Swamp eel
Encyclopedia
The swamp eels are a family
(Synbranchidae) of freshwater
eel
-like fish
es of the worldwide tropics.
, Monopterus indicus, reaches no more than 8.5 centimetres (3.3 in).
Swamp eels are almost entirely finless; the pectoral and pelvic fins are absent, the dorsal
and anal fins are vestigial, reduced to rayless ridges, and the caudal fin ranges from small to absent, depending on species. Almost all of the species lack scale
s. The eyes are small, and in some cave-dwelling species they are beneath the skin, so that the fish is blind. The gill
membranes are fused, and the gill opening is either a slit or pore underneath the throat. The swim bladder and ribs are also absent. These are all believed to be adaptations for burrowing into soft mud during periods of drought, and swamp eels are found in the mud underneath a dried-up pond.
Most of the species can breathe air, allowing them to survive in deoxygenated 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 amphibian
s, this lifestyle may well resemble those of the fish from which the land animals evolved during the Devonian
period.
Although the adults are virtually finless, the larvae are born with greatly enlarged pectoral fins. The fins are used to propel streams of oxygenated water from the surface along the larva's body. The skin of the larva is thin and vascularised, allowing it to extract oxygen from this stream of water. As the fish grows, the adult air-breathing organ begins to develop, and it no longer requires the fins. At the age of about two weeks, the larvae suddenly sheds the pectoral fins, and takes on the adult form.
Most species are protogynous hermaphrodites; that is, most individuals begin life as females, but later change into males. This typically occurs at around four years of age, although a small number of individuals are born male and remain so throughout their life.
Family Synbranchidae
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
(Synbranchidae) of freshwater
Freshwater
Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...
eel
Eel
Eels are an order of fish, which consists of four suborders, 20 families, 111 genera and approximately 800 species. Most eels are predators...
-like fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
es of the worldwide tropics.
Description
The marbled swamp eel, Synbranchus marmoratus, has been recorded at up to 150 centimetres (59.1 in) in length, while the Bombay swamp eelMonopterus indicus
Monopterus indicus is a species of fish in the Synbranchidae family. It is endemic to India.-Source:*Dahanukar, N. 2011. . In: IUCN 2011. . Version 2011.2. Downloaded on 27 November 2011....
, Monopterus indicus, reaches no more than 8.5 centimetres (3.3 in).
Swamp eels are almost entirely finless; the pectoral and pelvic fins are absent, the dorsal
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
and anal fins are vestigial, reduced to rayless ridges, and the caudal fin ranges from small to absent, depending on species. Almost all of the species lack scale
Scale (zoology)
In most biological nomenclature, a scale is a small rigid plate that grows out of an animal's skin to provide protection. In lepidopteran species, scales are plates on the surface of the insect wing, and provide coloration...
s. The eyes are small, and in some cave-dwelling species they are beneath the skin, so that the fish is blind. The gill
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
membranes are fused, and the gill opening is either a slit or pore underneath the throat. The swim bladder and ribs are also absent. These are all believed to be adaptations for burrowing into soft mud during periods of drought, and swamp eels are found in the mud underneath a dried-up pond.
Most of the species can breathe air, allowing them to survive in deoxygenated water, and to migrate overland between ponds on wet nights. The linings of the mouth and pharynx
Pharynx
The human pharynx is the part of the throat situated immediately posterior to the mouth and nasal cavity, and anterior to the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx , the oropharynx , and the laryngopharynx...
are highly vascularised, acting as primitive but efficient lungs. Although swamp eels are not themselves related to amphibian
Amphibian
Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...
s, this lifestyle may well resemble those of the fish from which the land animals evolved during the Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
period.
Although the adults are virtually finless, the larvae are born with greatly enlarged pectoral fins. The fins are used to propel streams of oxygenated water from the surface along the larva's body. The skin of the larva is thin and vascularised, allowing it to extract oxygen from this stream of water. As the fish grows, the adult air-breathing organ begins to develop, and it no longer requires the fins. At the age of about two weeks, the larvae suddenly sheds the pectoral fins, and takes on the adult form.
Most species are protogynous hermaphrodites; that is, most individuals begin life as females, but later change into males. This typically occurs at around four years of age, although a small number of individuals are born male and remain so throughout their life.
In cooking
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 called chao shan hu. The name of the swamp eel is shan yu.Classification
The family includes twenty-two currently recognized species in four genera.Family Synbranchidae
- Genus Macrotrema Regan, 1912
- Macrotrema caligans (CantorTheodore Edward CantorTheodore Edward Cantor was a Danish physician, zoologist and botanist.Cantor worked for the British East India Company. He made natural history collections in Penang and Malacca...
