The swamp eels (also written "swamp-eels") are a family (Synbranchidae) of freshwater eel-like fishes of the tropics and subtropics. Most species are able to breathe air and typically live in marshes, ponds and damp places, sometimes burying themselves in the mud if the water source dries up. They have various adaptations to suit this lifestyle; they are long and slender, they lack pectoral and pelvic fins, and their dorsal and anal fins are vestigial, making them limbless vertebrates. They lack scales and a swimbladder, and their gills open on the throat in a slit or pore. Oxygen can be absorbed through the lining of the mouth and pharynx, which is rich in blood vessels and acts as a "lung".

Although adult swamp eels have virtually no fins, the larvae have large pectoral fins which they use to fan water over their bodies, thus ensuring gas exchange before their adult breathing apparatus develops. When about two weeks old they shed these fins and assume the adult form. Most species of swamp eel are hermaphrodite, starting life as females and later changing to males, though some individuals start life as males and do not change sex.

In the Jiangnan region of China, swamp eels are eaten as a delicacy, usually cooked as part of a stir-fry or casserole.

It is known as Kusia (কুচিয়া) in Assam and Bangladesh. It is considered a delicacy and cooked with curry as part of Assamese cuisine.

Description

The marbled swamp eel, Synbranchus marmoratus, has been recorded at up to in length,

Most of the species can breathe air, allowing them to survive in low-oxygenated water, and to migrate overland between ponds on wet nights. The linings of the mouth and pharynx are highly vascularised, acting as primitive but efficient lungs. Although swamp eels are not themselves related to amphibians, this lifestyle may well resemble those of the fish from which the land animals evolved during the Devonian period.

  • genus Macrotrema <small>Regan, 1912</small>
  • genus Ophichthys <small>Swainson, 1839</small>
  • genus Ophisternon <small>McClelland, 1844</small>
  • genus Synbranchus <small>Bloch, 1795</small>
  • genus Monopterus <small>Lacepède, 1800</small>
  • genus Rakthamichthys <small>Britz, Dahanukar, Standing, Philip, Kumar & Raghavan, 2020</small>
  • genus Typhlosynbranchus <small>Pellegrin, 1922</small>

In cooking

256px|thumb|right|Fried swamp eel, usually eaten with spicy gravy, one of the most popular dishes in [[Minangkabau cuisine, Indonesia]]

In Indonesia swamp eel is called belut, and are commonly harvested from water ponds of rice paddies and become the protein source for rural population in Indonesia. Swamp eel is usually stir fried served with sambal hot chili sauce as belut penyet, curried, or deep fried to achieve crispy texture as kripik belut.

In the Jiangnan region of China, swamp eels are a delicacy, usually cooked in stirfries or casseroles. The recipe usually calls for garlic, scallions, bamboo shoots, rice wine, sugar, starch, and soy sauce with prodigious amounts of vegetable oil. It is popular in the region from Shanghai to Nanjing. The Chinese name in pinyin of this dish is . The name of the swamp eel is ' or '.

In Assam swamp eels are considered a delicacy and prepared as curry or dry fry. It is believed there that these are good source of iron and good for blood deficiency.

Conservation status

As of 2021, eleven species were listed by the IUCN as species of special concern: Typhlosynbranchus boueti (Liberian swamp eel), Rakthamichthys indicus (Malabar swamp eel), Rakthamichthys roseni, Rakthamichthys digressus, and Ophichthys hodgarti have been classified as data deficient, meaning that they require more study to determine their conservation status. Ophichthys indicus (Bombay swamp eel) is classified as vulnerable. Ophichthys fossorius (Malabar swampeel), Ophisternon infernale (blind swamp eel), Ophisternon candidum (the blind cave eel), and Ophisternon afrum (Guinea swamp eel) are classified as endangered. Ophichthys desilvai (Desilvai's blind eel) is classified as critically endangered.

On the other side of the endangerment issue, invasive Asian swamp eels in Florida are a major threat to populations of crayfish and some other small species.

References

  • FishBase info for Synbranchidae