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Asian Swamp Eel
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Species at a Glance
The Asian swamp eel, also called the rice eel, is a member of the swamp-eel family, Synbranchidae. With the help of specialized gills, it has the ability to breathe atmospheric oxygen, allowing it to live in shallow, deoxygenated waters. In addition, the Asian swamp eel can reverse its sex, with most maturing as females and some changing to males over time.
This elongate, snake-like, and cylindrical fish typically has no scales, and no pectoral or pelvic fins. Dorsal, caudal, and anal fins are reduced to folds of skin without fin rays. The head is relatively short and the teeth are small and not easily seen. Eyes are small and covered by a layer of skin. The gill openings form a “V”-shape on the lower throat area. The body and head are dark olive or brown in color above, becoming lighter (often a light orange) below. Some individuals are brightly colored with yellow, black, and gold spots over a light tan, or almost white background. The skin produces a thick mucus layer making the eel difficult to hold. It may grow as long as 0.9-1 m (3-4 ft) and weigh as much as 1 lb.
The Asian swamp eel is most often confused with the American eel (Anguilla rostrata), as well as some species of lamprey. The American eel can be distinguished by the presence of pectoral fins, which are absent in the Asian swamp eel. Lampreys are best identified by seven small pore-like gill openings. This species may also be confused with other invasive swamp-eels such as M. cuchia which is similar to M. albus in appearance, habitat, and behavior; however, M. cuchia has small scales that are absent in M. albus.
Ideal habitat for the Asian swamp eel is tropical and temperate climates with slowly moving freshwater systems such as agricultural areas, wetlands, muddy ponds, canals, swamps, and rice fields. It is nocturnal and will often burrow into soft, moist sediments where it can survive in low oxygen waters and can even gulp air to survive without water for an extended period.
While it’s unclear exactly how the Asian swamp eel was introduced, it was most likely released or escaped from aquariums, fish farms, or through the live fish food market. Because it can breathe air, it may have the ability to move across land, although no occurrences of overland travel have been documented.
Native to tropical and temperate parts of Southeast Asia, the Asian swamp eel was first brought to Hawaii around 1900. Current populations are established in Hawaii, Georgia, Florida, and New Jersey. In 2014, Asian swamp eels were found in Maryland; however, they are not currently established.
Note: Distribution data for this species may have changed since the publication of the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016), the source of information for this description.
This species has characteristics that make it very adaptable to new environments. It currently has no known predators in North America; therefore, it has the potential to grow and spread quickly and become widespread in the United States. Because they are a generalized predator, the Asian swamp eel is a potential threat to native fishes, frogs, and aquatic invertebrates.
Information for this species profile comes from the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016).