Order : Anguilliformes
Family : ANGUILLIDAE
Species : 19 species
Maximum Length : up to 200 cm (in female Anguilla marmorata)

As of 2022, there are 19 species of freshwater eels recognised by Fishbase, of which 9 or 10 occur in Southeast Asia (see Kottelat, 2013 for taxonomic details).

Within Southeast Asia the most widespread species appears to be the Giant Mottled Eel (Anguilla marmorata), illustrated here. The range of this species extends from East Africa, through the Indian Ocean and Southeast Asia to the western Pacific Ocean, including Japan and French Polynesia.

Other species are limited in their range, for example Anguilla borneensis is endemic to the island of Borneo and Anguilla luzonensis is limited to a small part of the island of Luzon, in the Philippines.

Freshwater eels are catadromous; as adults they live most of their lives in freshwater habitats, but when fully mature they migrate to seas and oceans to breed and subsequently die. Young eels (elvers) then return to rivers, streams, marshes and lakes to complete the cycle.

Freshwater eels are demersal, which means they live close to the bed of seas, rivers, streams and lakes. As a result their presence is often overlooked, especially if there is aquatic plant growth in which to hide. Smaller eels sometimes conceal themselves beneath rocks.

Some species are plain in colour, typically brownish, greenish or yellowish, and others are mottled. Their dorsal, tail and anal fins are merged into a single continuous structure; this feature, and their elongated shape, makes them fast, strong swimmers. They possess soft scales embedded in their smooth skin. 

Their diet can be variable, but it may include small fishes, molluscs and crustaceans. Some species are farmed, most notably the Japanese Eel (Anguilla japonica).
 

Figs 1 and 2 : Giant Mottled Eel (Anguilla marmorata) from Rarotonga, Cook Islands; this species may grow up to 150-200 cm total length.


References :

Kottelat, M., 2013. The fishes of the inland waters of Southeast Asia: a catalogue and core bibliography of the fishes known to occur in freshwaters, mangroves and estuaries. The Raffles Bulletin of Zoology 2013 (Suppl. 27):1-663.


Links :

Fishbase