Theocean sunfish (Mola mola), also known as thecommon mola, is one of the largestbony fish in the world. It is thetype species of the genusMola, and one of three extant species in the familyMolidae.[6][7] It was formerly misidentified as the heaviest bony fish, which is actually a different and closely related species of sunfish,Mola alexandrini.[8] Adults typically weigh between 247 and 1,000 kg (545 and 2,205 lb). It is native totropical andtemperate 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 (about 5.9 ft) when theirdorsal and ventralfins are extended.
Many areas of sunfish biology remain poorly understood, including mating practices and spawning locations, early life stages, movement and migration patterns, population structure and status, diet and trophic ecology, and post-release survival rates,[needs update] and various research efforts are underway, including aerial surveys of populations,[9] satellite surveillance using pop-offsatellite tags,[10][9] genetic analysis of tissue samples,[10] and collection of amateur sighting data.[11]
The ocean sunfish is one of the largestbony fish. It has a flattened body and is as tall as it is long (about 5.9 ft.).
Its common English name, sunfish, refers to the animal's habit of sunbathing at the surface of the sea.[citation needed] Its common names in Catalan, Dutch, French, German, Greek, Hungarian, Italian, Norwegian, Portuguese, Russian, Spanish, and Ukrainian (peix lluna,maanvis,Poisson lune,Mondfisch,φεγγαρόψαρο,holdhal,Pesce luna,månefisk,peixe lua,рыба-луна,pez luna, andриба-місяць, respectively) mean "moon fish", in reference to its rounded shape. In German, the fish is also known asSchwimmender Kopf, or "swimming head". In Polish, it is namedsamogłów, meaning "head alone" or "only head", because it has no true tail. In Swedish and Danish it is known asklumpfisk, in Dutchklompvis, in Finnishmöhkäkala, all of which mean "lump fish". The Chinese translation of its academic name is翻車魚;fān chē yú, meaning "toppled wheel fish". Many of the sunfish's various names allude to its flattened shape.[citation needed]
French polymathGuillaume Rondelet wrote about the ocean sunfish in his 1554 workde Piscibus, using the termOrthagoriscus,[13] "sucking pig" for the likeness of its body and mouth.[14] It was originally classified in the pufferfish family asTetraodon mola,[15] its epithetmola is Latin for "millstone",[16] which the fish resembles because of its gray color, rough texture, and rounded body.[17] It is now placed in its own genusMola and family nameMolidae[17] as thetype species with two other species:Mola tecta andM. alexandrini (previously known asMola ramsayi).[18] Extinct relatives ofMola mola lived in theOligocene andMiocene epochs.[19] However, the earliest known fossil remains ofMola mola itself were found in archaeologicalmiddens dating to theHolocene epoch.[1]
The common name "sunfish" without qualifier is used to describe themarine family Molidae and thefreshwater sunfish in the familyCentrarchidae, which is unrelated to Molidae. On the other hand, the name "ocean sunfish" and "mola" refer only to the family Molidae.[6]
A sunfishfry, which still possesses spines that will later disappearA skeleton, showing the structure of the fins
The ocean sunfish shares many traits common to members in theorderTetraodontiformes , includingpufferfish,porcupinefish, andfilefish , like having a beak formed from four fused teeth; sunfishfry resemble spiky pufferfish more than they resemble adult molas.[20]
Thecaudal fin of the ocean sunfish is replaced by a roundedclavus, 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 3.3 m (10 ft 10 in) in height have been recorded.[21]
The mature ocean sunfish has an average length of 1.8 m (5 ft 11 in) and a fin-to-fin length of 2.5 m (8 ft 2 in). The weight of mature specimens can range from 247 to 1,000 kg (545 to 2,205 lb),[6][22][23] but even larger individuals are not unheard of. The maximum size recorded, a specimen washed ashore in New Zealand in 2006, was 3.3 m (10 ft 10 in) in length,[21][24] weighing 2,300 kg (5,100 lb).[24]
The spinal column ofM. mola contains fewervertebrae and is shorter in relation to the body than that of any other fish.[25]Although the sunfish descended frombony ancestors, its skeleton contains largelycartilaginous tissues, which are lighter thanbone, allowing it to grow to sizes impractical for other bony fishes.[25][26] Its teeth are fused into a beak-like structure,[27] which prevents them from being able to fully close their mouths, while also havingpharyngeal teeth located in the throat.[28]
