Mola mola

Geographic Range

Ocean sunfish, Mola mola , are found in the temperate and tropical regions of the Mediterranean, Atlantic, Indian, and Pacific Oceans (Wheeler, 1969; Sims and Southall, 2002; Houghton et al., 2006). They are commonly observed off the coast of Southern California, Indonesia, the British Isles, the Northern and Southern Isles of New Zealand, the southern coasts of Africa, and in the Mediterranean and occasionally in the North Sea (Muus, 1964; Ayling and Cox, 1982; Smith, 1965; Cartamil and Lowe, 2004; Houghton et al., 2006; Sims and Southall, 2002; Konow et al., 2006). Most sightings in the British Isles and North Sea occur during the summer months, particularly June and July, when the waters are between 13 and 17˚C (Sims and Southall, 2002). Ocean sunfish are thought to migrate to higher latitudes during the spring and summer months to pursue their migrating zooplankton prey (Liu et al., 2009).

• Biogeographic Regions
• indian ocean
  • native native
• atlantic ocean atlantic ocean
  • native native
• pacific ocean pacific ocean
  • native native
• mediterranean sea
  • native native

Habitat

Adult ocean sunfish are found in temperate and tropical oceans across the globe. They prefer the open ocean but occasionally venture into kelp beds and deep coral reefs in order to be cleaned of parasites by fishes such as wrasses ( Labroides dimidiatus and Thalasoma lunare ) and Emperor Angelfish (Hutchins, 2004; Humann and Deloach, 2002, Konow et al., 2006).

• Habitat Regions
• saltwater or marine saltwater or marine

• Aquatic Biomes
• pelagic pelagic

Physical Description

Ocean sunfish have a large body that is compressed and ovular. They are the largest bony fish, measuring up to 3.1 m in length, 4.26 m in height, and weighing up to 2235 kg (Hutchins, 2004; Humann and Deloach, 2002; Houghton et al., 2006). They are scale-less, and have a thick, rubbery skin and irregular patches of tubercles over their body (Hutchins, 2004; Wheeler, 1969; Smith, 1965). Notably, adult ocean sunfish do not have a caudal fin or caudal peduncle. They instead have a clavus, which is a truncated tail, used more like a rudder than for propulsion. The clavus reaches from the rear edge of the dorsal fin to the rear edge of the anal fin (Wheeler, 1969; Hutchins, 2004; Linnaeus, 1758). The dorsal and anal fins of ocean sunfish are tall, and their small pectoral fins point toward the dorsal fin (Hutchins, 2004). The dorsal fin has 15 to 18 soft rays, and the anal fin has 14 to 17 soft rays (Hutchins, 2004). They also have a small mouth with fused teeth that form a beak-like structure (Hutchins, 2004).

Ocean sunfish vary in coloration, though the head, back, tips of the anal and dorsal fins, and clavus are generally a mixture of dark grey-brown and dark silvery grey (Hutchins, 2004; Humann and Deloach, 2002; Ayling and Collins, 1982). They have a white belly and sometimes have white splotches on their fins and dorsal side (Ayling and Collins, 1982; Humann and Deloach, 2002). Adult ocean fish do not possess a lateral line, and only one gill opening is visible on each side, which is located near the base of the pectoral fins (Hutchins, 2004; Smith and Heemstra, 1986).

• Other Physical Features
• ectothermic ectothermic
• bilateral symmetry bilateral symmetry

Development

Ocean sunfish have two larval stages. Larvae in the first tetradon-like stage are round and spines protrude from the edges of their body. They have a well-developed tail and caudal fin (Bass et al., 2005; Muus, 1964) During the second larval stage, the tail is completely absorbed and spines disappear (Bass et al., 2005). Larvae generally measure about 0.25 cm in length (Pope et al., 2010). Juvenile ocean sunfish grow at an considerable rate, averaging 0.02 to 0.42 kg/day and sometimes reaching 0.82 kg/day (Pope et al., 2010).

Reproduction

Little is known about the mating systems of ocean fish, although they are thought to have paired courtship (Muus,1964; Hutchins, 2004). Some individuals are thought to spawn in the Sargasso Sea.

