The common mola holds several records in the world of bony fishes:
- The species produces the heaviest fish on record, weighing up to 2.3 tn (2.5 t.).
- It produces the most eggs—more than 300 million at a time!
- It grows 60 million times larger during the brief period from hatching to adulthood.
- In one case, a captive common mola was observed to have grown 364 kg (800 lb.) in only 14 months.
The common mola has a disc-shaped body with two long fins, one dorsal (on its back) and one ventral (on its abdomen). Sea lions in California have been observed biting off these fins and tossing the fish around like a Frisbee. Scientists wonder if the sea lions do this in order to soften the fish's tough, sandpapery skin before eating it.
The common mola is normally silver in colour, but it can darken when stressed. It can reach 4 m (11 ft.) in length.
The common mola is also called the ocean sunfish. The name refers to the fishes' habit of lying on the surface with one broad side exposed to the sun. They do this to warm up before diving to hunt.
Common molas eat mainly jellyfish. They "chew" them by sucking them in so that the jellyfish gets caught on special teeth (pharyngeal teeth) in their throat. The fish then alternately sucks and spits the jellyfish, thereby shredding it on the teeth.
Unfortunately, common molas also eat floating plastic bags because they mistake them for jellyfish. When they suck them in, the bags can get caught in their throat and the fish suffocate.
The common mola hosts many parasites: more than 40 species are known to live on this species. Some of these parasites even have their own parasites! Common molas have been seen jumping out of the water, leaping up to three body lengths above the surface. It is thought that they do this in order to knock off their parasites.
The main predators of the common mola are sea lions and killer whales. They are also commonly caught by accident in commercial fishing nets.
Common molas are found in the open ocean of the Atlantic, Indian, Pacific and Southern oceans. They bask at the surface and dive occasionally in order to feed.