Ocean sunfish
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The ocean sunfish (Mola mola), also known as the common mola, is one of the largest bony fish in the world. It is the type species of the genus Mola, and one of five extant species in the family Molidae.<ref name="McClain"/><ref name="FishBase family"/> It was once misidentified as the heaviest bony fish, which was actually a different and closely related species of sunfish, Mola alexandrini.<ref name="Sawai2017"/> Adults typically weigh between Template:Convert. It is native to tropical and temperate 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 and ventral fins are extended.
Many areas of sunfish biology remain poorly understood,Template:Needs update and various research efforts are underway, including aerial surveys of populations,<ref name="LargePelagicsResearch">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> satellite surveillance using pop-off satellite tags,<ref name="OceanSunfishResearch">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="LargePelagicsResearch"/> genetic analysis of tissue samples,<ref name="OceanSunfishResearch"/> and collection of amateur sighting data.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
Adult sunfish are vulnerable to few natural predators, but sea lions, killer whales, and sharks will consume them. Sunfish are considered a delicacy in some parts of the world, including Japan, Korea, and Taiwan. In the European Union, regulations ban the sale of fish and fishery products derived from the family Molidae.<ref name="BannedinEEC">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Sunfish are frequently caught in gillnets.
NamingEdit
Its common English name, sunfish, refers to the animal's habit of sunbathing at the surface of the sea.Template:Citation needed 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 and Danish 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 Template:Lang-zh, meaning "toppled wheel fish". Many of the sunfish's various names allude to its flattened shape.Template:Citation needed
TaxonomyEdit
French polymath Guillaume Rondelet wrote about the ocean sunfish in his 1554 work de Piscibus, using the term Orthagoriscus,<ref>Template:Cite book</ref> "sucking pig" for the likeness of its body and mouth.<ref>Template:Cite journal</ref> It was originally classified in the pufferfish family as Tetraodon mola,<ref name="AnnotatedChecklist">Template:Cite journal</ref> its epithet mola is Latin for "millstone",<ref>Template:Cite dictionary</ref> which the fish resembles because of its gray color, rough texture, and rounded body.<ref name="ETYFish" /> It is now placed in its own genus Mola and family name Molidae<ref name="ETYFish">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> as the type species with two other species: Mola tecta and M. alexandrini (previously known as Mola ramsayi).<ref name="Bass2005"/> Extinct relatives of Mola mola lived in the Oligocene and Miocene epochs.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }} </ref> However, the earliest known fossil remains of Mola mola itself were found in archaeological middens dating to the Holocene epoch.<ref name="Porcasi2001"/>
The common name "sunfish" without qualifier is used to describe the marine family Molidae and the freshwater sunfish in the family Centrarchidae, which is unrelated to Molidae. On the other hand, the name "ocean sunfish" and "mola" refer only to the family Molidae.<ref name="McClain"/>
DescriptionEdit
It shares many traits common to members in the order Tetraodontiformes including pufferfish, porcupinefish, and filefish like having a beak formed from four fused teeth; sunfish fry resemble spiky pufferfish more than they resemble adult molas.<ref name="OceanSunfishEvolution">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
The caudal fin 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 Template:Convert in height have been recorded.<ref name="NZHeraldVisitor"/>
The mature ocean sunfish has an average length of Template:Convert and a fin-to-fin length of Template:Convert. The weight of mature specimens can range from Template:Convert,<ref name="McClain">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>Template:Cite journal</ref><ref>Template:Citation</ref> but even larger individuals are not unheard of. The maximum size recorded, a specimen washed ashore in New Zealand in 2006, was Template:Convert in length,<ref name="NZHeraldVisitor">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name=McClain2>Template:Cite journal</ref> with weighing Template:Convert.<ref name="McClain2" />
The spinal column of M. mola contains fewer vertebrae and is shorter in relation to the body than that of any other fish.<ref name="LargePelagicsLifeHistory">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Although the sunfish descended from bony ancestors, its skeleton contains largely cartilaginous tissues, which are lighter than bone, allowing it to grow to sizes impractical for other bony fishes.<ref name="LargePelagicsLifeHistory"/><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Its teeth are fused into a beak-like structure,<ref name="GomesPereira2022">Template:Cite journal</ref> which prevents them from being able to fully close their mouths, while also having pharyngeal teeth located in the throat.<ref>Template:Cite book</ref>
The axial musculature is completely lost during development. In addition they are missing a swim bladder. Instead they get their buoyancy from a stiff and gelatinous layer under the skin, which consist of about 90% water and a meshwork of collagen and elastin, acting like an exoskeleton. Due to its greasy texture, it may also contain lipids. The layer, which is horizontally separated by a septum, makes up a larger part of the animal's total mass the bigger the individual is.<ref name="LargePelagicsLifeHistory"/><ref>Template:Cite journal</ref> Some sourcesTemplate:Who indicate the internal organs contain a concentrated neurotoxin, tetrodotoxin, like the organs of other poisonous tetraodontiformes,<ref name="GomesPereira2022"/> while others dispute this claim.<ref name="OceanSunfishResearch"/>
