Moray eel

Moray eel
Temporal range: Late Miocene–Recent

[1]

Picture of a moray eel taken in the Maldives in 2006
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Superorder: Elopomorpha
Order: Anguilliformes
Family: Muraenidae
Rafinesque, 1810
Genera

See text.

Moray eels or Muraenidae are a family of cosmopolitan eels. The approximately 200 species in 15 genera are almost exclusively marine, but several species are regularly seen in brackish water, and a few, for example the freshwater moray (Gymnothorax polyuranodon), can sometimes be found in fresh water.[2]

The smallest moray is likely Snyder's moray (Anarchias leucurus), which attains a maximum length of 11.5 cm (4.5 in),[3] while the longest species, the slender giant moray (Strophidon sathete) reaches up to 4 m (13 ft).[4] The largest in terms of total mass is the giant moray (Gymnothorax javanicus), which reaches 3 m (9.8 ft) in length and 30 kg (66 lb) in weight.[5]

Anatomy

Photo of undulating moray on top of a coral colony
Muraena helena showing typical moray eel morphology: robust anguilliform shape, lack of pectoral fins and circular gill openings

The dorsal fin extends from just behind the head along the back and joins seamlessly with the caudal and anal fins. Most species lack pectoral and pelvic fins, adding to their serpentine appearance. Their eyes are rather small; morays rely on their highly developed sense of smell, lying in wait to ambush prey.

The body is generally patterned. In some species, the inside of the mouth is also patterned. Their jaws are wide, framing a protruding snout. Most possess large teeth used to tear flesh or grasp slippery prey items. A relatively small number of species, for example the snowflake moray (Echidna nebulosa) and zebra moray (Gymnomuraena zebra), primarily feed on crustaceans and other hard-shelled animals, and they have blunt, molar-like teeth suitable for crushing.[6]

Two diagrams of head and spine, one showing the pharyngeal jaw at rest; the other showing the jaws extended into the mouth
Moray eel jaw anatomy

Moray eels' heads are too narrow to create the low pressure most fishes use to swallow prey. However, they have a second set of jaws in their throat called pharyngeal jaws, which also possess teeth (like tilapia). When feeding, morays launch these jaws into the mouth, where they grasp prey and transport it into the throat and digestive system. Moray eels are the only animals that use pharyngeal jaws to actively capture and restrain prey.[7][8][9]

Morays secrete a protective mucus over their smooth, scaleless skin, which in some species contains a toxin. They have much thicker skin and high densities of goblet cells in the epidermis that allows mucus to be produced at a higher rate than in other eel species. This allows sand granules to adhere to the sides of their burrows in sand-dwelling morays,[10] thus making the walls of the burrow more permanent due to the glycosylation of mucins in mucus. Their small, circular gills, located on the flanks far posterior to the mouth, require the moray to maintain a gap to facilitate respiration.

Morays are carnivorous and feed primarily on smaller fish, octopuses, squid, cuttlefish, and crustaceans. Groupers, barracudas and sea snakes are among their few predators. Commercial fisheries exist for several species, but some cause ciguatera fish poisoning.

Behavior

Cooperative hunting

Photo of eel with shrimp in its mouth
A Pacific cleaner shrimp cleans the mouth of a moray eel

Reef-associated roving coralgroupers (Plectropomus pessuliferus) have been observed to recruit giant morays to join them in hunting for food. The invitation to hunt is initiated by head-shaking. The rationale for this joining of forces is the ability of the morays to enter narrow crevices and flush prey from niches not accessible to groupers. This is the only known instance of interspecies cooperative hunting among fish. Cooperation on other levels, such as at cleaning stations, is well known.[11][12]

Photo of eel in coral with wide open mouth
Fimbriated moray,
Gymnothorax fimbriatus

Reputation

Morays are frequently thought of as particularly vicious or ill-tempered animals. In truth, morays hide from humans in crevices and would rather flee than fight. They are shy and secretive, and attack humans only in self defense or mistaken identity. Most attacks stem from disruption of a moray's burrow (to which they do react strongly), but an increasing number also occur during hand feeding of morays by divers, an activity often used by dive companies to attract tourists. Morays have poor vision and rely mostly on their acute sense of smell, making distinguishing between fingers and held food difficult; numerous divers have lost fingers while attempting hand feedings, so the hand feeding of moray eels has been banned in some locations, including the Great Barrier Reef. The moray's rear-hooked teeth and primitive but strong bite mechanism also makes bites on humans more severe, as the eel cannot release its grip, even in death, and must be manually pried off. While the majority are not believed to be venomous, circumstantial evidence suggests a few species may be.[6]

Eels that have eaten certain types of toxic algae, or more frequently that have eaten fish that have eaten some of these algae, can cause ciguatera fish poisoning if eaten. Ciguatera fish poisoning is very dangerous and can kill.

