Ocean sunfish

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The ocean sunfish (Mola mola) is the most massive bony fish in the world. It is a unique pelagic fish, and specimens of ocean sunfish have been observed up to 3.3 m (11 ft) in length and weighing up to 2,300 kg (5,100 lb)."[Mola mola]." FishBase. Ed. Ranier Froese and Daniel Pauly. March 2006 version. N.p.: FishBase, 2006.

A member of order Tetraodontiformes, the ocean sunfish has many derived characters and is the type species of its genus.

The ocean sunfish feeds on jellies and other gelatinous, soft bodied zooplankton, as well as small fish and other marine life.

Contents

1 Physiology

1.1 Fin
1.2 Toxin
1.3 Diet

2 Behavior
3 Environmental Adaptations
4 Range
5 Conservation Notes
6 Name
7 References
8 External links

Physiology

Ocean sunfish.

The ocean sunfish is described as a flat, oval fish with grooves on its body. It has a rounded 'tail' known as a clavus instead of a caudal fin. The short, broad clavus is formed by extensions of dorsal and anal fin rays. It is wavy, with eight to nine ossicles and 12 fin rays. The ocean sunfish has rough, sandpapery skin covered with mucus. Its average weight is one ton and its average length from the tip of the snout to the tip of its clavus is 6 ft (1.8 m). Vertically, from fin to fin, its average size is 11 ft (3.3 m).^{[[Citing sources citation needed]]} The ocean sunfish is taller than it is long and has large, high dorsal and anal fins, which are dark in color. Its tiny mouth cannot be closed and its top and bottom teeth are fused to form a beak. It has a round, bulging eye, and its skin is extremely thick and elastic. There is a distinct line at the posterior where denticles, scales,on the skin change from extremely rough to very fine. Its pectoral fins are small, fan-shaped, and pointed up. It has four gills and a slit behind the last one is covered by a thin flap of skin near the pectoral fin called an operculum.

Because of its very short and stiff body, it has no more than 16 vertebra, and the spinal cord is under 15 mm long (less than 0.5 in). A specimen of 200 kg may have a brain no bigger than a nut. The fish's unusual shape results from its unique development, in which the tail, present in the tiny larva, does not grow with the rest of the body. As the rest of the body grows to the enormous adult size, it 'wraps around' where the tail would normally be, giving the squared, 'cut-off' shape of the adult Mola tail.

Juveniles are silvery in color and adults are usually dark gray to white, with variations in mottling and spots. Sunfish are usually gray above, silvery gray to brown on the side, and paler or dusky below; some individuals are brown. It is able to change color rapidly from spotty to even-colored.

Though unrelated, ocean sunfish are commonly mistaken for sharks, as they often swim close to the surface and have dorsal fins that protrude from the water, reminiscent of the dorsal fins of sharks. They are found in warm and temperate zones of all oceans, including the eastern Pacific and the eastern and western Atlantic. There are three to five species of Mola.

Fin

Like the triggerfishes and pufferfishes it is related to, Mola mola uses its long, thin dorsal and anal fins for propulsion; it lacks a caudal fin (or 'tail fin'), having in its place a rudder-like structure, the clavus. Its fry resemble miniature pufferfish, having spines, a hint at the species's place in the evolutionary tree. The ocean sunfish uses its dorsal and anal fins to "scull." This behavior is described as a way to propel the fish, allowing it to swim forward by moving its dorsal and anal fins from side to side.

Toxin

While the flesh of the Ocean Sunfish is considered a delicacy by some, it contains neurotoxins similar to those of other poisonous tetraodontiformes.

Diet

Sunfish eat jellyfishes, salps, comb jellies, zooplankton, squid, and crustaceans. They live in the Eastern Pacific and Atlantic. Despite the soft and watery nature of their food, it is densely packed with proteins, vitamins and minerals, and occurs in vast swarms. This, and the Mola's huge appetite, is why Molas can grow larger than any other bony fish. Their predators are orcas, sea lions, dolphins and marlin. Molas can produce more than 300 million eggs, each about 2 to 3 mm large, more than any other known vertebrate. They are thought to live for over 10 years. Interestingly, the rough and leathery skin (a fibrous tissue up to 1.5 cm thick) of the Ocean Sunfish is host to more dermal parasites than that of any other marine creature.

Behavior

Sunfish are generally thought to be a solitary fish, swimming freely in the ocean alone. However, certain sightings of molas in groups of more than tens have been reported. Juvenile schools of Sunfish are said to socialize and gather.

Sometimes the molas are spotted floating sideways on the sea surface. Although most scientists are still puzzled at this behavior, it is commonly thought that they are basking in the sun, not sick or unhealthy. Some observers have seen sea birds such as gulls picking ectoparasites off basking sunfish which is another plausible explanation for why the Mola would float on the surface. Some observers have seen the Mola flip over onto its other side after the gull has picked off its parasites, giving the bird a chance to have more food to eat, and the Mola a chance to have the bugs picked off of its body. Breaching has also been observed. This is when sunfish jump out of the water as whales would. They are reported to jump up to ten feet out of the water. This is probably done to dislodge the large number of parasites on their body. Molas also seek drifting kelp in search of small fish to feed off of its abundant parasites.

Environmental Adaptations

The sunfish uses its clavus as a rudder and may also steer with its ability to spit strong jets of water out of its mouth or gills. It sculls and is propelled by waving its dorsal and anal fins from side to side and is a weak swimmer. It usually lets the current carry it. The water supports its enormous weight and its great size gives it safety. Its thick, leathery hide also protects it because it is made up of collagen fibers up to 6 inches thick. It often protects it from the stinging jellyfish, which it eats. Its top and bottom teeth are fused together to form a beak and it also has claw-like teeth in its throat, which are used to help it break up its food before it eats it. The function of its operculum is to keep parasites out of its body. It has a mouth that is perfect for slurping jellies and salps. It is lighter on the bottom of its body and darker above to camouflage better. The Sunfish's very unique ability to suck AND spit water with its mouth helps it while feeding. The Mola sometimes spits jets of water in the sand to search for food. It also sucks and spits jellies to tear them apart and make them easier to consume with its small mouth. The Sunfish has also reportedly used its ability to spit water out of its gills to squirt sea birds, which sometimes land on the Mola's side while it is basking.

Range

Up to 1,800 feet (549 m) in temperate and tropical waters worldwide. They stay in primarily open waters, but are often viewed near kelp beds.

Conservation Notes

Ocean sunfish are sometimes caught accidentally in drift gillnet fisheries. They make up nearly 30% of the total catch of the California drift gillnet fishery for swordfish, outnumbering the amount of swordfish caught. Most sunfish are released alive, but many of the released fish show obvious signs of trauma, including abrasions, bleeding and gill discoloration from air exposure. Reducing bycatch of non-target species is becoming a priority in fisheries management.

Another threat to ocean sunfish are floating plastic bags which look like their natural prey, jellyfish. Sunfish can choke as they try to swallow the bags, or slowly starve as the plastic clogs their stomach. You can help save these animals just by picking up plastic bags at the beach and making sure trash is disposed of properly.

Name

The Ocean Sunfish is also known as the marine sunfish, pez luna, the moon fish, or simply by its specific name, mola (Latin for "millstone", which it was said to resemble because of its gray color, rough texture, and round shape). It has various obsolete binomial synonyms; its original name was Tetraodon mola.

The freshwater sunfishes (family Centrarchidae) are unrelated; for other fishes known as "sunfish", see Sunfish.

References

External links

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