Ocean Sunfish (Mola mola)

The ocean sunfish (Mola mola) is the largest bony fish species in the world. This fish is also one of the strangest-looking fish in the world - it looks like half of its body is missing.

Ocean sunfish are also known as mola molas (or simply, molas) for their scientific name - the word mola is Latin for 'millstone,' in reference to the fish's circular shape. A millstone is a heavy, disk-shaped stone used to grind grain. Ocean sunfish may also be called moonfish.

Ocean sunfish can grow to be over 10 feet across and weigh over 5,000 pounds (Source: Oceansunfish.org).

Ocean sunfish are a disc-shaped, flat fish that have a large dorsal fin and ventral fin, two pectoral fins, big eyes, a small mouth and a narrow, scalloped 'tail' (called a clavus). Unlike most other fish, the sunfish doesn't have scales, but a tough, elastic skin that may be covered with up to 40 different kinds of parasites.

Their figures appear less than hydrodynamic, but despite this, ocean sunfish are capable of leaping clear of the water.

Ocean sunfish are gray to white in color, and may have a spotted, Appaloosa-like appearance.

• Kingdom: Animalia
• Phylum: Chordata
• Class: Actinopterygii
• Order: Tetraodontiformes
• Family: Molidae
• Genus: Mola
• Species: mola

Ocean sunfish are in the Order Tetraodontiformes, which means they are related to puffer and porcupine fishes. The name Tetradontiformes refers to the 'beak' found in these fish, which has 4 fused teeth. Ocean sunfish are in the Family Molidae, which includes 3 other species of sunfish - the slender mola (Ranzania laevis), sharp-tailed mola (Masterus lanceolutus) and southern ocean sunfish (Mola ramsayi).

Even though they may look more primitive than other fish, recent research suggests that the sunfish family was one of the more recent fish families to come about. While modern fish evolved about 100 million years ago, ocean sunfish didn't come about until about 50 million years ago.

Ocean sunfish are found in tropical and temperate waters of the Atlantic, Pacific, Mediterranean and Indian Oceans. You can see an interesting map of sunfish sightings reported by 'citizen scientists' here.

Sunfish are often seen at the water surface, lying on their side as if they are basking in the sun. Scientists have suggested that this may be to warm up after deep dives in cold water, to recover their stores of oxygen, or to encourage cleaning of the skin or parasite removal by seabirds or fish.

Sunfish can swim to at least 1,500 feet (Source: FishBase.org.) A tagging study in the Atlantic Ocean reported that sunfish spent more time in the ocean depths during the day and were closer to the ocean surface at night. When the tagged fish were in warmer waters (e.g., in the Gulf Stream), they spent more time at depth, presumably spending longer amounts of time looking for food.

The tagging study also found that sunfish tagged in the Gulf of Maine sometimes made long treks all the way to the Gulf of Mexico, probably in response to cooling winter water temperatures and the need to go to warmer waters to find prey.

Ocean sunfish eat jellyfish, plankton, algae, mollusks, brittle stars and small fish.

Ocean sunfish reproduce by releasing eggs and sperm into the water. Ocean sunfishes have tiny eggs, but they have many more than most fish species - in fact, one ocean sunfish was estimated to have more than 300 million eggs in one ovary. When larvae hatch, they have spikes and resemble pufferfishes.

Ocean sunfish are harmless to people, and they are not a common food fish - their flesh may contain toxins. However, some sources (e.g., a living marine resources guide to Somalia) say that it is a delicacy.

Want to see an ocean sunfish? You might have to get wet. The only aquarium in the U.S. with an ocean sunfish exhibit is the Monterey Bay Aquarium in California. You might have a chance to see a sunfish in the wild if you go on a fishing, boating or whale watching excursion off the west or east coast of the U.S. Have you seen a sunfish in the wild? Where? I'd love to hear about your sighting.

References

• FishBase. Family Molidae - Molas or Ocean Sunfishes. Accessed September 22, 2011.
• Houghton, J.D.R., et.al. 2006. The ocean sunfish Mola mola: insights into distribution, abundance and behaviour in the Irish and Celtic Seas. Journal of the Marine Biological Association of the United Kingdom. Accessed September 25, 2011.
• McGrouther, M. 2011. Ocean Sunfish. Australian Museum. Accessed September 25, 2011.
• Monterey Bay Aquarium. Ocean Sunfish. Accessed September 22, 2011.
• National Geographic. Ocean Sunfish. Accessed September 25, 2011.
• Oceansunfish.org. 2010. Evolution. Accessed September 25, 2011.
• Potter, I.F., Howell, W.H.. 2010. Vertical movement and behavior of the ocean sunfish, Mola mola, in the northwest Atlantic. J. Exp. Mar. Biol. Ecol., doi:10.1016/j.jembe.2010.10.014. Accessed September 25, 2011.
• Thomas, Abbie. Sunfish Seekers. ABC Science. Accessed September 25, 2011.
• Whitty, Julia. 2010. Mola mola. Deep Blue Home Blog. Accessed September 25, 2011.