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Why are ocean sunfish causing beach closures?

Matthew Lawrence, Stellwagen Bank NMS, NOS, NOAA/National Oceanic and Atmospheric

On two consecutive summer afternoons this week, South Shore beaches have been cleared by reports of a shark in the water — maybe even a great white.

And on two consecutive afternoons, the creature in question turned out to be an ocean sunfish. Though the harmless plankton feeder might look like a great white as it floats with its fin in the air, the two species could scarcely be more different below the surface.

Both of the scares came in the wake of Monday’s confirmed great white sighting off of the coast of Duxbury, and marine experts say it’s appropriate to be cautious when it comes to shark safety at beaches.


PHOTOS: Shark sighting near Mass. beach

But the sunfish — along with the basking shark, which startled people in the Taunton River Wednesday — is a frequent culprit in false alarms about predatory sea creatures. It’s also an interesting specimen in its own right.

It’s the world’s heaviest bony fish

The sunfish can grow to weigh more than a ton. Though other animals in the sea can be larger, those that are fish — like the whale shark — have cartilage instead of bones. Those that have bones — like the blue whale — aren’t fish.

Its skin is poison

The sunfish doesn’t have many natural enemies, which probably has something to do with the fact that its skin is slightly toxic if eaten. That means the fish is generally very friendly. When in captivity, they often swim right up to aquarium staff or divers. They don’t have much interest in fishing lures.

Mark Smith, vice president of animal care at the New England Aquarium, described sunfish as “sweethearts.”

“They don’t have much of a sense of self-preservation,” he said.

People eat it anyway

Smith said the sunfish has lots of connective tissue, and of course the toxic skin, but there are muscular parts that people can eat. He says he hasn’t tried it, but he’s heard from people who say it’s very tasty.


According to the National Oceanic and Atmospheric Administration, people eat many parts of the fish in Japan and other places, including internal organs.

Smith said the sunfish is related to the fugu, which is a Japanese puffer fish that must be prepared by specially trained chefs because parts of its body are more than 1,000 times more poisonous than cyanide.

It’s not related to the tiny “sunfish” found in freshwater lakes.

We’re not talking about this kind of sunfish.AP

It goes by various names

You could properly refer to the sunfish as the mola, or mola mola, which is its scientific name — derived from the Latin for “millstone.” That could have something to do with its thin, flat shape.

In some European languages it is known as “moon fish.”

It likes to hang out near the surface

Nobody knows exactly why, but Smith said it could very well have something to do with the heat from the sun. Sunfish do prefer warm climates to cold ones.

“It looks like they’re sunbathing,” Smith said.

But another possible explanation, he said, is a mutually beneficial relationship with seagulls. Smith said the birds have been observed eating parasites off of sunfish.

It still looks scary

It’s probably best to get out of the water if you see this:

Marshfield Police

Even though it might not be this:

Massachusetts State Police

The image of the sunfish at the top of this page was used under a Creative Commons license. Some rights are reserved.