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.
Known Predators:
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).
Range mass: 2235 (high) kg.
Range length: 3.1 (high) m.
Other Physical Features: ectothermic ; bilateral symmetry
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).
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
Aquatic Biomes: pelagic
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 ); atlantic ocean (Native ); pacific ocean (Native ); mediterranean sea (Native )
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).
Little is known regarding methods of communication and perception of ocean sunfish.
Perception Channels: tactile ; chemical
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).
US Federal List: no special status
CITES: no special status
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).
Ocean sunfish are often caught as bycatch in commercial fishing nets, which can be a great inconvenience (Liu et al., 2009).
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 ; body parts are source of valuable material
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
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).
Animal Foods: fish; mollusks; aquatic crustaceans; cnidarians; zooplankton
Plant Foods: macroalgae
Primary Diet: herbivore (Algivore); planktivore
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).
Range number of offspring: 300,000,000 (high) .
Little is known regarding parental investment of offspring in ocean sunfish.
The Ocean Sunfish or Mola (Mola mola) is the world's heaviest bony fish. The distinctive body shape is laterally compressed and appears bluntly terminated to the rear, as if the tail had been lopped off. Molas have a reduced skeleton, with fewer vertebrae than any other fish. Metamorphosis from larva to adult is remarkable in that, unlike most fish, Molas pass through two distinct larval phases—a typical Tetraodon pufferfish-like larval and another highly transformative stage resulting in the complete absorption of the tail (Fraser-Brunner 1951). Molas have been claimed to be the most fecund vertebrates known, with a single female reportedly producing several hundred million eggs at once (Schmidt 1921, cited in Pope et al. 2010).
Molas have a very broad global distribution, occurring in both temperate and tropical waters of the Atlantic, Indian, and Pacific Oceans. Due to their primarily pelagic (open water) distribution, studying their ecology and behavior is challenging. They are most easily observed basking at the surface, a behavior for which several functions have been proposed, including warming themselves after deep dives into cold water and presenting themselves to seabirds and other fishes that remove parasites (such as Pennella copepods) from their bodies (Abe et al. 2012; Pope et al. 2010 and references therein). Although Molas were long believed to be sluggish swimmers, drifting passively in ocean currents, based on investigations in recent years (e.g., Cartamil and Lowe 2004; Sims et al. 2009; Dewar et al. 2010) it is now clear that Molas do not necessarily travel with prevailing currents and instead appear to be relatively active predators that are capable of migrating at least moderate distances, perhaps in response to shifts in regional productivity and temperature. Gelatinous zooplankton (such as jellyfishes, salps, and pyrosomes) comprise a large fraction of the diet of these fish, although Syväranta et al. (2012) have used stable isotype analyses to argue that the extent of dependence of Molas on gelatinous zooplankton may be overstated, as was suggested by Pope et al. (2010) (but see Logan and Dodge 2013 and Harrod et al. 2013). Stable isotope studies of Molas in the Mediterranean Sea by Cardona et al. (2012) supported the assertion that gelatinous zooplankton are at least a major component of the diet. Hays et al. (2009) compared foraging depths for Molas and Leatherback Turtles (Dermochelys coriacea)--the heaviest bony fish and the heaviest sea turtle, both of which are believed to feed heavily on gelatinous zooplankton. They found that while Molas can feed from the surface to depths greater than 500 m, Leatherbacks are limited to relatively shallow waters (<200 m), presumably because of the constraint that they must return to the surface to breathe air.
Although Molas are caught and sold in only a few parts of the world, such as Japan and Taiwan, in recent years they have been taken incidentally in substantial numbers in many fisheries, including the swordfish drift gillnet fishery off California and Oregon (U.S.A.), the illegal Spanish driftnet swordfish fishery off the Gibraltar Straits in the Mediterranean, and the the tuna and swordfish longline fishery off the coast of South Africa (Dewar et al. 2010 and references therein).
The taxonomic treatment of fishes in the family Molidae has fluctuated considerably through time. Current molecular, morphological, and distributional data appear to support the recognition of at least two species in the genus Mola: M. mola and the far less familiar M. ramsayi (which is likely limited to the southern hemisphere), as well as possibly at least one more. Because of the unresolved taxonomic issues in the genus Mola, it is possible that some studies supposedly done on M. mola may actually apply to a different closely related species. Two additional species are included in the family Molidae, Masturus lanceolatus and Ranzania laevis. The Molidae are closely related to the Tetraodontidae (pufferfishes) and Diodontidae (porcupine fishes). (Bass et al. 2005; Yoshita et al. 2009; Pope et al. 2010 and references therein)
Pope et al. (2010) provide a wide-ranging and thorough review of the limited available data on the taxonomy, morphology, ecology, and conservation of Molas. The oceansunfish.org website is a rich source of information about molas.
