Ocean sunfish

From Wikipedia, the free encyclopedia

Ocean sunfish
Conservation status
Secure
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Actinopterygii Order: Tetraodontiformes Family: Molidae Genus: Mola Species: M. mola
Binomial name
Mola mola (Linnaeus, 1758)

The ocean sunfish, Mola mola, is the largest 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).^[1]

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

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

Contents 1 Physiology 1.1 Fins 1.2 Toxins 1.3 Diet 1.4 Reproduction 1.5 Life 2 Behavior 3 Environmental adaptation 4 Range 5 Sightings 6 Conservation notes 7 Name 8 Notes 9 References 10 External links

[edit] Physiology

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).^{[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 round, bulging eyes, 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 upwards. 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 25 mm long (less than 1 in).^[2] A specimen of 200 kg may have a brain no bigger than a nut.^{[citation needed]} The fish's unusual shape results from its unique development, in which the tail 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.^{[citation needed]}

Juveniles are silvery in color and adults are usually dark gray to white, with variations in mottling and spots. Ocean sunfish are usually grey above, silvery grey 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, similar to 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.

[edit] Fins

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 which provide a hint at the species' 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. The mode of swimming utilized by the Mola mola can be described as Tetradontiform, in which they use oscillations of their dorsal and anal fins to propel themselves through the water.

[edit] Toxins

While the flesh of the ocean sunfish is considered a delicacy by some, it contains neurotoxins similar to those of other poisonous tetraodontiformes.^[1]

[edit] Diet

Ocean 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 the reason why molas can grow larger than any other bony fish. Their predators while smaller are orcas, Sea Lions, dolphins and marlin. Orcas are the only likely predators of large adults.

[edit] Reproduction

Molas can produce more than 300 million eggs, each about 2 to 3 mm in diameter, more than any other known vertebrate.^[1]

[edit] Life

They are thought to live for over 10 years. Interestingly, the rough and leathery skin (a fibrous tissue up to 15 mm thick) of the ocean sunfish is host to more dermal parasites than that of any other marine creature.^{[citation needed]}

[edit] Behavior

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

Sometimes 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 ocean sunfish which is another plausible explanation why the mola would float on the surface. Some observers have seen mola flip over onto its other side after the gull has picked off its parasites, giving the bird a chance to have more food, and the mola a chance to have the bugs picked off of its body. Breaching has also been observed. This is when ocean 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.^[3] Molas also seek drifting kelp in search of small fish to remove their abundant parasites.^[4]

[edit] Environmental adaptation

The ocean 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.^{[citation needed]} Its skin often protects it from the stinging jellyfish that it eats. Its top and bottom teeth are fused 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 reaches its stomach. 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. Like most fish, it is lighter colored on the bottom of its body and darker above for better camouflage. The ocean sunfish's 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 ocean 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.^{[citation needed]}

[edit] Range

Depths of 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.

[edit] Sightings

The sighting by scientists of 19 ocean sunfish in a two hour period off the south-west tip of Cornwall in July 2006 has been cited as evidence of the increased temperature of British waters.^[5]

An ocean sunfish was also sighted by Mr Richard Harrison and Mr Jim Harrison aboard their private craft off Port Eynon Headland on the Gower Peninsula in Wales on the 26th August 2006. The fish was swimming within 1/2 a mile of the shore with its dorsal fin protruding from the surface. Upon further investigation the ocean sunfish was approximately 4feet long and looked to be alone.

A dead ocean sunfish was sighted floating in the River Tay, Scotland in the vicinity of Broughty Ferry on Saturday 2nd September 2006 by members of the Tay Sail Training Association and 5 members of the Ralfs Family. The ocean sunfish was approximately 1 to 1.5 metres long.

A 'basking' ocean sunfish was spotted near Port Quin, Wadebridge, Cornwall UK on Monday 25th September 2006 by John Willacy whilst sea kayaking below cliffs.^[6]

A dead ocean sunfish measuring 3.3 m long and 3.2 m high was collected off the coast of Whangarei, New Zealand in November 2006. It is believed to be the largest sunfish ever found with a weight of around 2.2 - 2.3 tonnes.^[7]

One specimen of sunfish was seen on Sunday, 25^th February 2007 of the coast of Zamboanga, Philippines. Measuring 2.3 meters long, 1.3 meters wide and weighing one tonne. The giant sunfish appeared to be weak while it was beaching off the coast, however it died on the same day. Local marine biologists have stated that due to its weakness it could have been washed ashore. An on-going necropsy is being carried out to determine the cause of death.^[8]

Recently, A group of students in a computer lab watching Monteray Bay aquatic web cam were graced with seeing two of these amazing rare fish within almost immediate vicinity. Unknown if those at the aquatic institute were aware of this occurrence.

In March 2007, two Macquarie University academics sighted and photographed a 1.5 tonne sunfish near Jervis Bay on the New South Wales south coast in Australia. They initially believed the sunfish was a shark.^[9]

[edit] 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, outweighing the number 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. People can help protect these animals by picking up plastic bags at the beach and properly disposing of trash.

[edit] 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 grey 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.

[edit] Notes

[edit] References

• ITIS Mola mola
• FishBase
• [1]

[edit] External links

• Fishbase.org-mola mola
• Video Of Divers And A Ocean Sunfish
• Ocean sunfish research and information, Tierney Thys, PhD
• Ocean sunfish photographs, Mike Johnson Marine Natural History Photography
• Ocean sunfish photographs, Phillip Colla Photography
• Ocean sunfish photographs, Jens Kuhfs Photography
• Ocean sunfish, Mola mola, natural history photographs
• Picture of huge mola, size comparison to a swimmer
• Larval ocean sunfish
• 1,200 lb Mola mola
• People with mola
• Mola close-up
• Sunfish skeletal structure
• The different Molidae species
• Molidae photo and video gallery from Bali