Indonesian Spiny Eel

Mastacembelus unicolor is a large and robustly built spiny eel distributed across the blackwater and clearwater rivers of Borneo and Sumatra. As its species name suggests, it has a relatively uniform body colouration of mid-brown to grey-brown without the bold patterning of fire or tire track eels, though this subtlety can be appreciated in the right lighting.

Despite its understated appearance, this is an impressive fish: large, powerful, and long-lived. It requires a very large aquarium with deep fine sand, excellent filtration, and a fully sealed lid. The naturally acidic, soft blackwater conditions of Borneo should be replicated with appropriate substrate and peat or leaf litter.

Earthworms, prawns, mussel, and frozen fish flesh are all accepted. It is peaceful toward tankmates too large to be consumed and can coexist with large robust species typical of Borneo blackwater: giant gourami, arowana, large barbs, and predatory catfish. Its size and bioload demand a serious commitment from the keeper.

Water: Soft and acidic, pH 6.0–7.0, temperature 24–28°C, GH 1–8, KH 0–3. Tank: Minimum 280 L, deep fine sand, blackwater conditions, very strong filtration, sealed lid. Feeding: Carnivore; earthworms, prawns, mussel, frozen fish, and sinking pellets. Breeding: Not documented in captivity. Compatibility: Large robust Bornean community fish; avoid small species.