The ocean sunfish or common mola (''Mola mola'') is one of the largest bony fish in the world. It was misidentified as the heaviest bony fish, which was actually a different species, ''

Mola alexandrini The giant sunfish or bumphead sunfish (''Mola alexandrini''), also known as the Ramsay's sunfish, southern sunfish, southern ocean sunfish, short sunfish or bump-head sunfish in many parts of the world,Diane J. Bray, 2011, Short Sunfish, or even ...

''. Adults typically weigh between . The

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

is native to

tropical The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referred to ...

and

temperate In geography, the temperate climates of Earth occur in the middle latitudes (23.5° to 66.5° N/S of Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout ...

waters around the world. It resembles a fish head without a tail, and its main body is flattened laterally. Sunfish can be as tall as they are long when their

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage * Dorsal c ...

and ventral

fins A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift or thrust, or provide the ability to steer or stabilize motion while traveling in water, air, or other fluids. Fin ...

are extended. Sunfish are generalist predators that consume largely small fish, fish larvae, squid, and crustaceans. Sea jellies and

salp A salp (plural salps, also known colloquially as “sea grape”) or salpa (plural salpae or salpas) is a barrel-shaped, planktic tunicate. It moves by contracting, thereby pumping water through its gelatinous body, one of the most efficient ...

s, once thought to be the primary prey of sunfish, make up only 15% of a sunfish's diet. Females of the species can produce more

eggs Humans and human ancestors have scavenged and eaten animal eggs for millions of years. Humans in Southeast Asia had domesticated chickens and harvested their eggs for food by 1,500 BCE. The most widely consumed eggs are those of fowl, especial ...

than any other known

vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () (chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with c ...

, up to 300,000,000 at a time. Sunfish fry resemble miniature pufferfish, with large pectoral fins, a tail fin, and body spines uncharacteristic of adult sunfish. Adult sunfish are vulnerable to few natural predators, but

sea lion Sea lions are pinnipeds characterized by external ear flaps, long foreflippers, the ability to walk on all fours, short and thick hair, and a big chest and belly. Together with the fur seals, they make up the family Otariidae, eared seals. ...

killer whale The orca or killer whale (''Orcinus orca'') is a toothed whale belonging to the oceanic dolphin family, of which it is the largest member. It is the only extant species in the genus ''Orcinus'' and is recognizable by its black-and-white ...

s, and

shark Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachi ...

s will consume them. Sunfish are considered a delicacy in some parts of the world, including Japan,

Korea Korea ( ko, 한국, or , ) is a peninsular region in East Asia. Since 1945, it has been divided at or near the 38th parallel, with North Korea (Democratic People's Republic of Korea) comprising its northern half and South Korea (Republic o ...

, and

Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia, at the junction of the East and South China Seas in the northwestern Pacific Ocean, with the People's Republic of China (PRC) to the northwest, Japan to the nort ...

. In the

European Union The European Union (EU) is a supranational political and economic union of member states that are located primarily in Europe. The union has a total area of and an estimated total population of about 447million. The EU has often been de ...

, regulations ban the sale of fish and fishery products derived from the family Molidae. Sunfish are frequently caught in

gillnets Gillnetting is a fishing method that uses gillnets: vertical panels of netting that hang from a line with regularly spaced floaters that hold the line on the surface of the water. The floats are sometimes called "corks" and the line with corks is ...

. A member of the order

Tetraodontiformes The Tetraodontiformes are an order of highly derived ray-finned fish, also called the Plectognathi. Sometimes these are classified as a suborder of the order Perciformes. The Tetraodontiformes are represented by 10 extant families and at least ...

, which also includes pufferfish,

porcupinefish Porcupinefish are fish belonging to the family Diodontidae (order Tetraodontiformes), also commonly called blowfish and, sometimes, balloonfish and globefish. They are sometimes collectively called pufferfish, not to be confused with the morpholo ...