, 1849)
- Macrotrema caligans (Cantor
- Genus MonopterusMonopterusMonopterus is a genus of fish in the Synbranchidae family.- Species :* Monopterus albus — Swamp eel, Rice eel, White ricefield eel* Monopterus boueti — Liberian swamp eel...
ernard Germain de Lacépède|Lacépède, 1800- Asian Swamp EelMonopterus albusMonopterus albus is an important air-breathing commercial species of fish in the Synbranchidae family...
, Monopterus albus (Zuiew, 1793) - Monopterus bicolor Nguyen & Nguyen, 2005
- Liberian Swamp Eel, Monopterus boueti (PellegrinJacques PellegrinJacques Pellegrin was a French zoologist.Pellegrin was born in Paris, and studied natural history. In 1894 he became assistant chairman of zoology at the Muséum national d'histoire naturelle, replacing Léon Vaillant .He got his doctorates in medicine and science...
, 1922) - Cuchia, Monopterus cuchia (HamiltonFrancis HamiltonFrancis Hamilton may refer to:*Francis Buchanan-Hamilton, later known as Francis Hamilton, Scottish physician*Francis Alvin George Hamilton, Canadian politician usually known as Alvin Hamilton*Sir Francis Hamilton, 1st Baronet...
, 1822) - Monopterus desilvai Bailey & Gans, 1998
- Monopterus dienbienensis Nguyen & Nguyen, 2005
- Monopterus digressus Gopi, 2002
- Monopterus eapeni Talwar, 1991
- Malabar Swamp Eel, Monopterus fossorius (Nayar, 1951)
- Indian Spaghetti-eel, Monopterus hodgarti (Chaudhuri, 1913)
- Bombay SwampeelMonopterus indicusMonopterus indicus is a species of fish in the Synbranchidae family. It is endemic to India.-Source:*Dahanukar, N. 2011. . In: IUCN 2011. . Version 2011.2. Downloaded on 27 November 2011....
, Monopterus indicus (Silas & Dawson, 1961) - Monopterus roseni Bailey & Gans, 1998
- Asian Swamp Eel
- Genus OphisternonOphisternonOphisternon is a genus of fish in the Synbranchidae family.It contains the following species:* Obscure swamp eel * Guinea swamp eel * Bengal eel...
McClelland, 1844- Obscure Swamp Eel, Ophisternon aenigmaticum Rosen & Greenwood, 1976
- Guinea Swamp Eel, Ophisternon afrum (BoulengerGeorge Albert BoulengerGeorge Albert Boulenger FRS was a Belgian-British zoologist who identified over 2000 new animal species, chiefly fish, reptiles and amphibians.-Life:...
, 1909) - Bengal Eel, Ophisternon bengalense McClelland, 1844
- Blind Cave EelBlind cave eelThe Blind Cave eel is a species of fish in the Synbranchidae family. It is endemic to caves and groundwater in Australia.-Sources:* Wager, R. 1996. . Downloaded 4 August 2007....
, Ophisternon candidum (MeesGerlof Fokko MeesDr Gerlof Fokko Mees is a Dutch ichthyologist, ornithologist and museum curator who was born in the Netherlands, grew up in the Dutch East Indies, and spent much of his life working in Australasia...
, 1962) - Australian Swamp Eel, Ophisternon gutturale (RichardsonJohn Richardson (naturalist)Sir John Richardson was a Scottish naval surgeon, naturalist and arctic explorer.Richardson was born at Dumfries. He studied medicine at Edinburgh University, and became a surgeon in the navy in 1807. He traveled with John Franklin in search of the Northwest Passage on the Coppermine Expedition of...
, 1845) - Blind Swamp Eel, Ophisternon infernale (HubbsCarl Leavitt Hubbs-Youth:He was born in Williams, Arizona. He was the son of Charles Leavitt and Elizabeth Hubbs. His father had a wide variety of jobs . The family moved several times before settling in San Diego where he got his first taste of natural history...
, 1938)
- Genus Synbranchus BlochMarcus Elieser BlochMarcus Elieser Bloch was a German medical doctor and naturalist. He is generally considered one of the most important ichthyologists of the 18th century.- Life :...
, 1795- Synbranchus lampreia Favorito, Zanata & Assumpção, 2005
- Synbranchus madeirae Rosen & Rumney, 1972
- Marbled Swamp Eel, Synbranchus marmoratus BlochMarcus Elieser BlochMarcus Elieser Bloch was a German medical doctor and naturalist. He is generally considered one of the most important ichthyologists of the 18th century.- Life :...
, 1795