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Ocean Sunfish: Diving with the Mola Mola

Ocean Sunfish: Diving with the Mola Mola

Written by Scuba.com
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Published on June 6, 2023
ocean sunfish mola mola underwater with scuba diver
TAGS: fish

The ocean sunfish is one of the ocean’s least understood species, although it is by no means a stranger to people of the world. Its scientific name, Mola mola, derives from the Latin word for “millstone,” a reference to the resemblance of the fish to the grey, rough, rounded surface of a millstone.

The names for the ocean sunfish are translated to “moon fish,” “swimming head,” “head alone,” and “toppled car fish” — all in reference to its peculiar physical makeup.

ocean sunfish mola mola underwater
Image via Shutterstock

What is the ocean sunfish (mola mola)?

It is commonly known in English as the ocean sunfish, so named for the basking behavior it displays near the surface of waters across the globe. Indeed, although well-known, the ocean sunfish is anything but common. The family from which the ocean sunfish hails falls under the order of Tetraodontiformes, which includes pufferfish and blowfish, giving it similar facial features to these species.

Characteristics

The bizarrely-shaped fish is flat and has no tail fin, but rather a rounded, sometimes scalloped, tail end. Its dorsal and anal fins, found on the top and bottom of the fish, are its only means of propulsion throughout the water column. This species grows to Goliath proportions — and is one of the biggest fish in the ocean — with an average length of 6 feet and weight of more than 2,000 pounds. In the wild, the ocean sunfish can be as tall, fin to fin, as it is long, if not taller. Even with these dimensions, it is a docile species and poses no threat to humans in the water.

Habitat

A pelagic species, the ocean sunfish is native to tropical and temperate waters of the entire planet. However, it does spend the majority of its time in depths of 660 feet to 2,000 feet. You can find it in the Mediterranean or even Florida. Curiously, its existence relies on specific temperatures. If it is subjected to waters colder than 50F for a prolonged time, it will suffer disorientation and eventual death.

Behavior

Despite the depth range it typically prefers, however, the ocean sunfish is most widely known for rising to the surface, laying flat on its side, seemingly soaking up the warm rays of the sun. It has also been observed breaching the surface, with distances recorded at three times the fish’s body length! Although the exact purpose of these behaviors is not known, it is thought that perhaps it is to remove parasites. By drifting on its side, the ocean sunfish presents its parasite-riddled skin to seabirds, while breaching has been observed in other fish species as a way to dislodge parasites through force.

Diet

Contrary to its massive size, the ocean sunfish subsists on a diet that is nutritionally poor, which means the animal must consume enormous amounts of food to sustain its weight. The primary food source for the ocean sunfish is jellyfish, as well as squid, crustaceans, small fishes, fish larvae, and even grasses — a testament to the various depths it will go to feed.

ocean sunfish mola mola underwater with scuba diver
Image via Shutterstock

Predators

Preying on jellyfish makes it a valuable component of ocean ecosystems, as it helps to regulate populations of jellies in many areas to avoid invasive swarms. Although the ocean sunfish generally enjoys life unencumbered by predators, species such as sharks and orcas will prey upon it, and sea lions have been observed preying on the fish simply for sport, tearing away its fins and abandoning the rest of the creature to die on the seafloor.

It is seemingly docile towards humans and many divers have enjoyed the company of the Ocean sunfish while Scuba diving. The fish however is not so loved by boaters as there have been instances of sunfish colliding with boats while surfacing causing significant damage to the boats. Ocean sunfish can even jump out the water at the surface up to a height 10 feet (3 meters) in the air and land with a splash to shake off parasites that infest their skin. A story of a boy that got knocked off his boat when a sunfish leaped onto it is quite popular among other such incidents.

Fishing

While humans are another of its deliberate predators, ocean sunfish have been experiencing population decline mostly as a result of being the unfortunate by-catch of gillnet fishing operations. It has been reported that the ocean sunfish makes up 30 percent of the total allowable catch (TAC) for a swordfish fishery in California, while the Mediterranean swordfish industry reports that it comprises 70 to 90 percent of their TAC. There are currently no fisheries regulations in place for the ocean sunfish.

The meat of ocean sunfish is also considered a delicacy places like Taiwan and Japan and they are fished for even their fins and internal organs that are used in traditional medicine. The Mola Mola is also threatened by floating litter such as plastic bags which resemble jellyfish, its main diet causing them to choke and suffocate.

Conclusion

This clumsy but fascinating fish as gigantic as it is, still seems like only half a fish instead of a whole making it one bizarre looking fish!

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