ocean sunfish

A slender mola washed up at the research station that I worked at this summer. My buddy juan took this shot. These fish are gorgeous and are a pelagic fish that rarely come up into our temperate waters. This is another sure sign of an El Niño year here in California

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They grow to about a meter which is nothing compared to some of the other members of the molidae family. 

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This big guy is a Mola mola, also known as an ocean sunfish and they grow to weights over 1000kg! 

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Gone in one gulp! The tiny “by-the-wind-sailors” that have been appearing on area beaches also happen to be a favorite snack of the enormous ocean sunfish (Mola mola), which can grow to be the size of a small car! (photo by Jodi Frediani)

By-the-wind sailors (Velella velella) are actually hydroid polyps—jelly-like invertebrates.The “sail” helps propel the animal on its journey across the ocean. In late spring and early autumn, hundreds of thousands of these drifting sailors wash up on the beaches of Northern California. 

The velella stays on the surface of the open ocean for most of its life. To remain buoyant in the ocean, it has a series of sealed air chambers in its float. They travel in groups of thousands, and capture small fish with short tentacles that have stinging cells dangling underwater. (Although their sting is strong enough to stun a tiny animal, a human being would barely feel it.)

Learn more about the ocean sunfish


The beautiful purple-striped jelly is best appreciated from a safe distance! Though not fatal, its sting can be painful. In spite of this, ocean sunfish have been seen munching on these jellies and are thought to be immune to their sting. If you’re not an ocean sunfish, you can still safely see purple-striped jellies in our Open Sea wing!

Thank you to P.J. Taylor for the photo!

How far does a mola travel? Our ocean sunfish are routinely released in the Monterey Bay when they reach about 400 pounds. At that time they’re tagged, to help us learn more about mola behavior in the wild. One of our recently tagged fish was just spotted by staff on a NOAA research vessel, off Point Conception on the California coast—a distance of 120 miles, which it covered in 10 days!

Normally, these tags are released and begin transmitting data after a programmed period of time, so it  was pure luck to see this animal swimming at the surface with the tag attached.

It’s likely that this mola mola is just beginning its long journey– tagged fish have transmitted data from as far south as the tip of Baja!

Learn more about ocean sunfish research at the Aquarium

(Charlene Boarts photo)

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In other news yesterday an ocean sunfish (Mola mola) washed up on a nearby beach and NOBODY WANTED IT so we snatched it and spent the morning dissecting it for science.

Our ocean sunfish was a juvenile male, under three feet in length and with a distinct but underdeveloped testis. Females are slightly (but this is up for debate) larger, and when fully grown, are among the most fecund animals known to man, with some individuals seen to be carrying up to 300 million eggs at a time.

All guts are shifted forwards, to make space for the giant anal and dorsal fin muscles, which move oppositely to propel the fish. They are quite powerful, and can even launch it out of the water like a breaching whale.

Ocean sunfish are also home to upwards of 40 species of parasites at any given time, a picture which I did not include because I care about you. Trust me when I say that if I had that many tapeworms in my liver, that particular organ would not have remained within me for very long. Even if I had to use my bare hands.

Also their caudal fin is completely degenerated through lack of use, and what’s left is called a clavus. Also, as I learned today, is the first thing to become horrifyingly decomposed to a gelatinous liquid after they die.

Anyway, we gave him a decent burial (“decent” is loosely defined here) and in about a year everything but the bones will be gone, after which he’ll be shamelessly exhumed and put on display!

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The ocean sunfish, Mola mola, or common mola, is the heaviest known bony fish in the world. It has an average adult weight of 1,000 kg. The species is native to tropical and temperate waters around the globe. The diet of the ocean sunfish consists primarily of various jellyfish. It also consumes salps, squid, crustaceans, small fish, fish larvae, and eel grass. Ocean sunfish are vulnerable to few natural predators, but sea lions, orcas and sharks will consume them.

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