(Bass et al. 2005 and references therein; Pope et al. 2010 and references therein)
Sims et al. (2009) used a fast-acquisition global positioning system (Fastloc GPS) tag with remote data retrieval to track long-term movements of three Ocean Sunfish (Mola mola) captured and tagged off southern Portugal. This allowed tracking in near real time with position accuracy of <70 m. These fish are known to dive to depths of at least 472 m and can often remain at deep depths for long periods, only returning occasionally, and then often only briefly, to the surface. The system implemented permitted reception and transmission of location information whenever the fish came close to the surface.
According to Sims et al., their study represents the first demonstration of long-term (>90 days) GPS tracking of a large pelagic fish and shows the great potential for this technique, whereby GPS-quality location data are retrieved remotely via conventional Argos satellites. By freeing researchers from the restriction of working on estuarine or nearshore species in order to physically recover tags to download GPS acquisition data, this technique offers tremendous potential for tracking large pelagic fish species that surface relatively frequently. Although the high spatial accuracy of this technique for fish in open ocean habitats has practical applications for both fisheries and conservation, it will not be suitable for fish species that remain in deep water after tagging.
In the early part of the 20th Century, Ocean Sunfish were sometimes described as active swimmers, but in other cases described as sluggish, inefficient swimmers, passively carried by ocean currents. Modern tracking studies of these fish using attached acoustic transmitters, acceleration dataloggers, and satellite-linked archival transmitters have demonstrated that they are active swimmers both horizontally and vertically. Sims et al. (2009) found that the Ocean Sunfish they tracked covered around 10 to 20 km per day, a rate that is comparable to the movements of pelagic sharks. GPS track integration with current direction/strength maps showed individuals often headed into and across prevailing currents associated with mesoscale eddies. These data confirm that Ocean Sunfish are not passive drifters, but rather, are in fact active swimmers with movement rates within the range observed for other pelagic fishes. Search-like movements occurred over at least three distinct spatial scales. At fine scales, Ocean Sunfish spent longer in highly localised areas with faster, straighter excursions between them. These "stopovers" during long-distance movement appear consistent with finding and exploiting food patches.
Sims et al. (2009) suggest that there would be great value in pursuing long-term GPS tracking of other large pelagic fish species--such as tunas, billfish, and sharks--that surface relatively frequently and have high conservation priority in many ocean regions where a greater understanding of when and why they use certain habitats could enhance management.
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.[4] Adults typically weigh between 247 and 1,000 kg (545 and 2,205 lb). The species 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.
Sunfish are generalist predators that consume largely small fish, fish larvae, squid, and crustaceans. Sea jellies and salps, 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 than any other known vertebrate,[5] up to 300,000,000 at a time.[6] 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 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.[7] Sunfish are frequently caught in gillnets.
A member of the order Tetraodontiformes, which also includes pufferfish, porcupinefish, and filefish, the sunfish shares many traits common to members of this order. The ocean sunfish, Mola mola, is the type species of the genus.
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 翻車魚; fān chē yú, meaning "toppled wheel fish". The ocean sunfish has various superseded binomial synonyms, and was originally classified in the pufferfish genus, as Tetraodon mola.[8][9] It is now placed in its own genus, Mola, with three species: Mola mola, Mola tecta and Mola alexandrini (previously known as Mola ramsayi). The ocean sunfish, Mola mola, is the type species of the genus.[10]
The genus Mola belongs to the family Molidae. This family comprises three genera: Masturus, 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, which is unrelated to Molidae. On the other hand, the name "ocean sunfish" and "mola" refer only to the family Molidae.[5]
The family Molidae belongs to the order Tetraodontiformes, 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 (tetra=four, odous=tooth, and forma=shape). Indeed, sunfish fry resemble spiky pufferfish more than they resemble adult molas.[11]
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 3.3 m (10 ft 10 in) in height have been recorded.[12]
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),[5][13][14] but even larger individuals are not unheard of. The maximum size recorded is 3.3 m (10 ft 10 in) in length,[12][15] and maximum weight recorded is 2,300 kg (5,100 lb).[15]
The spinal column of M. mola contains fewer vertebrae and is shorter in relation to the body than that of any other fish.[16] 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.[16][17] Its teeth are fused into a beak-like structure,[18] which prevents them from being able to fully close their mouths, while also having pharyngeal teeth located in the throat.[19]
The sunfish lacks a swim bladder.[16] Some sources indicate the internal organs contain a concentrated neurotoxin, tetrodotoxin, like the organs of other poisonous tetraodontiformes,[18] while others dispute this claim.[20]
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,[21][22] and is used by the fish as a rudder.[23] The smooth-denticled clavus retains 12 fin rays and terminates in a number of rounded ossicles.[24]
Ocean sunfish often swim near the surface, and their protruding dorsal fins are sometimes mistaken for those of sharks.[25] 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.[26]
Adult sunfish range from brown to silvery-grey or white, with a variety of region-specific mottled skin patterns.[5] 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.[5] 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 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.[16]
