Monopterus albus

Swamp Eel

Classification

Synbranchidae

Distribution

Very widespread, being found in India, Myanmar, China, Thailand, Cambodia, Laos, Vietnam, Hong Kong, Japan, Taiwan, Malaysia, Indonesia, Philippines, Australia. Has also been introduced to both Hawaii and the USA.

Habitat

Occurs in a variety of habitats, including rivers, ponds, rice paddies, canals, ditches and of course swamps. It can survive in very stagnant and polluted conditions, and during dry spells often burrows into wet earth, where it remains hidden until the rains return.

Maximum Standard Length

40″ (100cm), although the occasional larger specimen has been recorded.

Aquarium SizeTop ↑

72″ X 24″ X 24″ (180cm x 60cm x 60cm) – 680 litres.

Maintenance

Provide the fish with plenty of hiding places. plants, bogwood, rocks and lengths of plastic piping can all be used. The tank absolutely must have an extremely tightly-fitting, heavy cover, as the eel will escape if given the slightest opportunity and could potentially travel a fair distance if it gets loose.

Water Conditions

Temperature: 77-82°F (25-28°C) is recommended, although it's reported to have the ability to withstand freezing conditions. It would certainly appear to be equally happy in cooler waters, as viable populations now exist in parts of the US.

pH: 6.0-8.0

Hardness: 3-25°H

Diet

Feeds on a variety of prey in the wild, including fish, amphibians and invertebrates. In the aquarium it will accept prawns, white fish (such as lancefish) and earthworms.

Behaviour and CompatibilityTop ↑

Best kept singly and alone due to its large adult size and piscivorous nature.

Sexual Dimorphism

No external sexual differences, though once they undergo the transition from female to male (see below), males are said to grow larger.

Reproduction

Has not been spawned in captivity. In nature, spawning occurs in shallow waters, where the fish lay up to 1000 eggs in a loose bubble nest. This is then guarded by the male. It is not a seasonal spawner and breeds all year round. Interestingly, all the fry are initially female, with a percentage changing sex only when maturity is reached. In the event of females being scarce, males also retain the ability to reverse the change!

NotesTop ↑

An incredibly hardy species, M. albus has the ability to travel over land for short distances if kept moist and as mentioned above, often burrows into moist earth (sometimes up to a depth of 1.5 metres!) in order to survive dry conditions. It has only a single gill slit, located on the bottom of the throat, that allows it to trap air in its specially adapted gills. These contain an accessory breathing organ, which takes the form of a pair of lung-like sacs at the rear of the gill chamber. In this way, it can breathe without water for short periods. This fish is not often observed in nature, as it’s an almost exclusively nocturnal species. Its rudimentary eyes are tiny and are covered by a thin epidermic layer.

It is, in fact, not a true eel (order Anguilliformes), as it lacks the twin gill openings and the scales, dorsal, anal, caudal and functioning pectoral fins that characterise Anguilliform species. With swamp eels (order Synbranchiformes), the dorsal, anal and caudal fins are greatly reduced and do not possess any rays. They also don’t have a swimbladder and lack ribs. This latter point probably contributes to its status as a valued food fish in some of its native countries.

In the hobby the swamp eel is not seen very often and obviously is not a fish for the general aquarist, due to its somewhat specific requirements.