Habitat

Moray eels at the Shedd Aquarium

Moray eels are cosmopolitan, found in both tropical and temperate seas, although the largest species richness is at reefs in warm oceans. Very few species occur outside the tropics or subtropics, and the ones that do only extend marginally beyond these regions. They live at depths to several hundred metres, where they spend most of their time concealed inside crevices and alcoves. While several species regularly are found in brackish water, very few species can be found in fresh water, for example, the freshwater moray (Gymnothorax polyuranodon) and the pink-lipped moray eel (Echidna rhodochilus).[13]

Taxonomy

Genera

Whitemouth moray, Gymnothorax meleagris
Gymnothorax javanicus, very common in the tropical Indo-Pacific, is one of the biggest species, able to reach 3m long and weight 70kg

There are currently around 202 known species of moray eels, divided between 16 genera. The genus Gymnothorax is by far the broadest, including more than half of the total number of species.

List of genera according to the World Register of Marine Species :

References

  1. ↑ Froese, Rainer, and Daniel Pauly, eds. (2009). "Muraenidae" in FishBase. January 2009 version.
  2. ↑ Froese, Rainer and Pauly, Daniel, eds. (2010). "Gymnothorax polyuranodon" in FishBase. January 2010 version.
  3. ↑ Froese, Rainer and Pauly, Daniel, eds. (2010). "Anarchias leucurus" in FishBase. January 2010 version.
  4. ↑ Froese, Rainer and Pauly, Daniel, eds. (2010). "Strophidon sathete" in FishBase. January 2010 version.
  5. ↑ Froese, Rainer and Pauly, Daniel, eds. (2012). "Gymnothorax javanicus" in FishBase. May 2012 version.
  6. 1 2 Randall, J. E. (2005). Reef and Shore Fishes of the South Pacific. University of Hawai'i Press. ISBN 0-8248-2698-1
  7. ↑ Mehtal, Rita S.; Peter C. Wainwright (2007-09-06). "Raptorial jaws in the throat help moray eels swallow large prey". Nature. 449 (7158): 79–82. doi:10.1038/nature06062. PMID 17805293. Retrieved 2007-09-06.
  8. ↑ Hopkin, Michael (2007-09-05). "Eels imitate alien: Fearsome fish have protruding jaws in their throats to grab prey.". Nature News. doi:10.1038/news070903-11. Retrieved 2007-09-06.
  9. ↑ National Science Foundation (Sep. 5, 2007)
  10. ↑ Fishelson L (September 1996). "Skin morphology and cytology in marine eels adapted to different lifestyles". Anat. Rec. 246 (1): 15–29. doi:10.1002/(SICI)1097-0185(199609)246:1<15::AID-AR3>3.0.CO;2-E. PMID 8876820.
  11. ↑ In the December 2006 issue of the journal Public Library of Science Biology, a team of biologists announced the discovery of interspecies cooperative hunting involving morays. The biologists, who were engaged in a study of Red Sea cleaner fish (fish that enter the mouths of other fish to rid them of parasites), made the discovery.An Amazing First: Two Species Cooperate to Hunt | LiveScience
  12. ↑ Bshary R, Hohner A, Ait-el-Djoudi K, Fricke H (December 2006). "Interspecific communicative and coordinated hunting between groupers and giant moray eels in the Red Sea". PLoS Biol. 4 (12): e431. doi:10.1371/journal.pbio.0040431. PMC 1750927Freely accessible. PMID 17147471.
  13. ↑ Tsukamoto, Watanabe, Kuroki, Aoyama, and Miller (2014). Freshwater habitat use by a moray eel species, Gymnothorax polyuranodon, in Fiji shown by otolith microchemistry. Environmental Biology of Fishes 97(12): 1377-1385.

External links

Wikimedia Commons has media related to Muraenidae.
Wikisource has the text of the 1905 New International Encyclopedia article Moray.
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