Ocean Sunfish

Mola mola

The largest bony fish, weighing up to 2 300 kilograms and reaching up to 3.3 metres in length. They have a brown, grey, or white body which may have a mottled pattern. Their body is a flattened oval shape with large dorsal and anal fins that they use like wings to swim. They don't have a tail fin but the joined edges of the dorsal and anal fins form a structure called a clavus that they use to steer with. Despite their unwieldy appearance, they can swim at speeds of 1.4 to 2.5 kilometres per hour - similar to other large fish.

Authority

Linnaeus, 1758

Classification Details

Phylum: Chordata (chordates); Subphylum: Vertebrata (vertebrates); Class: Actinopterygii (ray-finned fishes).

Habitat

Ocean sunfish are a pelagic (open ocean) species that occur worldwide. In the Atlantic Ocean, they are found from Newfoundland to South America. They spend most of their time underwater, following the movements of their prey, but are sometimes seen basking at the surface. They come into the coastal areas of the Bay of Fundy in summer and early fall.

Diet

Predators. Ocean sunfish feed on small fish, squid, crustaceans, cnidarians, and ctenophores. Their teeth are fused together, forming a beak-like mouth which they cannot fully close.

Reproduction

Sexes are separate. Females release eggs into the water and these are fertilized externally by the male's sperm. Females can release up to 300 million eggs at a time. Larval ocean sunfish appear completely different to adults, taking the form of sphere covered in spikes. Their reproductive cycle is not well-studied. We don't know how long ocean sunfish live, but it's possibly up to 20 years.

Fun Facts

The ocean sunfish is the world's largest bony fish. They also produce the largest number of eggs of any vertebrate.

Their common name may come from their habit of basking on the sea surface. This behaviour may help to warm them up after deep dives or attract birds to clean parasites from their skin.

References

Froese R and Pauly D (2020) FishBase. Mola mola (Linnaeus, 1758). Accessed through: World Register of Marine Species at: http://www.marinespecies.org/aphia.php?p=taxdetails&id=127405 Accessed online 22 January 2020.

Oceana. Ocean Sunfish – Ocean Fishes. https://oceana.org/marine-life/ocean-fishes/ocean-sunfish Accessed online 22 January 2020.

Pope EC, Hays GC, Thys TM, Doyle TK, Sims DW, Queiroz N, Hobson VJ, Kubicek L and Houghton JDR (2010) The biology and ecology of the ocean sunfish Mola mola: A review of current knowledge and future research perspectives. Reviews in Fish Biology and Fisheries 20(4), 471–487.

Robins CR and Ray GC (1986) Atlantic Coast Fishes: Peterson Field Guides. New York: Houghton Mifflin Company.

Scott WB and Scott MG (1988) Atlantic fishes of Canada. Canadian Bulletin of Fisheries and Aquatic Sciences 219, 731p.