, and filefish, the sunfish shares many traits common to members of this order. The ocean sunfish, ''Mola mola'', is the

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specime ...

of the

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

. __TOC__

Naming and taxonomy

Many of the sunfish's various names allude themselves to its flattened shape. Its scientific name, ''mola'', is Latin for "millstone", which the fish resembles because of its gray color, rough texture, and rounded body. Its common English name, sunfish, refers to the animal's habit of sunbathing at the surface of the water. Its common names in Dutch, Portuguese, French, Spanish, Catalan, Italian, Russian, Greek, Hungarian, Norwegian, and German (''maanvis'', ''peixe lua'', ''Poisson lune'', ''pez luna'', ''peix lluna'', ''Pesce luna'', ''рыба-луна'', ''φεγγαρόψαρο'', ''holdhal'', ''månefisk'' and ''Mondfisch'', respectively) mean "moon fish", in reference to its rounded shape. In German, the fish is also known as ''Schwimmender Kopf'', or "swimming head". In Polish, it is named ''samogłów'', meaning "head alone" or "only head", because it has no true tail. In Swedish, Danish and Norwegian it is known as ''klumpfisk'', in Dutch ''klompvis'', in Finnish ''möhkäkala'', all of which mean "lump fish". The Chinese translation of its academic name is , meaning "toppled wheel fish". The ocean sunfish has various superseded binomial synonyms, and was originally classified in the pufferfish genus, as '' Tetraodon mola''. It is now placed in its own

, ''Mola'', with three

: ''Mola mola,

Mola tecta ''Mola tecta'', the hoodwinker sunfish, belongs to the family Molidae and genus '' Mola''. It is closely related to the more widely known ocean sunfish (''Mola mola''). The Latin word "tecta" means hidden. The word "hidden" was adopted for the n ...

'' and ''

'' (previously known as ''Mola ramsayi''). The ocean sunfish, ''Mola mola'', is the

of the genus. The genus ''Mola'' belongs to the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Molidae. This family comprises three genera: ''

Masturus The sharptail mola (''Masturus lanceolatus'') is a species of mola found circumglobally in tropical and temperate waters. It is similar in appearance to the ocean sunfish (''Mola mola''), but can be distinguished by the projection on its clavus ...

'', '' Mola'' and '' Ranzania''. The common name "sunfish" without qualifier is used to describe the marine family Molidae and the freshwater sunfish in the family

Centrarchidae Centrarchidae, better known as sunfishes, is a family of freshwater ray-finned fish belonging to the order Perciformes (formerly belonging to the deprecated order Centrarchiformes), native only to North America. There are eight universally i ...

, which is unrelated to Molidae. On the other hand, the name "ocean sunfish" and "mola" refer only to the family Molidae. The family Molidae belongs to the order

, which includes pufferfish and filefish. It shares many traits common to members of this order, including the four fused teeth that form the characteristic beak and give the order its name ('=four, '=tooth, and '=shape). Indeed, sunfish fry resemble spiky pufferfish more than they resemble adult molas.

Description

Mola mola-Skelett, Naturhistorisches Museum Wien

The

caudal fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as ...

of the ocean sunfish is replaced by a rounded clavus, creating the body's distinct truncated shape. The body is flattened laterally, giving it a long oval shape when seen head-on. The pectoral fins are small and fan-shaped, while the dorsal fin and the anal fin are lengthened, often making the fish as tall as it is long. Specimens up to in height have been recorded. The mature ocean sunfish has an average length of and a fin-to-fin length of . The weight of mature specimens can range from , but even larger individuals are not unheard of. The maximum size recorded is in length, and maximum weight recorded is . The spinal column of ''M. mola'' contains fewer

vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristi ...

e and is shorter in relation to the body than that of any other fish. Although the sunfish descended from bony ancestors, its skeleton contains largely

cartilaginous Cartilage is a resilient and smooth type of connective tissue. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck a ...

tissues, which are lighter than

bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...

, allowing it to grow to sizes impractical for other bony fishes. Its teeth are fused into a beak-like structure, which prevents them from being able to fully close their mouths, while also having

pharyngeal teeth Pharyngeal teeth are teeth in the pharyngeal arch of the throat of cyprinids, suckers, and a number of other fish species otherwise lacking teeth.swim bladder. Some sources indicate the internal organs contain a concentrated neurotoxin,

tetrodotoxin Tetrodotoxin (TTX) is a potent neurotoxin. Its name derives from Tetraodontiformes, an order that includes pufferfish, porcupinefish, ocean sunfish, and triggerfish; several of these species carry the toxin. Although tetrodotoxin was discovere ...

, like the organs of other poisonous tetraodontiformes, while others dispute this claim.

