The Zig-Zag Eel (Mastacembelus armatus), also known as the Tire-Track Eel, Tire-Track Spiny Eel or Marbled Spiny Eel, is a species of ray-finned, spiny eels belonging to the genus Mastacembelus of the family Mastacembelidae, and is native to the riverine fauna of India, Bangladesh, Pakistan, Sri Lanka, Thailand, Vietnam, Indonesia and other parts of South-East Asia. Other common names for this popular aquarium species are Leopard Spiny Eel and White-Spotted Spiny Eel. This species is not only a popular aquarium fish but also a food fish in its country of origin.
Mastacembelus armatus is a large elongated fish that has a snake-like body without pelvic fins. Its anal and dorsal fins are elongated and are connected to the caudal fin. The dorsal fin is preceded by numerous spines. The back is dark beige in colour while the head is silver-beige. The body’s colour is dull brown and the belly is a lighter shade of brown. The body may also be marked with brown circular patterns. The body also has one to three darker longitudinal zigzag lines that connect to form a distinct reticulated pattern that is restricted to the dorsal two-thirds of the body. The eyes have brown stripes running laterally through them.
Mastacembelus armatus can reach up to 91 cm in its natural habitat but does not usually exceed 51 cm in captivity.
Mastacembelus armatus are nocturnal fish that thrive in highland streams, lowland wetlands, still waters, coastal marshes and rivers with sandy or rocky riverbeds and heavy vegetation. They are common during the tropical summer months and will dwell in canals, lakes and other floodplain areas during the season.
The tank should be well-planted with floating plants also used. An abundance of hiding places should be provided as this species likes to hide away during the day. Bogwood, rock caves and PVC piping are all suitable for this purpose. Sand should be used as substrate as the Spiny Eels often like to bury themselves. Dimmer lighting will encourage the fish to venture from its hiding places more often. A close-fitting hood is required as the eel can find its way through the smallest of gaps. Water flow should be fairly gentle as the fish mainly inhabits areas of still water in the wild. This species does best when kept in mildly brackish water.
Prefers meaty foods such as prawn, krill, and lancefish. Live and frozen foods can also be fed, however, these foods alone are unlikely to be enough to sustain larger fish. Some specimens will also accept vegetable matter, although this is fairly rare.
Generally, peaceful community fish, although care should be taken to ensure tankmates are too large to be considered prey as this species do eat live fish in the wild. It is recommended to only keep one fire eel per tank as they may be aggressive to conspecifics. This can sometimes be avoided by keeping the fish in groups of five or more individuals.