The axial musculature is completely lost during development. In addition, they are missing aswim bladder. Instead, they get their buoyancy from a stiff and gelatinous layer under the skin, which consists 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.[25][29] Some sources[who?] indicate the internal organs contain a concentratedneurotoxin,tetrodotoxin, like the organs of other poisonous tetraodontiformes,[27] while others dispute this claim.[10]
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,[30][31] and is used by the fish as a rudder.[32] The smooth-denticled clavus retains 11–14fin rays and terminates in a number of rounded ossicles.[33]
Ocean sunfish often swim near the surface, and their protruding dorsal fins are sometimes mistaken for those ofsharks.[34] 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 characteristicsculling motion.[35]
Adult sunfish range from brown to silvery-grey or white, with a variety of region-specific mottled skin patterns.[6] 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.[6] The skin, which contains large amounts of reticulated collagen, can be up to 7.3 cm (2+3⁄4 in) thick on the ventral surface, and is covered bydenticles and a layer ofmucus instead ofscales. The skin on the clavus is smoother than that on the body, where it can be as rough as sandpaper.[25]
More than 40 species ofparasites may reside on the skin and internally, motivating the fish to seek relief in a number of ways.[6][33][clarification needed] One of the most frequent ocean sunfish parasites is the flatwormAccacoelium contortum.[36]
In temperate regions, drifting kelp fields harborcleaner wrasses and other fish that 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, while smaller parasite-eating fish feed on the underside. Sunfish have been reported tobreach, clearing the surface by approximately 3 m (10 ft), in an apparent effort to dislodge embedded parasites.[34][37]
Although early research suggested sunfish moved around mainly by drifting with ocean currents (which has resulted in the sunfish sometimes being characterized as amegaplankton[39][40]), individuals have been recorded swimming 26 km (16 mi) in a day at a cruising speed of 3.2 km/h (1.7 kn).[32] 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 200 m (660 ft), occupying both theepipelagic andmesopelagic zones.[41] Sunfish are most often found in water warmer than 10 °C (50 °F);[41] prolonged periods spent in water at temperatures of 12 °C (54 °F) or lower can lead to disorientation and eventual death.[35] 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.[38][42] 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.[43][44]
Sunfish are typically observed in solitary environments, though infrequently they may be encountered in pairs.[25]
The diet of the ocean sunfish was formerly thought to consist primarily of variousjellyfish and othergelatinous zooplankton, such asctenophores,salps, andmedusae.[45] However, genetic analysis reveals that sunfish are actually generalist predators that consume mostly small fish (such asflounder), fish (eel) larvae,squid, othermolluscs,crustaceans, and other soft-bodied invertebrates, with jellyfish and salps making up only around 15% of the diet.[45][46] Occasionally, they will ingesteel grass. This range of food items indicates that the sunfish feeds at many levels, from the surface to deep water, and occasionally down to theseafloor in some areas.[6]
Ocean sunfish may live up to ten years in captivity, but their lifespan in a natural habitat has not yet been determined.[34] Their growth rate also remains undetermined. However, a young specimen at theMonterey Bay Aquarium increased in weight from 26 to 399 kg (57 to 880 lb) and reached a height of nearly 1.8 m (5 ft 11 in) in 15 months.[35]
The sheer size and thick skin of an adult of the species deters many smaller predators, but younger fish are vulnerable to predation bybluefin tuna andmahi mahi. Adults are consumed byorca,sharks[25] andsea lions.[6][35]
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.[25] Females of the species can produce moreeggs than any other knownvertebrate,[6] up to 300million at a time.[47] Sunfish eggs are released into the water andexternally fertilized by sperm.[33]
Newly hatched sunfish larvae are only2.5 mm (3⁄32 in) long and weigh less than one gram. They develop intofry that resemble miniaturepufferfish, their close relatives.[33][48] Sunfishfry do not have the large pectoral fins and tail fin of their adult forms, but they have body spines uncharacteristic of adult sunfish, which disappear as they grow. Young sunfishschool for protection, but this behavior is abandoned as they grow.[49] The fry that survive can grow up to 60 million times their original weight before reaching adult proportions,[32] arguably the most extreme size growth of any vertebrate animal.[50][51]