Fins

In the course of its evolution, the caudal fin (tail) of the sunfish disappeared, to be replaced by a lumpy pseudotail, the clavus. This structure is formed by the convergence of the dorsal and anal fins, and is used by the fish as a rudder. The smooth-denticled clavus retains 12

fin ray Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as see ...

s and terminates in a number of rounded ossicles. Ocean sunfish often swim near the surface, and their protruding dorsal fins are sometimes mistaken for those of

s. However, the two can be distinguished by the motion of the fin. Unlike most fish, the sunfish swings its dorsal fin and anal fin in a characteristic sculling motion.

Skin

Adult sunfish range from brown to silvery-grey or white, with a variety of region-specific mottled skin patterns. Coloration is often darker on the dorsal surface, fading to a lighter shade ventrally as a form of countershading camouflage. ''M. mola'' also exhibits the ability to vary skin coloration from light to dark, especially when under attack. The skin, which contains large amounts of reticulated collagen, can be up to thick on the ventral surface, and is covered by denticles and a layer of

mucus Mucus ( ) is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both serous and mucous cells. It ...

instead of scales. The skin on the clavus is smoother than that on the body, where it can be as rough as sandpaper. More than 40 species of

parasite Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...

s may reside on the skin and internally, motivating the fish to seek relief in a number of ways. One of the most frequent ocean sunfish parasites is the flatworm '' Accacoelium contortum''. In temperate regions, drifting kelp fields harbor cleaner wrasses and other fish which remove parasites from the skin of visiting sunfish. In the tropics, ''M. mola'' solicits cleaning help from reef fishes. By basking on its side at the surface, the sunfish also allows seabirds to feed on parasites from its skin. Sunfish have been reported to breach, clearing the surface by approximately , in an apparent effort to dislodge embedded parasites.

Range and behavior

Ocean sunfish are native to the

and

waters of every ocean in the world. ''Mola'' genotypes appear to vary widely between the

Atlantic The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe an ...

and

Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the contine ...

, but genetic differences between individuals in the Northern and Southern hemispheres are minimal. Although early research suggested sunfish moved around mainly by drifting with ocean currents, individuals have been recorded swimming in a day at a cruising speed of . While this might be the case most of the time, they are also capable of moving rapidly when feeding or avoiding predators, to the extent that they can vertically leap out of water. Contrary to the perception that sunfish spend much of their time basking at the surface, ''M. mola'' adults actually spend a large portion of their lives actively hunting at depths greater than , occupying both the

epipelagic The photic zone, euphotic zone, epipelagic zone, or sunlight zone is the uppermost layer of a body of water that receives sunlight, allowing phytoplankton to perform photosynthesis. It undergoes a series of physical, chemical, and biological proc ...

and

mesopelagic The mesopelagic zone (Greek μέσον, middle), also known as the middle pelagic or twilight zone, is the part of the pelagic zone that lies between the photic epipelagic and the aphotic bathypelagic zones. It is defined by light, and begins at ...

zones.

Sunfish are most often found in water warmer than ; prolonged periods spent in water at temperatures of or lower can lead to disorientation and eventual death. Surface basking behavior, in which a sunfish swims on its side, presenting its largest profile to the sun, may be a method of "thermally recharging" following dives into deeper, colder water in order to feed. Sightings of the fish in colder waters outside of its usual habitat, such as those southwest of England, may be evidence of increasing marine temperatures, although the proximity of England's southwestern coast to the Gulf Stream means that many of these sightings may also be the result of the fish being carried to Europe by the current. Sunfish are usually found alone, but occasionally in pairs.

Feeding

The diet of the ocean sunfish was formerly thought to consist primarily of various

jellyfish Jellyfish and sea jellies are the informal common names given to the medusa-phase of certain gelatinous members of the subphylum Medusozoa, a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animals with umbrell ...

. However, genetic analysis reveals that sunfish are actually generalist predators that consume largely small fish, fish larvae, squid, and

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group can ...

s, with jellyfish and

s making up only around 15% of the diet. Occasionally they will ingest eel grass. This range of food items indicates that the sunfish feeds at many levels, from the surface to deep water, and occasionally down to the

seafloor The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth an ...

in some areas.

