Fish Identification: Mola Mola (Sunfish)

The ocean sunfish, or mola mola, as it is most often called, is a fascinating sea creature. Their odd appearance and enormous size makes them a popular attraction at aquariums around the world.

Physical description

Mola mola are big. Really big. In fact, it's the heaviest known bony fish in the world. Sunfish, on average, weigh well over a ton (1,000 kg), and are almost 6 feet (2 m) in length. There have been sightings of mola mola over twice these sizes, though.

Sunfish look like some kind of freak accident. Their bodies resemble a lump of poorly molded clay with a fin on the top and bottom. The body is flattened vertically (imagine a vertical pancake).

The dorsal and anal fin are particularly large, make the entire fish as tall as it is long. It also has small, fan-shaped pectoral fins. The mola mola doesn't have a proper caudal fin, and instead has a lumpy tail.

Geography and habitat

Sunfish live across the globe in tropical and temperate regions.

They can swim deep (up to 2,000 ft, or 600 m), and actually spend most of their lives at deep depths. This, combined with their presence mostly in open waters, makes them a rare sighting on dives. If you've ever seen one while scuba diving, consider yourself quite lucky.

Sunfish have an interesting behavior that is the source of their name. They will occasionally swim close to the surface and turn horizontal, exposing the large side of their body to the sun. This basking behavior is thought to "thermally charge" the fish in preparation for diving to deep, cold water.

Overall, very little is known about mola mola.

Further reading

Monterey Bay Aquarium

Photos by Ilse Reijs and Jan-Noud Hutten and Dan Hershman