More than 40 species of parasites may reside on the skin and internally, motivating the fish to seek relief in a number of ways.[5][24] One of the most frequent ocean sunfish parasites is the flatworm Accacoelium contortum.[27]
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 3 m (10 ft), in an apparent effort to dislodge embedded parasites.[25][28]
Ocean sunfish are native to the temperate and tropical waters of every ocean in the world.[16] Mola genotypes appear to vary widely between the Atlantic and Pacific, but genetic differences between individuals in the Northern and Southern hemispheres are minimal.[29]
Although early research suggested sunfish moved around mainly by drifting with ocean currents, individuals have been recorded swimming 26 km (16 mi) in a day at a cruising speed of 3.2 km/h (1.7 kn).[23]
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 200 m (660 ft), occupying both the epipelagic and mesopelagic zones.[30]
Sunfish are most often found in water warmer than 10 °C (50 °F);[30] prolonged periods spent in water at temperatures of 12 °C (54 °F) or lower can lead to disorientation and eventual death.[26] 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.[29][31] 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,[32][33] 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.[34]
Sunfish are usually found alone, but occasionally in pairs.[16]
The diet of the ocean sunfish was formerly thought to consist primarily of various jellyfish. However, genetic analysis reveals that sunfish are actually generalist predators that consume largely small fish, fish larvae, squid, and crustaceans, with jellyfish and salps making up only around 15% of the diet.[35] 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.[5]
Ocean sunfish may live up to ten years in captivity, but their lifespan in a natural habitat has not yet been determined.[25] Their growth rate remains undetermined. However, a young specimen at the Monterey 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.[26]
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[16] and sea lions.[5][26]
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.[16] Females are estimated to be carrying as many as 300 million eggs, more than any other known vertebrate.[5] Sunfish eggs are released into the water and externally fertilized by sperm.[24]
Newly hatched sunfish larvae are only 2.5 mm (3⁄32 in) 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,[23] arguably the most extreme size growth of any vertebrate animal.[36][37]
Sunfish fry, with large pectoral fins, a tail fin, and body spines uncharacteristic of adult sunfish, resemble miniature pufferfish, their close relatives.[24][38] Young sunfish school for protection, but this behavior is abandoned as they grow.[39]
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.[40]
Despite their size, ocean sunfish are docile and pose no threat to human divers.[24] 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.[41] Areas where they are commonly found are popular destinations for sport dives, and sunfish at some locations have reportedly become familiar with divers.[18] 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,[42] or to the propellers of larger ships, as well as to the fish.[24]
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.[20] Some parts are used in some areas of traditional medicine.[18] 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.[7]
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.[23] The bycatch rate is even higher for the Mediterranean swordfish industry, with 71% to 90% of the total catch being sunfish.[20][39]
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.[43] 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.[25]
Many areas of sunfish biology remain poorly understood, and various research efforts are underway, including aerial surveys of populations,[44] satellite surveillance using pop-off satellite tags,[20][44] genetic analysis of tissue samples,[20] and collection of amateur sighting data.[45] A decrease in sunfish populations may be caused by more frequent bycatch and the increasing popularity of sunfish in human diet.[16]
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.[26] The Kaiyukan Aquarium in Osaka is one of few aquariums with M. mola on display, where it is reportedly as popular an attraction as the larger whale sharks.[46] The Lisbon Oceanarium in Portugal has sunfish showcased in the main tank,[47] and in Spain, the Valencia Oceanogràfic[48] has specimens of sunfish. The Ocean sunfish is also on display at the Denmark Nordsøen Oceanarium.[49]
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 72 cm (2.36 ft) at the time of delivery, but was 187 cm (6.14 ft) in size at the time of death.[50][51]
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,[52] 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,[53] and in 1964 held a 290-kilogram (650 lb) specimen, said to be the largest ever captured at that time.[54] However, another 450-kilogram (1,000 lb) specimen was brought alive to Marineland Studios Aquarium, near St. Augustine, Florida, in 1941.[55]
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.[26] Mola mola has since become a permanent feature of the Open Sea exhibit.[23] Monterey Bay Aquarium's largest sunfish specimen was euthanized on February 14, 2008, after an extended period of poor health.[56]
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.[46] 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.[26] 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).[12]
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,[57] and to take food from the end of a pole or from human hands.[26]
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. Adults typically weigh between 247 and 1,000 kg (545 and 2,205 lb). The species 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.
Sunfish are generalist predators that consume largely small fish, fish larvae, squid, and crustaceans. Sea jellies and salps, 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 than any other known vertebrate, 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 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. Sunfish are frequently caught in gillnets.
A member of the order Tetraodontiformes, which also includes pufferfish, porcupinefish, and filefish, the sunfish shares many traits common to members of this order. The ocean sunfish, Mola mola, is the type species of the genus.