Lifecycle

Ocean sunfish may live up to ten years in captivity, but their lifespan in a natural habitat has not yet been determined. Their growth rate remains undetermined. However, a young specimen at the

Monterey Bay Aquarium Monterey Bay Aquarium is a nonprofit public aquarium in Monterey, California. Known for its regional focus on the marine habitats of Monterey Bay, it was the first to exhibit a living kelp forest when it opened in October 1984. Its biologists ...

increased in weight from and reached a height of nearly in 15 months. The sheer size and thick skin of an adult of the species deters many smaller predators, but younger fish are vulnerable to predation by

bluefin tuna Bluefin tuna is a common name used to refer to several species of tuna A tuna is a saltwater fish that belongs to the tribe Thunnini, a subgrouping of the Scombridae (mackerel) family. The Thunnini comprise 15 species across five genera, th ...

and mahi mahi. Adults are consumed by

orca The orca or killer whale (''Orcinus orca'') is a toothed whale belonging to the oceanic dolphin family, of which it is the largest member. It is the only extant species in the genus '' Orcinus'' and is recognizable by its black-and-white ...

s and

s. The mating practices of the ocean sunfish are poorly understood, but spawning areas have been suggested in the North Atlantic, South Atlantic, North Pacific, South Pacific, and Indian oceans. Females are estimated to be carrying as many as 300 million eggs, more than any other known vertebrate. Sunfish eggs are released into the water and externally fertilized by sperm. Newly hatched sunfish larvae are only long and weigh less than one gram. They develop into fry, and those which survive can grow up to 60 million times their original weight before reaching adult proportions, arguably the most extreme size growth of any vertebrate animal.Wood, The Guinness Book of Animal Facts and Feats. Sterling Pub Co Inc. (1983), Sunfish fry, with large pectoral fins, a tail fin, and body spines uncharacteristic of adult sunfish, resemble miniature pufferfish, their close relatives. Young sunfish

school A school is an educational institution designed to provide learning spaces and learning environments for the teaching of students under the direction of teachers. Most countries have systems of formal education, which is sometimes comp ...

for protection, but this behavior is abandoned as they grow.

Genome

In 2016, researchers from China National Genebank and

A*STAR The Agency for Science, Technology and Research (A*STAR) is a statutory board under the Ministry of Trade and Industry of Singapore. The agency supports R&D that is aligned to areas of competitive advantage and national needs for Singapore ...

Singapore, including Nobel laureate

Sydney Brenner Sydney Brenner (13 January 1927 – 5 April 2019) was a South African biologist. In 2002, he shared the Nobel Prize in Physiology or Medicine with H. Robert Horvitz and Sir John E. Sulston. Brenner made significant contributions to work ...

, sequenced the genome of the ocean sunfish and discovered several genes which might explain its fast growth rate and large body size. As member of the order Tetraodontiformes, like fugu, the sunfish has quite a compact genome, at 730 Mb in size. Analysis from this data suggests that sunfish and pufferfishes diverged approximately 68 million years ago, which corroborates the results of other recent studies based on smaller datasets.

Human interaction

Despite their size, ocean sunfish are docile and pose no threat to human divers. Injuries from sunfish are rare, although a slight danger exists from large sunfish leaping out of the water onto boats; in one instance, a sunfish landed on a 4-year-old boy when the fish leaped onto the boy's family's boat. Areas where they are commonly found are popular destinations for sport dives, and sunfish at some locations have reportedly become familiar with divers. They are more of a problem to boaters than to swimmers, as they can pose a hazard to watercraft due to their large size and weight. Collisions with sunfish are common in some parts of the world and can cause damage to the hull of a boat, or to the propellers of larger ships, as well as to the fish. The flesh of the ocean sunfish is considered a delicacy in some regions, the largest markets being Taiwan and Japan. All parts of the sunfish are used in cuisine, from the fins to the internal organs. Some parts are used in some areas of traditional medicine. Fishery products derived from sunfish are forbidden in the

according to Regulation (EC) No 853/2004 of the European Parliament and of the Council as they contain toxins that are harmful to human health. Sunfish are accidentally but frequently caught in drift gillnet fisheries, making up nearly 30% of the total catch of the swordfish fishery employing drift gillnets in California. The bycatch rate is even higher for the Mediterranean swordfish industry, with 71% to 90% of the total catch being sunfish. The fishery bycatch and destruction of ocean sunfish are unregulated worldwide. In some areas, the fish are "finned" by fishermen who regard them as worthless bait thieves; this process, in which the fins are cut off, results in the eventual death of the fish, because it can no longer propel itself without its dorsal and anal fins. The species is also threatened by floating litter such as plastic bags which resemble jellyfish, a common prey item. Bags can choke and suffocate a fish or fill its stomach to the extent that it starves. Many areas of sunfish biology remain poorly understood, and various research efforts are underway, including aerial surveys of populations, satellite surveillance using pop-off satellite tags, genetic analysis of tissue samples, and collection of amateur sighting data. A decrease in sunfish populations may be caused by more frequent bycatch and the increasing popularity of sunfish in human diet.

