Ocean Sunfish

Ocean Sunfish, Mola mola

The Ocean Sunfish, Mola mola, whose common Spanish name is mola, is a member of the Molas or Molidae Family, known collectively as molas in Mexico. This fish received its common name from its habit of lying on its side on the water surface to take in rays. The Molidae Family has only four fish placed in three genera. There are only two global members of the genus Mola, both are found in Mexican waters, one in the Pacific and one in both the Atlantic and the Pacific.

The Ocean Sunfish have truncated strongly compressed bullet-shaped bodies and a long oval appearance when seen head-on. Their body depth is 70 to 72% of standard length; when their anal and dorsal fins are extended, they are about as deep as they are long. They range in color from brown to silvery-gray or white with a variety of mottled skin patterns; they are darker dorsally than ventrally. They have the ability to camouflage themselves by changing colors when under attack. Their head has a very small terminal mouth that cannot be fully closed and four fused beak-like teeth similar to those of the parrotfish or pufferfish. Their extended anal fin has a short base and no spines but has 14 to 17 rays. Similarly, their extended dorsal fin has a short base and no spines but has 15 to 18 rays. Their caudal fin is unique as it never evolved; it is a small rudder-like structure called a clavus that has 12 rays and terminates in a rounded ossicle. Their pectoral fins are small and rounded. They do not have scales but have very thick rough textured skin that can be as thick as 7.3 cm (2.9 inches) and numerous denticles. They are covered with mucus.

The Oceanic Sunfish are a pelagic species found globally in all tropical and temperate seas. They are ginormous fish reaching 4.4 meters (14 feet) in length and 2,268 kg (5,000 pounds) in weight, with females being larger than males. They can be found from the surface to depths up to 2,000 feet in waters that are warmer than 10oC (50oF). They move with the oceanic currents being awkward and clumsy slow swimmers. They are known to lie on their sides on the water surface which is believed to “thermally recharge” their body temperature following dives into deeper and colder water. They travel as single individuals, in pairs or in large schools. They are considered omnivores with nutritionally poor diets, consuming primarily large amounts of jellyfish and much smaller amounts of algae, small fish, and zooplankton. In turn they are preyed upon by Orca Whales, Sea Lions, and larger sharks; juveniles are known to be preyed upon by Bluefin Tuna and Dolphinfish. They are plagued with heavy infestations of more than 40 internal and skin parasites, thus they frequent areas near kelp beds in nutrient-rich waters to access smaller fish which will remove ectoparasites from their skin. Their habit of lying on their sides on the water surface also allows sea birds to remove parasites. They are known to breach to heights of 3.3 meters (10 feet) which is believed to be a third method to try to remove skin parasites. Their reproduction cycle is poorly understood but is believed to be oviparous with females producing up to 300,000 eggs per year that are released and externally fertilized by males. Newly hatched Ocean Sunfish larvae are only 2.5 mm (0.098 inches) long and weigh a fraction of a gram. Juveniles resemble pufferfish having large pectoral fins, a tail fin, and body spines that are not present in adult sunfish. Juveniles travel in schools for protection, but become more solitary as they mature. Their lifespan in the wild is unknown, however, they have been maintained for up to 10 years in captivity. They are a poorly studied species and little is known about their behavioral patterns. The Mola mola is scientifically interesting as its spinal column contains fewer vertebrae and is shorter in relation to the body than that of any other fish; it is the heaviest known bony fish in the world. Each female has the ability to produce 300,000 eggs, more than any other known vertebrate, and the larvae have the potential to grow to more than 60 million times their birth size (the most extreme size growth of any vertebrate animal).

The Ocean Sunfish are a pelagic species found globally in all tropical and temperate seas. New sightings off the coast of southwest England are generating additional support for increasing marine temperatures. In Mexican waters they are found throughout the Gulf of Mexico with the exception that they are absent from along the east coast of the Yucatán; in the Pacific they have a limited distribution being found along the entire west coast of Baja and throughout the Sea of Cortez.

The Ocean Sunfish is easy to identify, however, in the wild it can be confused with various sharks because it travels with its dorsal fin protruding above the ocean surface.

The Ocean Sunfish are a frequent by-catch in drift gill nets, with high mortality rates, and are principally taken by the swordfish fishery. They also consume ocean trash such as plastic bags causing them to suffocate. They are unregulated worldwide; some fishermen consider them pests and will “fin” them before releasing them resulting in eventual death. Reports vary on their value for human consumption. In Asia they are considered a delicacy. In Europe they are banned from sale. Unsubstantiated reports indicate that their internal organs contain neurotoxins and tetrodotoxin. We do not recommend the human consumption of this fish. Some parts of the fish are also reported to be used in Chinese medicine. They are considered harmless to humans but are curious and will approach divers. In some parts of the world they are the focus fish of commercial dive trips. They are not widely held in aquarium exhibits, due to the unique and demanding requirements of their care. The Monterey Bay Aquarium has had success in raising fish in captivity but these get very large very quickly (increasing size by 14 times in one year) and are eventually returned to the ocean. Due to their size, slow swimming abilities, and travel in large schools, they are a known hazard to boating navigation.

Ocean Sunfish (1)

Ocean Sunfish, Mola mola. Fish caught from coastal waters off Santa Rosalita, Baja California, August 2011. Length: 41 cm (16 inches). Catch and photos courtesy of Barry Mastro. Note that the large dorsal fin is not visible and is concealed by the body – it is plainly obvious in the submitted a video of this catch which is available in the public domain: https://www.youtube.com/watch?feature=player_detailpage&v=XU1kaGE1jt8. Impressive!

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f544-ocean-sunfish-4Ocean Sunfish, Mola mola. Sun bathing fin caught on camera in coastal waters off Long Beach, California, May 2016. Photos courtesy of Ben Cantrell, Peoria, IL.

Ocean Sunfish, Mola mola. Underwater photo taken in coastal waters off San Diego, CA, October 2014. Length: 1.27 meters (5 feet 0 inches). Photo courtesy of Bob Hillis, Ivins, UT.