Moray eels, or Muraenidae (/ˈmɒreɪ,məˈreɪ/), are a familyofeels whose members are found worldwide. There are approximately 200 species in 15 genera which are almost exclusively marine, but several species are regularly seen in brackish water, and a few are found in fresh water.[2]
The English name, from the early 17th century, derives from Portuguesemoréia, which itself derives from Latinmūrēna, in turn from Greekμύραινα, muraina; these are the Latin and Greek names of the Mediterranean moray.[3][4]
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 mostly on their highly developed sense of smell, lying in wait to ambush prey.[5]
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. 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]
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,[7] thus making the walls of the burrow more permanent due to the glycosylationofmucins 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.[clarification needed]
The pharyngeal jaws of morays are located farther back in the head and closely resemble the oral jaws (complete with tiny "teeth"). When feeding, morays launch these jaws into the mouth cavity, where they grasp prey and transport it into the throat. Moray eels are the only known animals that use pharyngeal jaws to actively capture and restrain prey in this way.[8][9][10]
Moray eel jaw anatomy
In addition to the presence of pharyngeal jaws, morays' mouth openings extend far back into the head, compared to fish which feed using suction. In the action of lunging at prey and biting down, water flows out the posterior side of the mouth opening, reducing waves in front of the eel which would otherwise displace prey. Thus, aggressive predation is still possible even with reduced bite times.[11] In at least one species, the California moray (Gymnothorax mordax), teeth in the roof of the mouth are able to fold down as prey slides backwards, thus preventing the teeth from breaking and maintaining a hold on prey as it is transported to the throat.
Differing shapes of the jaw and teeth reflect the respective diets of different species of moray eel. Evolving separately multiple times within the Muraenidae family, short, rounded jaws and molar-like teeth allow durophagous eels (e.g. zebra moray and genus Echidna) to consume crustaceans, while other piscivorous genera of Muraenidae have pointed jaws and longer teeth.[12][13][14] These morphological patterns carry over to teeth positioned on the pharyngeal jaw.[15][16]
Skull and pharyngeal jaws of a Gymnothorax miliaris (goldentail moray)
Reef-associated roving coral groupers (Plectropomus pessuliferus) have been observed recruiting giant morays to help them hunt. The invitation to hunt is initiated by head-shaking. This style of hunting may allow morays to flush prey from niches not accessible to groupers.[22][23][24]
The moray eel can be found in both fresh and saltwater habitats. The vast majority of species are strictly marine, never entering freshwater. Of the few species known to live in freshwater, the most well-known is Gymnothorax polyuranodon.[25][26]
Echidna nebulosa occupying a live coral reef, located in Sabang, Philippines
Although the moray eel can occupy both tropical oceans and temperate oceans, as well as both freshwater and saltwater, the majority of moray eels occupy warm saltwater environments, which contain reefs.[27] Within the tropical oceans and temperate oceans, the moray eel occupies shelters, such as dead patch reefs and coral rubble rocks, and less frequently occupies live coral reefs.[27]
A representative structure of the Uropterygiinae sub-class
There are about 202 known species of moray eels, in 16 genera. These genera are in two sub-families, Muraeninae and Uropterygiinae, which are distinguished by the location of their fins.[28] In Muraeninae the dorsal fin is near the gill slits and runs down the back of the eel, and the anal fin is behind the anus.[28] In the Uropterygiinnae, both the dorsal and the anal fin are at the end of the tail.[28] Though this distinction can be seen between the two sub-families, there are still many varieties of genera within Muraeninae and Uropterygiinae. Of these, the genus Gymnothorax is by far the broadest, including more than half of the total number of species.
The moray eel's elongation is due to an increase in the number of vertebrae, rather than a lengthening of each individual vertebra or a substantial decrease in body depth.[29] Vertebrae have been added asynchronously between the pre-tail ("precaudal") and tail ("caudal") regions, unlike other groups of eels such as Ophicthids and Congrids.[30]
Several moray species are popular among aquarium hobbyists for their hardiness, flexible diets, and disease resistance. The most commonly traded species are the snowflake, zebra and goldentail moray (Gymnothorax miliaris). Several other species are occasionally seen, but are more difficult to obtain and can command a steep price on the market.[31]
Moray eels, particularly the giant moray (Gymnothorax javanicus) and yellow-edged moray (G. flavimarginatus), are known to accumulate high levels of ciguatoxins, unlike other reef fish;[32][33] if consumed by humans, ciguatera fish poisoning may result. Ciguatera is characterised by neurological, gastrointestinal, and cardiovascular problems that may persist for days after eating tainted fish. In morays, the toxins are most concentrated in the liver.[33] In an especially remarkable instance, 57 people in the Northern Mariana Islands were poisoned after eating just the head and half of a cooked yellow-edged moray.[34] Thus, morays are not recommended for human consumption.
^"moray". thefreedictionary.com. Retrieved 11 December 2016.; D'Arcy Wentworth Thompson, Glossary of Greek Fishes (London: Oxford University Press, 1947) pp. 162-165
^Reece JS, Bowen BW, Smith DG, Larson A (November 2010). "Molecular phylogenetics of moray eels (Muraenidae) demonstrates multiple origins of a shell-crushing jaw (Gymnomuraena, Echidna) and multiple colonizations of the Atlantic Ocean". Molecular Phylogenetics and Evolution. 57 (2): 829–35. Bibcode:2010MolPE..57..829R. doi:10.1016/j.ympev.2010.07.013. PMID20674752.
^Mehta RS (January 2009). "Ecomorphology of the moray bite: relationship between dietary extremes and morphological diversity". Physiological and Biochemical Zoology. 82 (1): 90–103. doi:10.1086/594381. PMID19053846. S2CID19640346.
^Collar DC, Reece JS, Alfaro ME, Wainwright PC, Mehta RS (June 2014). "Imperfect morphological convergence: variable changes in cranial structures underlie transitions to durophagy in moray eels". The American Naturalist. 183 (6): E168–84. doi:10.1086/675810. PMID24823828. S2CID17433961.
^Böhlke, Eugenia B., ed. (1989). Fishes of the Western North Atlantic, part 9: Orders Anguilliformes and Saccopharyngiformes. New Haven: Sears Foundation for marine research, Yale University. ISBN978-0935868456. OCLC30092375.
^Gregory, William K. (2002). Fish skulls: a study of the evolution of natural mechanisms. Malabar, Fla.: Krieger Pub. ISBN978-1575242149. OCLC48892721.
^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 Seacleaner 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
^ abTsukamoto, Katsumi; Watanabe, Shun; Kuroki, Mari; Aoyama, Jun; Miller, Michael J. (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. Bibcode:2014EnvBF..97.1377T. doi:10.1007/s10641-014-0228-9. ISSN0378-1909. S2CID7596020.
^Khlentzos, Constantine T. (1950-09-01). "Seventeen Cases of Poisoning Due to Ingestion of an Eel, Gymnothorax Flavimarginatus 1". The American Journal of Tropical Medicine and Hygiene. s1-30 (5): 785–793. doi:10.4269/ajtmh.1950.s1-30.785. ISSN0002-9637. PMID14771403.
