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Fire Eel
Mastacembelus erythrotaenia
The Fire Eel is a giant Southeast Asian river fish. This massive carnivore requires a tank of at least 1000 liters featuring very fine sand to prevent self-evisceration and large opaque plastic tubes.
- Taxonomy
- Class:ActinopteriOrder:SynbranchiformesFamily:MastacembelidaeGenus:MastacembelusSpecies:Mastacembelus erythrotaenia
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Water Temperature
24 - 28 °C
pH Value
6 - 7.5
Water type
Freshwater
Tank level
Bottom
Adult size
100 cm
Minimum tank volume
>= 500 L
Minimum group
>= 1
GH
5 - 15 dGH
KH
2 - 7 dKH
TDS
95 - 295 ppm
Conductivity
148 - 461 uS/cm
Species description
Geographical Origin and Habitat: Southeast Asia (Thailand, Cambodia, Borneo, Sumatra). Large slow or moderate flowing rivers. Clay and muddy substrates where they bury themselves during droughts.
Taxonomy and Morphology: Fire Eel (Mastacembelus erythrotaenia). Giant Mastacembelid. Thick and muscular, with the classic prominent fleshy rostrum. Can reach 100 cm (39 inches) in length and a build as thick as a man's forearm.
Social Behavior: Despite its mammoth size, it is renowned for unusual intelligence and sociability. After acclimation, it recognizes the owner, lets itself be petted (hand-feeding) and swims like a ribbon in the water.
Coloration and Sexual Dimorphism: Velvety black/anthracite base color. The entire body is longitudinally striated with bright Fire Red/Orange dashes and stripes, while the fins have a bright red margin. The red intensifies in adults.
Care, breeding and tankmates
Aquarium Setup: Final tank no less than 220-250 cm (86-98 inches / min. 1000 Liters / 260 Gallons). Essential very fine sand (not sharp quartz which eviscerates the eel while digging) and gigantic opaque plastic tubes hidden as a permanent den.
Diet and Feeding: Exclusively carnivorous. Adults: whole fish (sardines), shelled prawns, colossal earthworms, mussels and frogs (frozen). Should be fed sparingly (2-3 times a week) as an adult to avoid intestinal blockage or obesity.
Water Quality: Tolerates wide ranges but produces huge waste (Bioload of a freshwater stingray). Over-filtered tanks (Wet-dry or giant Sumps) are a must. Temperature around 26°C (79°F).
Compatibility and Cohabitation: Excellent. Ironically, the "monstrous" Fire Eel is very peaceful. To be kept with Asian Arowanas, Datnioides, and large Barbs (Tinfoil). Will eat any fish that fits in its mouth, but is not quarrelsome or territorial.
Aquarium Breeding: Never documented. Probably linked to migration to monsoon flooded plains, as for other large Asian eels.
Risks and Diseases: Lethal abrasions. The two biggest killers of the Fire Eel in captivity are the use of coarse gravel (which wears down its mucosa to the point of septicemia) and the absence of a weighted lid, leading it to commit suicide on the house floor.
Geographic Origin and Distribution
Southeast Asia (Thailand, Cambodia, Borneo, Sumatra). Large slow or moderate flowing rivers. Clay and muddy substrates where they bury themselves during droughts.
Origin
South and Southeast AsiaEast Asia
Fish profile
- Temperament
- Semi-aggressive
- While highly predatory towards small fish, they are otherwise quite peaceful and shy. They can initially be very reclusive, hiding continuously until they become comfortable in their surroundings. Once acclimated and confident, they can become remarkably tame, often learning to take food directly from their owner's fingers. They possess a surprising amount of personality and intelligence.
- Diet
- Omnivore
- They are strict carnivores that feed primarily on worms, crustaceans, and small fish in the wild. In the aquarium, they relish live or frozen bloodworms, earthworms, blackworms, and ghost shrimp. They can be very picky eaters initially and may require live foods to trigger their feeding response. Over time, some can be trained to accept sinking carnivorous pellets or chunks of seafood.
