Rope fish

Quick facts

Adult size

35 cm

Lifespan

can live up to 20 years

Tank zone

bottom

Temperament

peaceful

Difficulty

intermediate

Typically wild-caught

yes - acclimate slowly

Water parameters

Temperature

24–28°C

pH

6.0 to 8.0

Hardness

5 to 20 dGH

Tank requirements

Minimum volume

250 L

Minimum length

120 cm

Flow

low

Lighting

dim preferred

Substrate

sand

Driftwood

preferred

Hiding spots

needed

Lid

required - jumper

Feeding

Diet: carnivore, feeds primarily at the bottom.

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 so it can eat without competition.

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.

Habitat

Native to slow-moving rivers, swamps, and floodplain waterways in West and Central Africa, from Nigeria through Cameroon to the Congo basin. Found in heavily vegetated, warm, low-oxygen water. The species (Erpetoichthys calabaricus) is the only member of its genus and belongs to the family Polypteridae, making it a relative of bichirs. The body is elongated and snake-like, up to 37 cm (though 25–30 cm is more typical in captivity), with a row of small dorsal finlets running along the back. No pelvic fins. The body color is uniform olive-green to brown with a pale underside. The species has a functional swim bladder modified as a primitive lung, allowing it to breathe atmospheric air. In the wild, this allows survival in oxygen-depleted swamp water. In the tank, you'll see them rise to the surface periodically to gulp air, which is normal behavior. The species has been in the hobby since at least the 1960s. All specimens are wild-caught from African river systems; captive breeding is essentially non-existent in the hobby.

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

Bioload coefficient: 5.0 (long-bodied; moderate waste output relative to length).

Bioload coefficients are calibrated against the neon tetra as the anchor (1.0). See the methodology page for the formula and how each value was derived.

Further reading

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