Rope fish

Water parameters

Tolerated range for this species. Aim for the middle of each band rather than the extremes.

Tank and habitat

Substrate: sand.

Behavior

Plant interaction: plant safe.

Typically wild-caught; acclimate slowly.

Feeding

Carnivore that prefers live and frozen meaty food. Frozen bloodworm, frozen prawns, frozen mysis, live earthworms, live blackworms, and live feeder shrimp are the core diet. They hunt by smell rather than sight, weaving their body across the substrate to locate food. Pellets are reluctantly accepted by some individuals but many refuse dry food entirely. Feed after lights-out when the rope fish is active. In community tanks, ensure food reaches the bottom before other fish intercept it. Feed every other day for adults; daily for juveniles. They eat slowly and may take 10-15 minutes to finish a meal.

Nocturnal feeder; drop food after lights out.

Compatibility

• Peaceful despite looking predatory. Rope fish ignore tankmates that are too large to swallow, which in practice means anything over 5–6 cm. Small fish (neons, guppies, small rasboras) and shrimp are eaten.
• Best with medium to large peaceful community fish: larger barbs, rainbowfish, medium cichlids, larger tetras, and catfish. Avoid housing with aggressive species that would harass the slow-moving rope fish.
• Nocturnal. They hide during the day and become active at dusk. Expect to rarely see them during daylight hours unless the tank is dimly lit with plenty of hiding spots.
• Escape artists of the highest order. Rope fish squeeze through any opening in the lid, climb filter tubing, and exit through gaps around equipment. Sealing the tank completely is mandatory. They can survive out of water for extended periods by breathing air through a primitive lung, so rescue fish from the floor promptly.

Origin and habitat

Native to West and Central Africa. The confirmed range is that of a coastal species inhabiting river estuaries from the Ouémé River in Benin to the Sanaga River in Cameroon; a record from the Chiloango River (Congo) exists but needs confirmation. Also reported from the Ogun River in Nigeria to the Chiloango. The only member of its genus (Erpetoichthys); belongs to the family Polypteridae alongside bichirs. The genus name comes from Greek erpeton ("creeping thing") + ichthys ("fish"). Listed as IUCN Near Threatened. Found in slow-moving or standing fresh and brackish water, apparently restricted to reedy habitats. Elongated, eel-like body with a series of well-separated dorsal finlets and no pelvic (ventral) fins, distinguishing it from all Polypterus species. Greenish-black dorsal surface with a yellow ventral surface. Grows to a maximum of about 37 cm standard length; around 30 cm is typical. Possesses a primitive lung in addition to gills, accounting for roughly 40% of its oxygen uptake; the remainder splits between gills and skin. Can survive up to eight hours out of water if its skin stays moist. Nocturnal; feeds on worms, crustaceans, and insects at night. Breeding has rarely if ever been documented in home aquariums; most or all trade specimens are wild-caught. Larvae have external gills resembling salamander larvae.

Breeding

Not bred in home aquariums. The reproductive biology in the wild is poorly documented. Males reportedly have a thicker, wider anal fin that functions as an intromittent organ for internal fertilization, which is unusual for fish. Spawning in the wild likely occurs during the rainy season in flooded vegetation. Eggs are reportedly deposited among aquatic plants. No reliable captive breeding has been achieved in the hobby despite decades of keeping the species. Sexing is difficult; the anal fin difference between males and females is subtle and requires comparison of multiple specimens. Every rope fish in the trade is wild-caught.

Common problems

Escaping is the number one problem. A rope fish in a tank with any unsecured opening will find it. They're thin enough to squeeze through gaps that seem impossibly small. Cover every opening: filter intake slots, cable entry points, overflow holes, and the gap between the lid and the back of the tank where equipment enters. Refusal to eat dry food is common; many individuals need live or frozen food exclusively, which increases the keeper's workload. Starvation in community tanks happens when all the food is eaten by faster tankmates before the nocturnal rope fish emerges. After-hours feeding solves this. Skin infections and fungal issues appear when water quality degrades; the scaleless body is vulnerable. Avoid salt treatments. Provide dim lighting and plenty of hiding spots (PVC pipes, driftwood tangles, dense plants) to reduce daytime stress.

Bioload

Further reading

• How to cycle a fish tank
• Stocking ideas by tank size