- Life expectancy
- 10-15 years
- The Fire Eel is a long-lived species that can survive for 10 to 15 years in captivity under proper care. Achieving this lifespan requires a large aquarium with excellent water filtration, as they are sensitive to poor water quality. Providing a soft sandy substrate is crucial, as gravel can damage their skin and lead to fatal infections. A stable diet and avoiding stress from incompatible, aggressive tankmates are also important factors in their longevity.
- Adult size
- 100 cm
- The catalog's scalar value is 100 cm. The FishBase SPECIES table (v25.04 snapshot) source reports a maximum adult measurement of 100 cm for this species, recorded as total length (TL). The taxonomic record consulted is Mastacembelus erythrotaenia (v25.04); male or unsexed record. These figures are not interchangeable: the first is the profile's editorial reference, whereas the second is a published maximum under a specific measurement convention; differences among sources can reflect sex, population, life stage and measuring method.
- Sex ratio
- Solitary
- They are completely solitary by nature and do not require the presence of conspecifics to thrive. Keeping multiple individuals together usually results in severe territorial aggression unless the tank is exceptionally massive. A single individual makes a fantastic and interactive centerpiece for a large custom aquarium. Sexing them visually is impossible for the average aquarist.
- Feeding frequency
- Twice daily
- Adult specimens typically only need to be fed once a day or even every other day. Overfeeding can pollute the water quickly, so only offer what they can consume in a few minutes. Hand-feeding with tongs is a popular and effective method to ensure they receive their share. Juveniles should be fed smaller portions daily to support their rapid growth.
- Bioload
- Extreme
- The Fire Eel produces a heavy bioload, especially as it reaches its massive adult size. High-capacity canister filters or large sumps are strictly required to handle their waste output. Frequent and substantial water changes are absolutely vital to maintain low nitrate levels. Excellent water quality is critical to prevent bacterial infections and skin issues in this scaleless fish.
- Flow
- Stagnant
- They prefer a moderate water flow that ensures good oxygenation without being overwhelmingly turbulent. Good water movement along the bottom of the tank helps sweep away detritus and keeps their environment clean. The flow should not be so strong that it disrupts the sand bed or prevents them from resting comfortably. Providing areas of both higher and lower flow allows them to choose their preferred spot.
- Reproduction
- Oviparous
- Breeding this species in the home aquarium is virtually unheard of due to their size and complex spawning triggers. In the wild, they likely spawn during the rainy season when water levels rise and chemistry changes. The exact details of their reproductive behavior in nature remain somewhat of a mystery. Commercial breeding is rarely successful, meaning most specimens are wild-caught.
- Compatibility & tankmates
- They are generally peaceful towards fish that are too large to be considered prey. Small tank mates like tetras, guppies, and small rasboras will quickly become a midnight snack. Good companions include medium to large robust fish such as gouramis, peaceful cichlids, or large barbs. They generally ignore other bottom-dwelling fish, but ample space is necessary to avoid territorial squabbles.
- Tank level
- Bottom
- They are almost entirely bottom-dwelling fish that spend their time weaving through hardscape and plants. A deep, soft sand substrate is absolutely essential to allow them to bury themselves without scratching their skin. They will often stay completely buried with only their snout protruding, waiting for food. PVC pipes buried under the substrate make excellent permanent hides for them.
Scientific Parameters & Models
Window to the official scientific data of the species
Data synced on: 06/15/2026
- Trophic level
- 2.7 ± 0.27 se
- Resilience
- Low (4.5 - 14 years)
- Phylogenetic uniqueness (PD50)
- 0.5
- Bayesian Length-Weight
- a = 0.00269, b = 2.94
- VulnerabilityHigh vulnerability (60 / 100)
Image gallery
Licensed images linked to the species or, when marked, to the closest representative taxon.
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