Little is known about the breeding behaviors of ocean sunfish. Off the coast of Japan, spawning is thought to occur between August and October (Nakatsubo et al., 2007). Female ocean sunfish can produce over 300 million eggs each breeding season, making them the most fecund extant vertebrate (Bass et al., 2005). Their eggs are very small, with an average diameter of 0.13 cm (Pope et al., 2010).

Little is known regarding parental investment of offspring in ocean sunfish.

Lifespan/Longevity

The lifespan of ocean sunfish is currently unknown. A member of the same family, sharptail mola are estimated to have a lifespan of 82 to 105 years (Liu et al., 2009).

Behavior

Ocean sunfish are generally solitary, although they are found in groups when being cleaned by other fish (Hutchins, 2004; Konow et al., 2006). Ocean sunfish use their dorsal and anal fins as their primary means of locomotion. They flap these fins in a synchronous motion, which also allows them to swim on their side (Hutchins, 2004). They occasionally swim near the surface, exposing their top fin, and may even jump out of the water in an apparent effort to detach parasites (Ayling and Cox, 1982; Humann and Deloach, 2002, Konow et al., 2006). Ocean sunfish have been observed repeated diving below the thermocline during the day, possibly to forage for zooplankton that migrate vertically (Cartamil and Lowe, 2004; Liu et al., 2009). They may also dive below the thermocline in order to avoid predators (Cartamil and Lowe, 2004). Ocean sunfish have also been observed basking at the surface of the water on their side, drifting with the ocean current. This may be an attempt to re-warm core body temperature after diving into colder water (Cartamil and Lowe, 2004).

• Key Behaviors
• natatorial natatorial
• motile motile
• solitary solitary

Home Range

Little is known regarding the home range of ocean sunfish.

Communication and Perception

Little is known regarding methods of communication and perception of ocean sunfish.

• Perception Channels
• tactile tactile
• chemical chemical

Food Habits

Ocean sunfish primarily feed on jellyfish and gelatinous zooplankton, such as ctenophores , salps , and medusae. They have also been known to eat soft bodied invertebrates, crustaceans , mollusks , seaweed, eel larvae, and even flounder (Wheeler, 1969). Ocean sunfish are thought to migrate to higher latitudes in response to zooplankton migrations during the spring and summer months (Liu et al., 2009). They may also migrate vertically during the day to prey upon jellyfish and zooplankton found below the thermocline (Cartamil and Lowe, 2004; Liu et al., 2009).

• Primary Diet
• herbivore herbivore
  • algivore
• planktivore planktivore

• Animal Foods
• fish
• mollusks
• aquatic crustaceans
• cnidarians
• zooplankton zooplankton

• Plant Foods
• macroalgae macroalgae

Predation

Ocean sunfish are often preyed upon by large sharks and California sea lions (Cartamil and Lowe, 2004). They may dive below the thermocline to avoid predators (Cartamil and Lowe, 2004). Ocean sunfish are also occassionally hunted by humans .

Ecosystem Roles

Ocean sunfish are considered to have strategic top-down control of jellyfish populations. They may also have a direct influence on the incidence and occurrence of jellyfish blooms (Liu et al., 2009).

• Ecosystem Impact
• keystone species keystone species

Economic Importance for Humans: Positive

Ocean sunfish are considered a delicacy in some Asian countries. They are also used in traditional Chinese medicines (Humann and Deloach, 2002).

• Positive Impacts
• food food
• body parts are source of valuable material

Economic Importance for Humans: Negative

Ocean sunfish are often caught as bycatch in commercial fishing nets, which can be a great inconvenience (Liu et al., 2009).

Conservation Status

Ocean sunfish have not been evaluated by the IUCN, US Federal List, or CITES. They are often caught as bycatch by drift gillnet fisheries. In southern California, ocean sunfish compromised 29% of the catch in drift gillnet fisheries targeting swordfish (Cartamil and Lowe, 2004). In the Mediterranean between 1992 and 1994, ocean sunfish had a bycatch rate of 70 to 93%. In South Africa, the bycatch rate of ocean sunfish is estimated at 17% (Liu et al., 2009).

