Mola mola
Giant sunfish
(Also: Headfish; Mola ocean sunfish; Moonfish; Ocean Sunfish; Ocean sunfish; Sun-fish; Sunfish)

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). (Ayling and Cox, 1982; Cartamil and Lowe, 2004; Houghton, et al., 2006; Konow, et al., 2006; Liu, et al., 2009; Muus, 1964; Sims and Southall, 2002; Smith, 1965; Wheeler, 1969)

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). (Humann and Deloach, 2002; Hutchins, 2004; Konow, et al., 2006)

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). (Houghton, et al., 2006; Humann and Deloach, 2002; Hutchins, 2004; Linnaeus, 1758; Smith, 1965; Wheeler, 1969)

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). (Ayling and Cox, 1982; Humann and Deloach, 2002; Hutchins, 2004; Smith and Heemstra, 1986)

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). (Bass, et al., 2005; Pope, et al., 2010)

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. (Hutchins, 2004; Muus, 1964)

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). (Bass, et al., 2005; Nakatsubo, et al., 2007; Pope, et al., 2010)

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

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). (Liu, et al., 2009)

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

Little is known regarding the home range of ocean sunfish.

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

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). (Cartamil and Lowe, 2004; Liu, et al., 2009; Wheeler, 1969)

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. (Cartamil and Lowe, 2004)

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). (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). (Humann and Deloach, 2002)

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

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). (Cartamil and Lowe, 2004; Liu, et al., 2009)

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). (Linnaeus, 1758; Smith and Heemstra, 1986)