The fire eel is not a true eel, but an extremely elongated fish with a distinctive pointed snout and underslung mouth. It is part of a group of fishes called spiny eels that also includes tire track and peacock eels. The group gets its common name from the many small dorsal spines that precede the dorsal fin. The body is laterally compressed, particularly the rear third, where it flattens as it joins the caudal fin and forms an extended tail. The fire eel's base coloring is dark brown/grey, while the belly is generally a lighter shade of the same color. Several bright red lateral stripes and spots mark the body, and vary in intensity depending on the age and condition of the individual. Usually the markings are yellow/amber in juvenile fish, changing to a deep red in larger ones. Often the anal, pectoral, and dorsal fins have a red edging.
The fire eel can grow to a considerable size in the wild with specimens often exceeding 1.2 meters (3.9 ft) in length. However, due to limiting factors in the captive environment they usually reach a maximum of around 55 centimeters (22 in), even in very large aquaria.
Fire eels inhabit river environments with slow to briskly moving water and fine sediment. In the wild they occur across a relatively broad area covering a large part of Southeast Asia including Borneo, India, Malaysia, Myanmar (Burma), Sri Lanka, Sumatra, and Thailand. They are bottom-dwellers that spend large portions of their time buried in the riverbed, often leaving only their snout visible. However, they are voracious predators and when hunting will visit all depths.
- "BioLib - Mastacembelus erythrotaenia". BioLib. Retrieved 24 May 2012.