In 2016, researchers from China National Genebank andA*STAR Singapore, including Nobel laureateSydney 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, likefugu, the sunfish has quite a compact genome, at 730Mb 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.[52]
A sunfish caught in 1910, with an estimated weight of 1,600 kg (3,500 lb)
Despite their size, ocean sunfish are docile and pose no threat to human divers.[33] Injuries from sunfish are rare, although a slight danger exists from large sunfish leaping out of the water onto boats. In 2005, a 1 metre (3 feet 3 inches)-long sunfish landed on a 4-year-old boy when the fish leaped onto the boy's family's boat off the coast ofPembrokeshire, Wales, causing slight injuries.[53] Areas where they are commonly found are popular destinations for sport dives, and sunfish at some locations have reportedly become familiar with divers.[27] 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,[54] or to the propellers of larger ships, as well as to the fish.[33]
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 areused in cuisine, from the fins to the internal organs.[10]Some parts are used in some areas of traditional medicine.[27] Fishery products derived from sunfish are forbidden in theEuropean 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.[12]
Sunfish are accidentally but frequently caught indrift gillnet fisheries, making up nearly 30% of the total catch of theswordfish fishery employing drift gillnets in California.[32] Thebycatch rate is even higher for the Mediterranean swordfish industry, with 71% to 90% of the total catch being sunfish.[10][49]
A decrease in sunfish populations may be caused by more frequent bycatch and the increasing popularity of sunfish in human diet.[25] 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.[55]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.[34]
Sarongs worn by women in Lamalera, a village in the island ofLembata in the Lesser Sunda Islands of Indonesia, have patterns of this fish; which they know askebuku.[56]
In 2015, local fishermen Michael Bergin and Jason Foster inBoston Harbor misidentified an ocean sunfish variously (and enthusiastically) as a sea turtle, a baby whale—pronounced like "baby wheel"—a tuna,Moby Dick, and a flounder, and reported it to thecoast guard, in a video replete with a profanity-laden Boston accent[57]which led to their brief fame[58][59][60][61][62]and a lasting impression in Boston cultural memory.[63][64][65][66][67][68]
A tank at theMonterey Bay Aquarium provides a size comparison between an ocean sunfish and humans.
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.[35] TheKaiyukan Aquarium inOsaka is one of few aquaria withMola mola on display, where it is reportedly as popular an attraction as the largerwhale sharks.[69]TheLisbon Oceanarium in Portugal has ocean sunfish showcased in the main tank.[70]
InKamogawa 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 72 cm (2.36 ft) at the time of delivery, but was 187 cm (6.14 ft) in size at the time of death.[71][72]
While the first ocean sunfish to be held in an aquarium in the United States is said to have arrived at theMonterey Bay Aquarium in August 1986,[73] 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,[74] and in 1964 held a 290-kilogram (650 lb) specimen, said to be the largest ever captured at that time.[75] However, another 450-kilogram (1,000 lb) specimen was brought alive to Marineland Studios Aquarium, near St. Augustine, Florida, in 1941.[76]
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.[35]Mola mola has since become a permanent feature of the Open Sea exhibit.[32] Monterey Bay Aquarium's largest sunfish specimen was euthanized on February 14, 2008, after an extended period of poor health.[77]
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.[69] 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.[35] The tank must also be sufficiently deep to accommodate the vertical height of the sunfish, which may reach 3.2 m (10 ft 6 in).[21]
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,[78][better source needed] and to take food from the end of a pole or from human hands.[35]
^abLiu, J.; Zapfe, G.; Shao, K.-T.; Leis, J.L.; Matsuura, K.; Hardy, G.; Liu, M.; Robertson, R.; Tyler, J. (2016) [errata version of 2015 assessment]."Mola mola".IUCN Red List of Threatened Species.2015 e.T190422A97667070. Retrieved11 July 2024.
