The Black Ghost Knife 15/18cm is one of the most unique freshwater fish you can add to a larger aquarium. With its smooth, knife‑shaped body, jet‑black colour and white markings on the tail, the Black Ghost Knife Fish glides through the water using a long undulating fin, giving it a ghost‑like, almost floating appearance.
This species, Apteronotus albifrons, comes from South America where it lives in dimly lit rivers and streams. It’s a nocturnal, electric fish that uses weak electric signals to navigate and find food. Because of its size and sensitivity, the Black Ghost Knife 15/18cm is best kept by intermediate to advanced aquarists who can provide a suitably large, stable aquarium.
Size and Lifespan
- Current size: approximately 15–18cm
- Potential adult size: can grow to around 40–50cm in a suitably large aquarium
- Lifespan: with good care, Black Ghost Knife Fish can live for many years in captivity
When you purchase a Black Ghost Knife 15/18cm, you’re getting a juvenile to sub‑adult fish that will continue to grow. Planning for its adult size and long‑term care is important.
Black Ghost Knife 15/18cm – Tank Requirements
Because of their eventual size and active swimming style, Black Ghost Knife Fish need a spacious aquarium:
- Recommended tank size: a large aquarium (think 4ft+ in length) for a single Black Ghost Knife 15/18cm, with more space as it grows
- Filtration: strong, reliable filtration with good biological capacity
- Décor: plenty of hiding places – caves, pipes, driftwood and plants help the fish feel secure
- Lighting: relatively dim or shaded areas, as Black Ghost Knife Fish are naturally more active at night
Soft sand or smooth gravel is preferred so the fish doesn’t injure its delicate skin when exploring the bottom.
Water Parameters (Guide Only)
The Black Ghost Knife 15/18cm is reasonably flexible if changes are slow and water quality is high:
- Temperature: around 24–27°C
- pH: roughly 6.5–7.5
- Hardness: soft to moderately hard water
- Ammonia & Nitrite: 0 ppm
- Nitrate: kept low with regular water changes
Stable, clean water is more important than chasing exact numbers. Avoid sudden swings in temperature or pH.
Feeding Black Ghost Knife Fish
The Black Ghost Knife 15/18cm is a carnivorous, nocturnal feeder that prefers meaty foods:
- Suitable foods:
- Frozen or live bloodworms
- Brine shrimp
- Blackworms
- Small prawns or shrimp pieces
- Quality sinking carnivore pellets
Feed your Black Ghost Knife Fish in the evening or when lights are dimmed, as they are more confident and active at night. Offer small amounts and remove uneaten food to maintain water quality.
Behaviour and Temperament
Black Ghost Knife Fish are generally peaceful towards other species, but can be territorial with their own kind in smaller tanks:
- Personality: shy to semi‑bold, often hiding during the day and exploring more at night
- Temperament: usually peaceful, but may become stressed or aggressive if crowded or kept with fin‑nippers
- Activity: glides along the bottom and mid‑levels, weaving in and out of décor
Providing enough hides and visual barriers helps your Black Ghost Knife 15/18cm feel secure and show more natural behaviour.
Tank Mates for Black Ghost Knife 15/18cm
Choose tank mates that are:
- Similar size or slightly larger once the Black Ghost Knife Fish is fully grown
- Peaceful to semi‑aggressive, but not fin‑nippers
- Not small enough to be seen as food
Avoid very small fish, aggressive fin‑nippers and other electric knife fish species in the same tank. Always consider the adult size of your Black Ghost Knife 15/18cm when planning long‑term stocking.
Important Notes
- Not recommended for small aquariums – plan for the adult size of the Black Ghost Knife Fish.
- Sensitive to poor water quality – regular maintenance and good filtration are essential.
- Provide plenty of hiding spots so your Black Ghost Knife 15/18cm feels secure and settles in well.
