Mastacembelus erythrotaenia

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The Mastacembelus erythrotaenia, also called Fire Eel, is a large freshwater spiny eel from Southeast Asia, valued for its dramatic shape and orange-red markings. Despite its snake-like appearance, it is a true fish belonging to the Mastacembelidae. This species requires a very spacious aquarium, a safe layout and a suitable feeding routine. Its adult size, burrowing habits and preference for hiding make it a choice for prepared aquarists. With a rarity rating of 2, the Mastacembelus erythrotaenia is less commonly available than many popular community fish. Its crepuscular behavior adds interest, but it also means that daytime activity can be limited.

General species description

The Mastacembelus erythrotaenia is a freshwater eel-shaped fish with an elongated body covered in small scales. A series of low dorsal spines runs along its back, a defining feature of spiny eels, while the snout is elongated and mobile. Usually discreet during daylight, it becomes more active at dusk and during the night. It spends part of its time buried in the substrate or hidden beneath roots. In an aquarium, it may learn to recognize its keeper without becoming constantly visible. Its growth and adult size require **an aquarium of several hundred litres at minimum**, with a tightly fitted cover. This is a **relatively uncommon fish in the trade**, corresponding here to rarity level 2.

Geographical origin and habitat

This species is native to Southeast Asia, including several mainland and island drainage systems. In Indonesia, it is associated with **Sumatra, Java and Borneo**, while its range also includes areas of the Malay Peninsula and the Mekong basin. It inhabits slow to moderately flowing waters, often carrying suspended particles, where banks, roots and debris provide numerous shelters. The bottom is generally made up of **fine sand, mud or soft gravel**, allowing the fish to bury itself. Riparian vegetation provides shade and helps stabilize the banks. In an aquarium, roots, smooth pipes and sturdy plants reproduce this habitat more safely than sharp rockwork.

Precise location and local name

In Indonesia, the Mastacembelus erythrotaenia is known by the vernacular name **belut api**, literally meaning “fire eel” and referring to its red markings. It occurs in various waterways and floodplain habitats across **Sumatra, Java and Borneo**, rather than being restricted to one exact site. Local names may vary between regions, as is common for widely distributed fish. The English name Fire Eel is widely used in the international aquarium trade. Fish from different areas may vary in colour intensity, but they should be kept according to the same general principles: clean water, abundant shelters and careful escape prevention.

Appearance and physical characteristics

The body of the Mastacembelus erythrotaenia is long, cylindrical and strongly compressed toward the rear. Its base colour ranges from dark brown to blackish grey, with **orange-red lines and spots** especially visible along the flanks and rear body. The head is pointed, the eyes are relatively small and the snout has short tactile projections that help it explore the bottom. The dorsal, caudal and anal fins merge around the rear of the body, creating a continuous outline. Juveniles often show sharper contrasts than adults. Maximum length may approach **100 cm**, although aquarium size depends greatly on available space, feeding and maintenance quality.

General diet

The Mastacembelus erythrotaenia is primarily carnivorous and searches for food along the bottom, particularly as light levels fall. In nature, its diet includes worms, aquatic larvae, small crustaceans and other benthic prey. In an aquarium, it generally accepts meaty foods such as clean earthworms, shrimp, mussels, krill and sinking pellets for carnivorous fish. It is best fed **at dusk**, using portions appropriate for its size. Newly imported specimens may refuse dry foods and need a gradual transition. A varied, controlled diet helps prevent obesity while supporting healthy growth. Small fish or invertebrates that can fit into its mouth may be eaten, so tank mates must be chosen with care.

Essential data

• Name of native river: Mekong and Chao Phraya drainage systems
• Local name: Belut api
• Origin of the scientific name: Greek-based genus name and descriptive species epithet
• Full-name etymology: Mastacembelus refers to a snout shaped like a proboscis or wedge; erythrotaenia means “red bands”
• Common and vernacular names: Fire Eel, fire eel, belut api
• Family: Mastacembelidae
• Subfamily: Mastacembelinae
• Name pronunciation: mas-tass-EM-beh-luss - eh-rith-roh-TAY-nee-ah
• Discovery: Pieter Bleeker, 1850
• Maximum adult size: Approximately 100 cm
• Water temperature and pH: 24 to 28 °C; pH 6.5 to 7.5
• Stream appearance and surrounding vegetation: Slow to moderate water, shaded banks, roots, leaf litter and dense vegetation
• Typical tank mates: Chromobotia macracanthus, Barbonymus schwanenfeldii, Pangio semicincta, Kryptopterus bicirrhis
• Temperament and behaviour: Generally peaceful and secretive, with burrowing habits and peak activity at dusk and night
• Water depth: Shallow to moderately deep water, close to the bottom and shelter
• Sexual dimorphism: Difficult to identify; mature females may be more robust
• Bottom structure and flow: Sand, mud or fine gravel; slow to moderate current

In your aquarium

Success with the Mastacembelus erythrotaenia begins with a very large, well-filtered aquarium fitted with a cover that has no gaps. Provide a **soft substrate**, several shelters and subdued lighting, then feed the fish after the lights gradually go out. Avoid sharp rocks and tank mates small enough to be swallowed. Stable water, regular water changes and patient acclimation are essential. Its eventual size and longevity make this fish unsuitable for small aquariums, even when purchased as a juvenile.