FinsEdit
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,<ref name="StrangeTail">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="Leis'Conundrum">Template:Cite journal</ref> and is used by the fish as a rudder.<ref name="OnlineFieldGuide">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The smooth-denticled clavus retains 11–14 fin rays and terminates in a number of rounded ossicles.<ref name="AustMuseumAdult">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
Ocean sunfish often swim near the surface, and their protruding dorsal fins are sometimes mistaken for those of sharks.<ref name="NationalGeo"/> 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.<ref name="UnderwaterPioneer"/>
SkinEdit
Adult sunfish range from brown to silvery-grey or white, with a variety of region-specific mottled skin patterns.<ref name="McClain" /> 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.<ref name="McClain" /> The skin, which contains large amounts of reticulated collagen, can be up to Template:Convert thick on the ventral surface, and is covered by denticles and a layer of mucus instead of scales. The skin on the clavus is smoother than that on the body, where it can be as rough as sandpaper.<ref name="LargePelagicsLifeHistory"/>
More than 40 species of parasites may reside on the skin and internally, motivating the fish to seek relief in a number of ways.<ref name="McClain" /><ref name="AustMuseumAdult"/>Template:Clarify One of the most frequent ocean sunfish parasites is the flatworm Accacoelium contortum.<ref>Template:Cite journal</ref>
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 Template:Convert, in an apparent effort to dislodge embedded parasites.<ref name="NationalGeo">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
Distribution and habitatEdit
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Ocean sunfish are native to the temperate and tropical waters of every ocean in the world.<ref name="LargePelagicsLifeHistory"/> Mola genotypes appear to vary widely between the Atlantic and Pacific, but genetic differences between individuals in the Northern and Southern hemispheres are minimal.<ref name="TrackingSunfish"/>
Although early research suggested sunfish moved around mainly by drifting with ocean currents (which has resulted in the sunfish sometimes being characterized as a megaplankton<ref>Template:Cite book</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>), individuals have been recorded swimming Template:Convert in a day at a cruising speed of Template:Convert.<ref name="OnlineFieldGuide"/> 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 the fish 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 Template:Convert, occupying both the epipelagic and mesopelagic zones.<ref name="LargePelagicsPreliminary">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Sunfish are most often found in water warmer than Template:Convert;<ref name="LargePelagicsPreliminary"/> prolonged periods spent in water at temperatures of Template:Convert or lower can lead to disorientation and eventual death.<ref name="UnderwaterPioneer"/> 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.<ref name="TrackingSunfish"> {{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="Biogeography"> {{#invoke:citation/CS1|citation |CitationClass=web }}</ref> 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.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="BBC2012"/>
Sunfish are typically observed in solitary environments, though infrequently they may be encountered in pairs.<ref name="LargePelagicsLifeHistory"/>
FeedingEdit
The diet of the ocean sunfish was formerly thought to consist primarily of various jellyfish and other gelatinous zooplankton, such as ctenophores, salps, and medusae.<ref name="animaldiversity.org">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> However, genetic analysis reveals that sunfish are actually generalist predators that consume mostly small fish (such as flounder), fish (eel) larvae, squid, other molluscs, crustaceans, and other soft-bodied invertebrates, with jellyfish and salps making up only around 15% of the diet.<ref name="animaldiversity.org"/><ref name="Sousa2016"/> 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 in some areas.<ref name="McClain"/>
Life cycleEdit
Ocean sunfish may live up to ten years in captivity, but their lifespan in a natural habitat has not yet been determined.<ref name="NationalGeo"/> Their growth rate remains undetermined. However, a young specimen at the Monterey Bay Aquarium increased in weight from Template:Convert and reached a height of nearly Template:Convert in 15 months.<ref name="UnderwaterPioneer"/>
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 and mahi mahi. Adults are consumed by orca, sharks<ref name="LargePelagicsLifeHistory"/> and sea lions.<ref name="McClain" /><ref name="UnderwaterPioneer">Template:Cite book</ref>
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.<ref name="LargePelagicsLifeHistory"/> Females of the species can produce more eggs than any other known vertebrate,<ref name="McClain" /> up to 300 million at a time.<ref>Template:Cite journal</ref> Sunfish eggs are released into the water and externally fertilized by sperm.<ref name="AustMuseumAdult" />
