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Anguilla marmorata, known by many common names including the marbled eel, giant mottled eel and long finned eel, is one of about 19 species in its genus, the only genus in the small freshwater eel family Anguillidae. Of the angillid eels, the marbled eel has the widest distribution, found in several discrete but intermixing populations throughout the tropics and subtropics across the southwestern and central Pacific ocean, in the northwestern Pacific as far north as Japan, and in the southeastern Indian ocean to southern Africa (Wanatabe et al. 2008, 2009; Gagnaire et al. 2011). It has been recorded in small numbers from the Galapagos (McCosker et al. 2003) though whether this is the edge of their natural range or an introduction is unclear (Vishwanath and Mailautoka 2012).
Marbled eels, like other anguillid eels, have a complex life history, spending most of their life in the “yellow eel growth phase,” during which they inhabit the bottoms of fresh and brackish continental waters. This can last 2-3 years in warmer regions and up to 20 years in colder northern areas. The eels then migrate long distances as “silver eels” to spawning regions in open ocean gullies located at depths of 150-300 meters (500-1540 feet). The spawning areas for the different marbled eel populations are not well identified, although those in the northern pacific are known to share spawning areas in the Mariana trench with the Japanese eel Anguilla marmorata (Tsukamoto 2011). The planktonic larvae hatch at sea and develop into glass eel larvae to return to continental waters. There they metamorphose into the pigmented elver stage whereupon they begin to feed and travel in schools to freshwater inland rivers, lakes, streams and estuaries where they complete their development. In areas of large shallow coastal seas, they may stay as elvers without migrating upstream to fresh waters (Vishwanath and Mailautoka 2012).
Distinguished by their mottled brown, green and yellow coloration, adults reach up to 2 meters (6.6 feet) in length; one of the largest angillids. They are usually encased in slime making them very slippery. Nocturnal carnivores, the adult eels eat a diverse diet rich in fish, amphibians and invertebrates such as crab and shrimp (Froese and Pauly 2006). Like other anguillid eels, the marbled eel is a sought-after commercial food fish, eaten at many of its developmental stages, and its fishery may well expand as other species of angillids decline (especially A. anguilla and A. japonica). Currently it is listed by the IUCN as of least concern at it is common throughout its wide range, however its potential vulnerability to decline due to fisheries pressure and habitat loss is recognized as an important parameter to monitor (Vishwanath and Mailautoka 2012).