A velvety-black, knife-shaped weakly electric fish from South America that glides forward and backward with a single undulating anal fin. Nocturnal, intelligent and personable, it navigates and hunts via a self-generated electric field, but it grows large and needs a big, mature tank.
ℹ️
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Up to 45-50 cm (18-20 in); typically 30-40 cm in aquaria
Lifespan
10–15 years
Social needs
solo
Native region
Amazon and Paraná river basins, South America
Origin
New World
Climate
🌴 Tropical
Water type
💧 Freshwater
Family
Apteronotidae
Genus
Apteronotus
Part of the Freshwater oddballs
Unusual, conversation-piece freshwater fish — knifefish, elephantnoses, bichirs, butterflyfish and other novelties prized for strange shapes, behaviors or electric senses rather than schooling color.
From the minimum an animal needs to be kept humanely, up to the ideal setup. Bigger is almost always better — minimums are floors, not targets.
Photo coming soon
Minimum
Sub-adult species tank
75 gal / 284 L long tank
Apteronotus albifrons grows to 18–20 in. A 75-gallon long is barely adequate for a juvenile — adults need more. Soft slightly acidic water, dim lighting, sand substrate, and a tube or driftwood hide for the nocturnal fish to rest in.
Photo coming soon
Recommended
Adult planted tank
125 gal / 473 L long, dim
125-gallon long with multiple long PVC tubes or driftwood hollows, sand bed, dim or red lighting, and gentle flow. They use electrolocation — keep electrical interference low. Peaceful but eat anything bite-sized.
Photo coming soon
Ideal
Amazon biotope display
180 gal+ / 681 L+ Amazon biotope
Six-foot+ Amazon biotope with blackwater, leaf litter, multiple cave/tube hides, sand, and gentle current. Allows adult swim behaviour and natural nocturnal hunting.
Life & growth stages
How this animal changes through its life — each stage often has its own care, diet and space needs.
Photo coming soon
Egg
Fish eggs are small, translucent spheres, often laid in clutches on plants, substrate, or in a nest — or carried/brooded by a parent in livebearing and mouth-brooding species. A dark eye spot and the curled embryo become visible inside as development progresses.
Photo coming soon
Fry
Newly hatched fry are tiny and semi-transparent, frequently still carrying a yolk sac that fuels them before they feed freely. They lack full fin structure and adult coloration, staying near cover until they can swim and forage on their own.
Photo coming soon
Juvenile
Juveniles look like miniature adults but with developing fins and muted or different markings; many species shift pattern and color as they mature. Growth is rapid at this stage given clean water and steady feeding.
Adult
Adults show the species' full size, finnage, and mature coloration, and are sexually mature. Many fish develop sex-specific differences in size, color, or fin shape, which can intensify during breeding.
Habitat & enclosure
Provide a minimum of 380 L (100 gal) for a single adult; juveniles can start smaller but grow fast. Soft to moderately hard water, pH 6.0-7.5, temperature 23-28 C (73-82 F), and gentle to moderate flow suit it best.
Low, subdued lighting and plentiful shaded cover are essential — this is a nocturnal, light-shy species. Floating plants and dim lights coax it out during the day.
Substrate
Use soft sand or smooth fine gravel to protect the scaleless body. Build caves, driftwood tangles, PVC tubes, or rock overhangs so it has a dark daytime retreat.
Equipment & setup
Run robust biological filtration with gentle-to-moderate outflow and a heater rated for the large volume. Subdued LED lighting (or a moonlight setting) and a tight-fitting lid are important, as these fish can jump and dislike bright light.
Diet
Carnivore. Offer frozen and live bloodworms, blackworms, brine shrimp, chopped earthworms, and sinking carnivore pellets. Feed in the evening when active; it readily learns to take food from the keeper's hand.
Behavior & temperament
Generally peaceful but predatory — it will eat any fish small enough to swallow, so keep only with medium, calm tankmates (larger tetras, rainbowfish, geophagus-type cichlids, bristlenose plecos). Adults can be territorial toward other knifefish and electric species due to overlapping electric fields; one ghost knife per tank is safest unless the system is very large.
Health
Scaleless and sensitive to ich, velvet, and poor water quality; dose medications at half strength and avoid copper. Highly intolerant of ammonia, nitrite, and dissolved metals — only add to a fully cycled, stable tank. Susceptible to skin infections and bullying-related stress.
Tips, DIY & hacks
Drip-acclimate slowly and quarantine before introducing, as scaleless fish stress easily. A length of dark PVC pipe makes a perfect, inexpensive cave that the fish will adopt as a home and even feed from. Never use copper-based or full-dose scaleless-sensitive medications.