^Gudger, Eugene W.; MacDonald, Samuel M. (November 1935). "The Rarest of the Ocean Sunfishes".The Scientific Monthly.41 (5):396–408.Bibcode:1935SciMo..41..396G.JSTOR16070.
^Lewis, Charlton T.; Short, Charles (1879)."mola".A Latin Dictionary. Perseus Digital Library.
^abScharpf, Christopher; Lazara, Kenneth J. (12 June 2023)."Family TETRADONTIFORMES"(PDF).The ETYFish Project. Archived fromthe original(PDF) on 30 October 2023. Retrieved25 October 2023.
^Nakatsubo, Toshiyuki; Kawachi, Masahiro; Mano, Nobuhiro; Hirose, Hitomi (2007), "Estimation of Maturation in Wild and Captive Ocean SunfishMola mola",水産増殖 (in Japanese),55 (2):259–264,doi:10.11233/aquaculturesci1953.55.259,ISSN0371-4217
^Johnson, G. David; Britz, Ralf (October 2005). "Leis' Conundrum: Homology of the Clavus of the Ocean Sunfishes. 2. Ontogeny of the Median Fins and Axial Skeleton ofRanzania laevis (Teleostei, Tetraodontiformes, Molidae)".Journal of Morphology.266 (1):11–21.Bibcode:2005JMorp.266...11J.doi:10.1002/jmor.10242.PMID15549687.S2CID43363353.We thus conclude that the molid clavus is unequivocally formed by modified elements of the dorsal and anal fin and that the caudal fin is lost in molids.
^Freedman, Jonathan A.; Noakes, David L.G. (2002). "Why are there no really big bony fishes? A point-of-view on maximum body size in teleosts and elasmobranchs".Reviews in Fish Biology and Fisheries.12 (4):403–416.Bibcode:2002RFBF...12..403F.doi:10.1023/a:1025365210414.S2CID36649270.
^Gaffin, Adam (August 8, 2021)."Baby wheel rescued at East Boston shore".Universal Hub.Archived from the original on 2021-08-09. Retrieved2025-09-17.TheNew England Aquarium reports its divers rescued an ocean sunfish, also known as a mola mola and, at least in the Boston area, as a baby wheel,…
^Blumenthal, Rachel Leah; Lewis, Wyndham; Cain, Jacqueline (August 2025)."The Ultimate (and Unabridged) Guide to New England Seafood".Boston.Boston Globe Media.Archived from the original on 2025-09-09. Retrieved2025-09-17.B is for "Baby F***in' Whale!"—In 2015, two guys from Malden went fishing in Boston Harbor and encountered something that would make them internet famous: a sunfish. But Michael Bergin and his buddy Jason Foster didn't know that's what they were looking at—and their five minutes of pure, unfiltered Boston bewilderment became the city's most viral video of the pre-TikTok era.
^Schrafft, Nichole (July 22, 2025)."Don't worry, they're OK!".Good Morning Gloucester.Archived from the original on 2025-09-18. Retrieved2025-09-17.Joey and Katelyn narrowly escaped the jaws of a scary Mola Mola (sunfish…or "baby wheel")
^Caldwell, David K.; Brown, David H. (January–March 1964)."Notes on killer whales".Bulletin of the Southern California Academy of Sciences.63 (3). Los Angeles, California: Southern California Academy of Sciences: 137.
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