10 Amazing Facts About Ocean Sunfish

Mola Mola - Ocean Sunfish

 Stephen Frink/Getty Images

The sea is filled with unusual creatures, and the ocean sunfish is certainly one of them. This bony fish, also known as the common mola, is famous for its enormous bulk, striking appearance, and high fertility.

The Ocean Sunfish Is the World's Largest Bony Fish

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, making them the largest bony fish species.

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

The Ocean Sunfish Is Also Known as the Mola Mola

Underwater view of mola mola, ocean sunfish, Magadalena bay, Baja California, Mexico

 Rodrigo Friscione/Getty Images

The ocean sunfish's scientific name is Mola mola. The word "mola" is Latin for millstone—a large round stone used to grind grain—and the fish's name is a reference to its disc-like shape. Ocean sunfish are often referred to as mola molas, or simply molas.

The ocean sunfish is also known as the common sunfish, as there are three other species of sunfish that live in the ocean—the slender mola, the sharp-tailed mola, and the southern ocean sunfish.

Ocean Sunfish Don't Have Tails

Ocean sunfish (Mola mola) found in open ocean, California, USA, Eastern Pacific Ocean

Mark Conlin/Getty Images 

When you look at an ocean sunfish, you might notice that its back end appears to be missing. The fish doesn't have a normal-looking tail. Instead, it has a lumpy appendage called a clavus, which formed through the fusion of the fish's dorsal and anal fin rays. Despite its lack of a powerful tail, the ocean sunfish is still capable of leaping out of the water.

Ocean Sunfish May Be Brown, Gray, White, or Spotted

Indonesia, Bali, Nusa Penida, Crystal Bay, Ocean Sunfish (Mola mola)

 Dave Fleetham/Getty Images

Ocean sunfish vary in color from brown to gray to white. Some even have spots, like the fish shown here.

Ocean Sunfish Love to Eat Jellyfish

Ed Bierman/Flickr

Ocean sunfish like to eat jellyfish and siphonophores (relatives of jellyfish). They also eat salps, small fish, plankton, algae, mollusks, and brittle stars.

Ocean Sunfish Are Found Throughout the World

Huge ocean sunfish, (Mola mola), Azores

 Jens Kuhfs/Getty Images

Ocean sunfish live in tropical and temperate waters, and they can be found in the Atlantic, Pacific, Mediterranean, and Indian Oceans. To see an ocean sunfish, though, you'll likely have to find one in the wild, 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 the fish are kept at only a few other aquaria, such as the Lisbon Oceanarium in Portugal and the Kaiyukan Aquarium in Japan.

Ocean Sunfish Sometimes Look Like They Are Playing Dead

Sunfish, Mola mola, Molidae, Witless Bay Ecological Reserve, Newfoundland, Canada

Barrett&MacKay Barrett&MacKay/Getty Images 

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 near the ocean surface, sometimes flapping their dorsal fins. There are a few theories about why sunfish do this; they may undertake long, deep dives in cold water in search of their favorite prey, and may use the warm sun at the surface to re-heat themselves and aid digestion (research published in 2015 lent support to this theory). The fish may also use the warm, oxygen-rich surface water to recharge their oxygen stores. Most interestingly, they may visit the surface to attract seabirds from above or fish from below to clean their skin of parasites. Some sources suggest that the fish wave their fins to attract the birds.

Ocean Sunfish Spend More Time Near the Ocean Surface at Night

Split level shot showing what is happening above and below the waterline as a sunfish swims on the water's surface with a diver in the background.

by wildestanimal/Getty Images 

From 2005 to 2008, scientists tagged 31 ocean sunfish in the North Atlantic in the first study of its kind. The tagged sunfish spent more time near the ocean surface during the night than during the day—and spent more time in the deep when they were in warmer waters such as the Gulf Stream and the Gulf of Mexico.

Ocean Sunfish Are Highly Fertile

Ocean Sunfish, Mola Mola, Bali Island, Indo-Pazific, Indonesia

 Franco Banfi/Getty Images

An ocean sunfish was once found with an estimated 300 million eggs in her ovary—more than scientists have ever found in any vertebrate species. Although sunfish produce many eggs, the eggs are tiny and essentially scattered into the water, making their chances of survival relatively small. Once an egg is fertilized, the embryo grows into a tiny spiked larvae with a tail. After hatching, the spikes and tail disappear and the baby sunfish resembles a small adult.

Ocean Sunfish Are Harmless to Humans

Ocean Sunfish and Diver, Mola Mola, Bali Island, Indo-Pazific, Indonesia

 Franco Banfi/Getty Images

Despite their enormous size, ocean sunfish are harmless to humans. They move slowly and are likely more frightened of us than we are of them. Because they are not considered a good food fish in most places, their biggest threats are likely being hit by boats and being caught as by-catch in fishing gear. Their biggest natural predators are orcas and sea lions.