In captivity

Mola mola ocean sunfish Monterey Bay Aquarium 2

Sunfish are not widely held in aquarium exhibits, due to the unique and demanding requirements of their care. Some Asian aquaria display them, particularly in Japan. The Kaiyukan Aquarium in

Osaka is a designated city in the Kansai region of Honshu in Japan. It is the capital of and most populous city in Osaka Prefecture, and the third most populous city in Japan, following Special wards of Tokyo and Yokohama. With a population of ...

is one of few aquariums with ''M. mola'' on display, where it is reportedly as popular an attraction as the larger

whale shark The whale shark (''Rhincodon typus'') is a slow-moving, filter-feeding carpet shark and the largest known extant fish species. The largest confirmed individual had a length of .McClain CR, Balk MA, Benfield MC, Branch TA, Chen C, Cosgrove J, ...

s. The Lisbon Oceanarium in Portugal has sunfish showcased in the main tank, and in Spain, the Valencia Oceanogràfic has specimens of sunfish. The Ocean sunfish is also on display at the

Denmark ) , song = ( en, "King Christian stood by the lofty mast") , song_type = National and royal anthem , image_map = EU-Denmark.svg , map_caption = , subdivision_type = Sovereign state , subdivision_name = Kingdom of Denmark , establish ...

Nordsøen Oceanarium. In

Kamogawa Sea World Kamogawa Sea World is a large scale comprehensive marine leisure center/museum equivalent facility located between the Tojo coast and the national highway No. 128 in Kamogawa city, Chiba Prefecture, Japan. It is not affiliated with SeaWorld in a ...

the ocean sunfish named Kukey, who started captivity in 1982, set a world record for captivity for 2,993 days, living for eight years. Kukey was at the time of delivery, but was in size at the time of death. While the first ocean sunfish to be held in an aquarium in the United States is said to have arrived at the

in August 1986, other specimens have previously been held at other locations.

Marineland of the Pacific Marineland of the Pacific was a public oceanarium and tourist attraction located on the Palos Verdes Peninsula coast in Los Angeles County, California. Architect William Pereira designed the main structure. It was also known as Hanna-Barbera's ...

, closed since 1987 and located on the Palos Verdes Peninsula in Los Angeles County, California, held at least one ocean sunfish by 1961, and in 1964 held a specimen, said to be the largest ever captured at that time. However, another specimen was brought alive to Marineland Studios Aquarium, near St. Augustine, Florida, in 1941. Because sunfish had not been kept in captivity on a large scale before, the staff at Monterey Bay was forced to innovate and create their own methods for capture, feeding, and parasite control. By 1998, these issues were overcome, and the aquarium was able to hold a specimen for more than a year, later releasing it after its weight increased by more than 14 times. ''Mola mola'' has since become a permanent feature of the Open Sea exhibit. Monterey Bay Aquarium's largest sunfish specimen was euthanized on February 14, 2008, after an extended period of poor health. A major concern to curators is preventive measures taken to keep specimens in captivity from injuring themselves by rubbing against the walls of a tank, since ocean sunfish cannot easily maneuver their bodies. In a smaller tank, hanging a vinyl curtain has been used as a stopgap measure to convert a cuboid tank to a rounded shape and prevent the fish from scraping against the sides. A more effective solution is simply to provide enough room for the sunfish to swim in wide circles. The tank must also be sufficiently deep to accommodate the vertical height of the sunfish, which may reach . Feeding captive sunfish in a tank with faster-moving, more aggressive fish can also present a challenge. Eventually, the fish can be taught to respond to a floating target to be fed, and to take food from the end of a pole or from human hands.

References

External links

Research and info

FishBase reference

Australian Museum

OceanSunfish.org

Images and videos

Video lecture (16:53): ''Swim with giant sunfish in the open ocean''
- Tierney Thys * Skaphandrus.co
Mola mola photos
* {{Featured article ocean sunfish Pantropical fish ocean sunfish ocean sunfish