Other Comments

Ocean sunfish, Mola mola , were originally described as Tetraodon mola by Linnaeus in his book, Systema Naturae 10th edition. Mola is the Latin word for millstone (Smith and Heemstra, 1986).

Additional Links

Encyclopedia of Life

Contributors

Brandon Griffin (author), Louisiana State University, Prosanta Chakrabarty (editor), Louisiana State University, Gail McCormick (editor), Animal Diversity Web Staff.

References

Ayling, T., G. Cox. 1982. Collins Guide to Sea Fishes of New Zealand . Auckland: William Collins Publishers LTD.

Bass, A., H. Dewar, T. Thys, J. Streelman, S. Karl. 2005. Evolutionary Divergence among lineages of the Ocean Sunfish family, Molidae (Tetraodontiformes). Marine Biology , 148: 405-414.

Campbell, A., J. Dawes. 2004. Triggerfishes and Allies. Pp. 259 in The New Encyclopedia of Aquatic Life , Vol. II, Fishes and Mammals Edition. China: The Brown Reference Group.

Cartamil, D., C. Lowe. 2004. Diel movement patterns of Ocean Sunfish Mola mola off Southern California. Mar. Ecol. Prog. Ser. , 266: 245-253.

Houghton, J., T. Doyle, J. Davenport, G. Hays. 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 , 86/5: 1237-1243.

Humann, P., N. Deloach. 2002. Odd-Shaped Swimmers. Pp. 419 in Reef Fish Identification of Florida, Caribbean, Bahamas , Vol. 2, 3rd Edition. Jacksonville: New World Publicators, Inc..

Hutchins, M. 2004. Tetraodontiformes. Pp. 477-478 in Grzimek’s Animal Life Encyclpedia , Vol. 5 fishes II, 2nd Edition. Detroit: Thompson Gale.

Konow, N., R. Fitzpatrick, A. Barnett. 2006. Adult Emperor Angelfish (Pomecanthus imperator) clean Giant sunfishes (Mola mola) at Nusa Lembongan, Indonesia. Coral Reefs , 25/2: 208.

Linnaeus, C. 1758. Sistema Naturae, 10th Edition .

Liu, K., M. Lee, S. Joung, Y. Chang. 2009. Age and growth estimates of the sharptail mola, Masturus lanceolatus,in waters of eastern Taiwan. Fisheries Research , 95/2-3: 154-160.

Migdalski, E., G. Fichter. 1976. The Fresh and Saltwater Fishes of the World . New York: Alfred Knopf.

Muus, B. 1964. . Collins Guide to the Sea Fishes of Britain and North-Western Europe . London: Collins Clear-Type Press.

Nakatsubo, T., M. Kawachi, N. Mano, H. Hirose. 2007. Spawning Period of Ocean Sunfish Mola mola in water of the eastern Kanto region, Japan. Aquaculture Science , 55/4: 613-618.

Pope, E., G. Hays, T. Thys, T. Doyle, D. Sims, N. Queiroz, V. Hobson, L. Kubicek, J. Houghton. 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.

Sims, D., E. Southall. 2002. Occurrence of ocean sunfish, Mola mola near fronts in the western English Channel. Journal of the Marine Biological Association of the UK , 82/5: 927-928.

Sims, D., N. Queiroz, T. Doyle, J. Houghton, G. Hays. 2009. Satellite tracking of the World's largest bony fish, the ocean sunfish (Mola mola L.) in the North East Atlantic. Journal of Experimental Marine Biology and Ecology , 370/1-2: 127-133.

Smith, J. 1965. The Sea Fishes of Southern Africa . South Africa: Central News Agency, LTD.

Smith, M., P. Heemstra. 1986. Smith’s Sea Fishes . Berlin: Springer-Verlag.

Wheeler, A. 1969. The Fishes of the British Isles and North-West Europe . Michigan: Michigan State University Press.