Synbranchiformes

Synbranchiformes
	Monopterus albus
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Clade:	Percomorpha
Order:	Synbranchiformes; Berg, 1940
Type species
	Synbranchus marmoratus; Bloch, 1795
Families
	Synbranchidae; Chaudhuriidae; Mastacembelidae; Indostomidae

Synbranchiformes, often called

superorder Acanthopterygii

.

Taxonomy

No synbrachiform fossil is known. The Mastacembeloidei were removed from the Perciformes and added to the Synbranchiformes after a phylogenetic analysis by Johnson and Patterson. These authors consider the Synbranchiformes to be part of a

Pleuronectiformes form a sister clade to the Ovalentaria which has been called the “Carangimorpharia” but in the 5th Edition of Fishes of the World this clade remained unnamed and unranked.^[4]

There are a total of about 99 species divided over 15 genera in three families.

Chaudhuriidae, with four genera and five species, and Mastacembelidae

, with three genera and about 26 species.

Modern studies have placed Indostomus, the sole genus within the family Indostomidae, within the Synbranchiformes.^[5]

Description

These eel-like fishes range in size from 8–48

Anguilliformes). The premaxillae are present as distinct bones and are nonprotrusible.^[3] The gills are poorly developed, and their openings are usually single, small, confluent across the breast, and restricted to the lower half of the body.^[3] Oxygen is absorbed through the membranes of the throat or intestine. The dorsal and anal fins are low and continuous around the tail tip. Pelvic fins are absent.^[3]

Scales are either absent or very small. They lack a swim bladder.

Distribution

These fishes are distributed in tropical America, tropical Africa, southeastern and eastern Asia, East Indies, and Australia. The three families each have a somewhat different distribution: The Synbranchidae are found in Mexico, Central and South America, West Africa (Liberia), Asia, Hawaii, and the Indo-Australian Archipelago.^[3] The Mastacembelidae are found in Africa and through Syria to Maritime Southeast Asia, China, and Korea.^[3] The Chaudhuriidae are found in northeastern India through Thailand to Korea (including parts of Malaysia and Borneo).^[3]

Habitat

All except three species occur in

O. infernale from Mexico.^[6] One species, O. bengalense

, commonly occurs in coastal areas of southeastern Asia.

Ecology

Some species are considered air-breathing fishes because of their ability to breathe by highly vascularized buccopharyngeal pouches (pharynx modified for breathing air). They usually are active only at night.

They feed on benthic invertebrates, especially larvae, and fishes.

At least some of the species of the family Synbranchidae, that is, O. infernale, are sexually dimorphic. Adult males grow a head hump, and males are larger than females. These fishes lay about 40 spherical eggs per clutch. The eggs measure between 0.05 and 0.06 in (1.2–1.5 mm) in diameter and have a pair of long filaments for adhesion to the substrate. Reproduction takes place during the wet season, which lasts for several months, during which females probably spawn more than once. Data acquired from studying juvenile growth and the length of representative individuals within a population suggests that they are a short-lived species that matures during the first year, with few individuals surviving to the second breeding season.

Importance to humans

In some parts of Asia, swamp eels and one species of spiny eel,

Mastacembelus erythrotaenia, are valued as food and sometimes are kept in ponds or rice fields. Except for a few mastacembelids, they are rarely seen in home aquaria

. The fish have numerous sharp dorsal spines and belly thorns which, together with its sliminess make them extremely difficult to handle. The spines must be cut off with scissors before consumption.

Tyre track eel

caught in River Tlawng, Mizoram, India 2012

Sources

Books

Baensch, Hans A.; Riehl, Rüdiger (1985). Aquarien Atlas [Aquarium Atlas] (in German). Vol. 2. Melle, West Germany: Verlag für Naturund Heimtierkunde.
Chan, S.T.H.; Tang, F.; Lofts, B. (1973). "The role of sex steroids on natural sex reversal in Monopterus albus". In Scow, Robert O. (ed.). Proceedings of the International Congress of Endocrinology. International Congress of Endocrinology. New York, NY: American Elsevier.
Rainboth, Walter J. (1996). Fishes of the Cambodian Mekong. FAO Species Identification Field Guide for Fishery Purposes. Rome, IT: FAO.
Romero, Aldemaro, ed. (2001). The Biology of Hypogean Fishes. Dordrecht: Kluwer.

Periodicals

Humphreys, W.F. (1999). "The distribution of Australian cave fishes". Records of the Western Australian Museum. 19: 469–472.

Humphreys, W.F.; Feinberg, M.N. (1995). "Food of the blind cave fishes of northwestern Australia". Records of the Western Australian Museum. 17: 29–33.

Johnson, G.D.; Patterson, C. (1993). "Percomorph phylogeny: A survey of Acanthomorphs and a new proposal". Bulletin of Marine Science. 52 (1): 554–626.

Kerle, R.; Britz, R.; Ng, P.K.L. (2000). "Habitat preference, reproduction, and diet of the earthworm eel, Chendol keelini (Teleostei: Chaudhuriidae), a rare freshwater fish from Sundaic southeast Asia". Environmental Biology of Fishes. 57 (4): 413–422.
S2CID 21964814
.

lo Nostro, F.L.; Guerrero, G.A. (1996). "Presence of primary and secondary males in a population of the protogynous Synbranchus marmoratus (Bloch, 1795), a protogynous fish (Teleost, Synbranchiformes)". Journal of Fish Biology. 49: 788–800.

Roberts, T.R. (1986). "Systematic review of the Mastacembelidae or spiny eels of Burma and Thailand, with description of two new species of Macrognathus". Japanese Journal of Ichthyology. 33 (2): 95–109.
S2CID 89096162
.

Sadovy, Y.; Shapiro, D.Y. (1987). "Criteria for the diagnosis of hermaphroditism in fishes". Copeia. 1987 (1): 136–156.
JSTOR 1446046
.

Sanchez, S.; Fenocchio, A. (1996). "Karyotypic analysis in three populations of the South-American eel-like fish Synbranchus marmoratus". Caryologia. 49 (1): 65–71.
doi:10.1080/00087114.1996.10797351
.