#synbranchiformes

[herpsandbirds]

Fire Eel (Mastacembelus erythrotaenia), family Mastacembelidae, order Synbranchiformes, found in freshwater habitats in SE Asia

This species is not a “true eel”, but is in a group called the spiny eels.

photographs by Stan Sung

[uncharismatic-fauna]

Uncharismatic Fact of the Day

Think all eels live in water? Think again! In 2018 scientists described a new species of swamp eel which they believe resides almost entirely on land. The eel, dubbed Rakthamichthys rongsaw, is bright pink and has extremely tiny, almost non-functional eyes; a result of its subterranean lifestyle depriving it of the need for sight or pigment. Only one individual has been found in north-east India, so the extent of its distribution is currently unknown.

(Image: The only known specimin of Rakthamichthys rongsaw by Rachunliu G Kamei)

[bestanimal]

Round 3 - Actinopterygii - Synbranchiformes

(Sources - 1, 2, 3, 4)

Order: Synbranchiformes

Common Name: “swamp eels”

Families: 4 - Synbranchidae (“swamp eels”), Chaudhuriidae (“earthworm eels”), Mastacembelidae (“spiny eels”), and Indostomidae (“armoured sticklebacks”)

Anatomy: long, eel-like body; poorly developed gills with small openings; dorsal and anal fins are low and continuous around the tail tip; no pelvic fins; no or very small scales; no swim bladder

Diet: crustaceans, worms, amphibians, small fish, turtle eggs

Habitat: tropical parts of America and Africa, southeastern and eastern Asia, East Indies, and Australia; most species live in swamps, caves, and sluggish fresh and/or brackish waters

Evolved in: possibly Late Cretaceous, but no synbrachiform fossils are known

Do you have a favorite in Synbranchiformes?

One or more of my favorite animals is in Synbranchiformes

I love at least one or more of these animals

I like at least one or more of these animals

I am neutral about all of these animals

I dislike all of these animals

Voting ended onAug 1, 2025

Propaganda under the cut:

Swamp eels (family Synbranchidae) (image 2) are capable of traveling on land, and some can live out of water for extended periods of time. The linings of their mouth and pharynx are highly vascularised, acting as primitive but efficient lungs. Some species are burrowers, burying themselves in mud if their water source dries up, or even spending their entire lives underground.

Most species of swamp eel are hermaphrodites, starting life as females and later changing to males. This typically occurs around four years of age, although a small number of individuals are born male and remain so throughout their lives.

Some species of swamp eel live exclusively in caves, and, like many other cavefish, have lost their eyes and pigment. The endangered Blind Cave Eel (Ophisternon candidum) is the longest cavefish in Australia (up to 40 cm [16 in]) and one of the only three vertebrates in Australia that is restricted to underground waters.

Male Swamp Eels take the responsibility of building a nest or burrow, and guarding over their eggs.

All known species of Earthworm Eels (family Chaudhuriidae) (image 2) are the size and shape of earthworms. They have no scales and their eyes are small, covered in thick skin.

The Sri Lanka Five-eyed Spiny Eel (Macrognathus pentophthalmos) was described as a common species as recently as 1980, but has since suffered a rapid decline. There have been no recent confirmed sightings, and the fish is classified as “critically endangered, possibly extinct”. It is not known what caused the population to crash so suddenly.

Some spiny eels exist in the aquarium trade and are commonly kept as pets, including the Peacock Eel (Macrognathus siamensis) (see gif above), Fire Eel (Mastacembelus erythrotaenia) (image 1), and Zig-zag Eel (Mastacembelus armatus). They are relatively peaceful, though they hunt smaller fish, and require soft substrate to burrow in. In their native range, these fish are also caught for food.

The genus Indostomus (image 4) were long thought to be sticklebacks (suborder Gasterosteoidei, within the order Perciformes), but more modern analyses have found them to be in this order instead. Unlike their eel-like relatives, they have armored skin and fan-shaped tails.

[taxonomytournament]

Taxonomy Tournament: Fish

Synbranchiformes. This order is made up swamp eels, which are eel-like but have spiny rays in their fins.

Gobiiformes. This order is made up of gobies, some of the smallest fish there are.

Which clade of animals is better?

Synbranchiformes

Gobiiformes

Show results

Voting ended onFeb 8, 2024

[herpsandbirds]

Fire Eel (Mastacembelus erythrotaenia), family Mastacembelidae, order Synbranchiformes, found in freshwater habitats in SE Asia

This species is not a “true eel”, but is in a group called the spiny eels.

photograph by Stan Sung

[herpsandbirds]

Asian Swamp Eel aka Rice Paddy Eel (Monopterus albus), family Synbranchidae, order Synbranchiformes, found in East and SE Asia

photos: Seah TM, Hyun-tae Kim, & Karolina Tomaszek

[uncharismatic-fauna]

Uncharismatic Fact of the Day

Swamp eels get the best of both worlds in just about everything! They feed readily on animals, plants, and carrion. They have gills to breathe in water, and thanks to the high number of blood vessels present in the mouth and throat, most species are also able to breathe air, and can even move across land to find new bodies of water. Lastly, many species are also protogynus, beginning their lives as female and transitioning to male as they get older.

(Image: An Asian swamp eel (Monopterus albus) by Hyun-tae Kim)

[herpsandbirds]

Spiny Eels, family Mastacembelidae, order Synbranchiformes, found in fresh water environments in SE Asia

L - Black Pearly Eel (Mastacembelus notophthalmus) R - Panther Eel (Mastacembelus pantherinus)

photograph by Stan Sung