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10 Facts About Ocean Sunfish

Learn About the World's Largest Bony Fish


Even as marine life go, the ocean sunfish is a strange-looking creature. Learn more about this fish - one of the ocean's biggest - below.


1. The ocean sunfish is the largest bony fish species.

Ocean sunfish in the near of Bali. Relaxing in warm water. Cleaning station.
Jens Kuhfs/ Photographer's Choice/ Getty Images

The largest ocean sunfish ever measured was over 10 feet across, and weighed close to 5,000 pounds. On average, ocean sunfish weigh about 2,000 pounds. This makes them the largest bony fish species.

Bony fish have skeletons of bone, which distinguishes them from cartilaginous fish, whose skeletons are made of cartilage.

With their large eyes and relatively small mouth, the ocean sunfish shown here almost looks surprised at its size!

2. The ocean sunfish may also be called the Mola mola.

Ocean Sunfish / Dianna Schulte, Blue Ocean Society for Marine Conservation
© Dianna Schulte, Blue Ocean Society for Marine Conservation

The ocean sunfish's scientific name is Mola mola. What does 'mola' mean? It is Latin for millstone, which is a large, heavy round stone used to grind grain. So, the ocean sunfish's scientific name is a reference to the fish's disk-like shape. Because of their scientific name, ocean sunfish are often referred-to as 'mola molas,' or simply, molas. Anyway, isn't the word 'mola' more fun to say than ocean sunfish?

This species may also be called the common sunfish, as there are other species of sunfish that live in the ocean - 3 to be exact - the slender mola (Ranzania laevis), sharp-tailed mola (Masterus lanceolutus) and southern ocean sunfish (Mola ramsayi).

3. Ocean sunfish don't have a tail.

Ocean Sunfish / Dianna Schulte, Blue Ocean Society for Marine Conservation
© Dianna Schulte, Blue Ocean Society for Marine Conservation
When you look at an ocean sunfish, you might notice that it appears that its back end is missing. These fish don't really have a normal-looking tail. Instead, they have an appendage called a clavus, which is a result of the fusion of dorsal and anal fin rays. Despite their lack of a powerful tail, ocean sunfish are capable of breaching (leaping) clear of the water!

4. Ocean sunfish may be brown, gray, white or spotted in color.

Ocean Sunfish / Dianna Schulte, Blue Ocean Society for Marine Conservation
© Dianna Schulte, Blue Ocean Society for Marine Conservation
An ocean sunfish's color can vary from brown to gray or silvery, or even almost white. They may also have spots, like the fish shown here.

5. The preferred food of ocean sunfish are jellyfish.

Ocean sunfish like to eat jellyfish. They will also eat salps, small fish, plankton, algae, mollusks, brittle stars.

6. Ocean sunfish are found throughout the world.

Ocean Sunfish / exfordy, Flickr
Courtesy exfordy, Flickr

Ocean sunfish live in tropical and temperate waters, and they may be found in the Atlantic, Pacific, Mediterranean and Indian Oceans. To see an ocean sunfish, you'll likely have to find one in the wild, though, because they are difficult to keep in captivity. The Monterey Bay Aquarium is the only aquarium in the U.S. to have live ocean sunfish, and ocean sunfish are kept at only a few other aquaria, such as the Lisbon Oceanarium in Portugal and the Kaiyukan Aquarium in Japan.

It is possible to see ocean sunfish in the wild, though, especially if you're out on a boat. They are a frequent sighting on whale watches in the Gulf of Maine, for example.

7. Sunfish may look like they're 'playing dead' when you see them.

Ocean Sunfish / Moosealope, Flickr
Courtesy Moosealope, Flickr

If you're lucky enough to see an ocean sunfish in the wild, it may look like it's dead. That's because ocean sunfish are often seen lying on their sides at the surface, sometimes flapping their dorsal fin.  There are a few theories on why sunfish do this.  They may undertake long, deep dives in cold water in search of their favorite prey, jellyfish, and may use the warm sun at the surface to re-heat themselves and aid digestion. They may also use the warm, oxygen-rich surface water to recharge their oxygen stores. And most interestingly, they may be at the surface to attract seabirds from above or fish from below to clean their skin of parasites. Some sources suggest that the waving of the fin is what is used to attract the birds.

8. Sunfish may spend more time at the ocean surface at night.

From 2005-2008, scientists tagged 31 ocean sunfish in the North Atlantic in the first study of its kind. This study made many interesting discoveries about ocean sunfish - the tagged sunfish spent more time at the ocean surface during the night than during the day, and spent even more time at depth when they were in warmer water, such as when they were in the Gulf Stream or the Gulf of Mexico. The researchers proposed that this might be due to spending more time at depth looking for food when the fish were in relatively warmer water.

9. Ocean sunfish are one of the most fertile species.

One ocean sunfish was found with an estimated 300 million eggs in her ovary - this is more than ever found in any other vertebrate species. Although sunfish produce lots of eggs, the eggs are tiny, and are basically scattered into the water, so their chances of survival are relatively small.  If an egg is fertilized, the embryo grows into a tiny, spiked lavae, that even has a tail.  It hatches at about 2mm in size, and eventually the spikes and tail disappear and the sunfish looks like a small adult.

10. Ocean sunfish are not dangerous to humans.

California Sea Lion (Zalophus californianus) Picture
© Jennifer Kennedy, Blue Ocean Society for Marine Conservation
Despite their enormous size, ocean sunfish are harmless to humans. They move slowly, and in fact are likely more threatened by us then we are of them - since they are not considered a good food fish in most places, their biggest threats are likely being hit by boats and being caught as bycatch in fishing gear. As far as natural predators, parasites, orcas, and sea lions seem to be the biggest culprits.
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