Newly hatched sunfish larvae are only Template:Convert long and weigh less than one gram. They develop into fry that resemble miniature pufferfish, their close relatives.<ref name="AustMuseumAdult" /><ref name="FOGM_Mola">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Sunfish fry do not have the large pectoral fins and tail fin of their adult forms, but they have body spines uncharacteristic of adult sunfish, that disappear as they grow. Young sunfish school for protection, but this behavior is abandoned as they grow.<ref name="SwimWithSunfish" /> The fry that survive can grow up to 60 million times their original weight before reaching adult proportions,<ref name="OnlineFieldGuide" /> arguably the most extreme size growth of any vertebrate animal.<ref name="Wood">Wood, The Guinness Book of Animal Facts and Feats. Sterling Pub Co Inc. (1983), Template:ISBN</ref><ref>Kooijman, S. A. L. M., & Lika, K. (2013). Resource allocation to reproduction in animals. Am. Nat. subm, 2(06).</ref>
GenomeEdit
In 2016, researchers from China National Genebank and A*STAR Singapore, including Nobel laureate Sydney Brenner, 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.<ref>Template:Cite journal</ref>
ConservationEdit
The ocean sunfish is listed as vulnerable by the IUCN, with its population decreasing. Its main threat is the use of drift gillnets<ref name="IUCN2015"/>
Human interactionEdit
Despite their size, ocean sunfish are docile and pose no threat to human divers.<ref name="AustMuseumAdult" /> Injuries from sunfish are rare, although a slight danger exists from large sunfish leaping out of the water onto boats. In 2005, a Template:Convert-long sunfish landed on a 4-year-old boy when the fish leaped onto the boy's family's boat off the coast of Pembrokeshire, Wales, causing slight injuries.<ref name="BBC2005"/> Areas where they are commonly found are popular destinations for sport dives, and sunfish at some locations have reportedly become familiar with divers.<ref name="GomesPereira2022"/> 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,<ref name="Lulham2006"/> or to the propellers of larger ships, as well as to the fish.<ref name="AustMuseumAdult"/>
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.<ref name="OceanSunfishResearch"/> Some parts are used in some areas of traditional medicine.<ref name="GomesPereira2022"/> Fishery products derived from sunfish are forbidden in the European Union 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.<ref name="BannedinEEC" />
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.<ref name="OnlineFieldGuide" /> The bycatch rate is even higher for the Mediterranean swordfish industry, with 71% to 90% of the total catch being sunfish.<ref name="OceanSunfishResearch" /><ref name="SwimWithSunfish">Template:Cite video</ref>
A decrease in sunfish populations may be caused by more frequent bycatch and the increasing popularity of sunfish in human diet.<ref name="LargePelagicsLifeHistory"/> 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.<ref name="MolaFishery">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> 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.<ref name="NationalGeo"/>
In artEdit
Sarongs worn by women in Lamalera, a village in the island of Lembata in the Lesser Sunda Islands of Indonesia, have patterns of this fish; which they know as kebuku.<ref name="Barnes1988"/>
In captivityEdit
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.<ref name="UnderwaterPioneer"/> The Kaiyukan Aquarium in Osaka is one of few aquaria with Mola mola on display, where it is reportedly as popular an attraction as the larger whale sharks.<ref name="OsakaAquarium">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The Lisbon Oceanarium in Portugal has ocean sunfish showcased in the main tank,<ref name="Oceanario2019"/> and sunfish are also on display at the Denmark Nordsøen Oceanarium.<ref>Nordsøen Oceanarium: The Open Sea. Template:Webarchive Retrieved 8 December 2012.</ref>
In Kamogawa Sea World 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 Template:Convert at the time of delivery, but was Template:Convert in size at the time of death.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}Template:Dead link</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
While the first ocean sunfish to be held in an aquarium in the United States is said to have arrived at the Monterey Bay Aquarium in August 1986,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> other specimens have previously been held at other locations. Marineland of the Pacific, closed since 1987 and located on the Palos Verdes Peninsula in Los Angeles County, California, held at least one ocean sunfish by 1961,<ref name="Caldwell1964"/> and in 1964 held a Template:Convert specimen, said to be the largest ever captured at that time.<ref>Los Angeles Times. June 15, 1964. p. 3</ref> However, another Template:Convert specimen was brought alive to Marineland Studios Aquarium, near St. Augustine, Florida, in 1941.<ref>The Miami News, March 16, 1941, p. 5-C</ref>
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.<ref name="UnderwaterPioneer"/> Mola mola has since become a permanent feature of the Open Sea exhibit.<ref name="OnlineFieldGuide"/> Monterey Bay Aquarium's largest sunfish specimen was euthanized on February 14, 2008, after an extended period of poor health.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
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.<ref name="OsakaAquarium"/> 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.<ref name="UnderwaterPioneer"/> The tank must also be sufficiently deep to accommodate the vertical height of the sunfish, which may reach Template:Convert.<ref name="NZHeraldVisitor"/>
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,<ref name="Life in the slow lane"/>Template:Bsn and to take food from the end of a pole or from human hands.<ref name="UnderwaterPioneer"/>
ReferencesEdit
External linksEdit
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