Fire Eel

About

The fire eel is the largest spiny eel in the aquarium trade and the one most often bought on impulse at 15 cm, with no plan for the metre of fish it becomes. FishBase, Seriously Fish, Maidenhead Aquatics and AquaInfo all give the adult as 100 cm; Practical Fishkeeping is the dissenting voice, putting the verified maximum at 80 cm and calling reports of a metre or more unconfirmed. Either figure outgrows every aquarium a shop sells. It is not an aggressive animal - Seriously Fish calls it a generally peaceful community fish - but it is a nocturnal predator, and Maidenhead's line is blunt: adults will take small fish overnight. The rest of the difficulty is mechanical rather than behavioural. It burrows, so the substrate has to be soft sand, and every rock and root must stand on the tank base with the sand poured in around it, because a large specimen undermines a decor pile and ends up crushed beneath it. And it escapes: Seriously Fish writes that the eel 'can find its way through the smallest of gaps', Maidenhead calls them great escape artists, and an escaped spiny eel is a dead spiny eel. Sources disagree about plants, which is worth knowing before you buy: Practical Fishkeeping advises keeping rooted plants to a minimum or dispensing with them altogether because of the burrowing, while Seriously Fish asks for a well-planted tank and AquaInfo for dense plant cover. Expect to lose the odd stem, not the planting.

Care

Sand, never gravel, with the hardscape standing on the glass before the substrate goes in. AquaInfo asks for a tank from 200 cm long, about 500 litres; Seriously Fish and Practical Fishkeeping quote 120 x 60 x 60 cm, and for a fish this length the larger figure is the honest one. 24-28 °C, pH 6.2-7.2 (tolerated 6.0-8.0), dim light, gentle flow, and abundant cover in caves, pipes, bogwood and plant thickets, because the eel stays buried through the day. Every gap in the lid has to be blocked rather than merely covered, including where equipment feeds through. Keep one unless the tank is exceptional: peaceful towards fish too large to swallow, territorial towards its own kind, and groups of five or more only where there is room for every fish to hold its own burrow. Any tankmate must be too big to fit in that mouth.

Diet

Omnivorous in the wild, carnivorous in practice. Frozen bloodworm, white mosquito larvae and brineshrimp for juveniles; prawn, krill, mussel, lancefish and earthworm for adults. Dried foods are rarely accepted, and small frozen foods alone will not carry an adult.

Telling males from females

There is no reliable way to sex this species by eye. That is the honest answer, not a gap in our data.

Also in these lists

Similar species

Same category and the closest water parameters — if this species isn't quite it, start here.

Sold in Lithuania

These Lithuanian shops listed this species in their public catalogue (checked August 8, 2026). Stock moves — ask before you travel.

These links are unpaid: we get nothing for them and ask for nothing.

Frequently asked questions

What tank size does a Fire Eel need?

A Fire Eel needs an aquarium of at least 500 litres (132.1 US gallons) with a footprint at least 200 cm (78.7 in) long — for this species, swimming length matters as much as raw volume.

What water parameters does a Fire Eel need?

Fire Eel does best at 24–28 °C (75.2–82.4 °F), pH 6–8 and a general hardness of 5–19 °dGH.

Is the Fire Eel suitable for beginners?

Fire Eel is a demanding species best attempted with some experience — it needs stable, closely watched conditions to thrive.

Sources

• FishBase — Mastacembelus erythrotaenia (Fire eel)
• Seriously Fish — Mastacembelus erythrotaenia (Fire Eel)
• Maidenhead Aquatics (Fishkeeper) — Fire Eel, Mastacembelus erythrotaenia
• Practical Fishkeeping — How do I keep a Fire eel in the aquarium? (Dr Heok Hee Ng)
• AquaInfo — Mastacembelus erythrotaenia (Fire Eel)