What is an Ocean Sunfish?

J.L. Drede

The ocean sunfish is a large fish of the Molidae family found in temperate and tropical waters around the world. Other frequently used names for the fish are the common mola and mola mola. It is the heaviest of all bony fish. Specimen of the fish have been caught weighing almost 5,000 pounds (2,267 kg), measuring 14 feet (4 meters) vertically and 10 feet (3 meters) across. The mola name is latin for millstone, which is what the fish can resemble when seen from the surface.

Saltwater sunfish feed on squid.
Saltwater sunfish feed on squid.

In addition to its incredible size, the ocean sunfish is also notable for its very unusual body shape. The body of the fish is shaped like a giant bullet, never curtailing in the back to form a proper rear fin. In fact, its back fin never grows from birth on, and actually folds back into itself as the fish ages. Accentuating the odd shape of the fish are two large pectoral fins, one at back and one on the bottom. Its coloration is usually bland, most often this fish is gray and white with light color patterns.

Ocean sunfish are found in tropical waters around the world.
Ocean sunfish are found in tropical waters around the world.

The large fin sometimes gets the ocean sunfish mistaken for a shark, but unlike some species of shark, the mola is usually harmless to humans. It may have a massive body, but the mouth of the ocean sunfish is small by comparison. Its diet usually includes small jellyfish, squid, sponges and crustaceans. Small fish and eel larvae have also been found in examined specimens. Because of its massive size, the mola does not have many predators. Tuna and other fish may feed on mola larvae, but the only predators of the fish one it reaches a notable size are sea lions and orcas.

Instead of predators, a common cause for concern with the mola is parasites. More than 40 different parasites are known to make a home both internally and on the body of the ocean sunfish. These parasites dig in the rough exterior of the fish, causing discomfort and irritation. The sunfish becomes infected with so many parasites through its life that it will frequently bask itself near the ocean surface, letting small fish and even birds feed off of the parasites covering its body.

The mola mola is not an aggressive fish, and human divers can usually swim alongside it with little worry of injury. However, the massive size of the fish can sometimes lead to accidental injury, occasionally there are reports of jumping sunfish landing on, and injuring, people. The sunfish's massive size can also damage boats that accidentally ram into the creature while it is basking to remove parasites.

Orcas are natural predators of the ocean sunfish.
Orcas are natural predators of the ocean sunfish.

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