunter. The ocean sunfish is none of these things. But at the end of the day, the ocean sunfish needs these traits about as much as it needs a bicycle.

Power and beauty may be our main ways of judging the animal world, but evolution has an extended set of criteria. The two sunfish are the way they are because they operate within very different niches. Given both species are found globally, they must be pretty good at what they do. The ocean sunfish is awkward, hulking, and slow—but it’s the best version of itself in the sea.