African Knife Fish
Xenomystus nigri
A nocturnal, air-breathing brown knifefish that glides on a long fin.
| Difficulty | Intermediate |
| Min. Tank Size | 200 L |
| Temperature | 23.0–28.0 °C |
| pH Range | 6.0–7.5 |
| Max Size | 20.0 cm |
| Lifespan | 8-10 years |
| Diet | Carnivore |
| Temperament | Peaceful |
Overview
The African Knife Fish (Xenomystus nigri) is a nocturnal, air-breathing brown knifefish that glides on a long fin. It is a popular choice among Australian aquarists, reaching around 20 cm and living roughly 8-10 years when properly cared for.
This complete guide covers how to keep the African Knife Fish successfully - tank size and setup, water parameters, the best foods (including recommended brands), suitable tank mates, breeding, sexing and the health issues to watch for. It is rated Intermediate to care for.
Natural Habitat & Origin
This species is an 'oddball' - an unusual, often ancient or predatory fish from tropical rivers. It needs a large tank, a very secure lid, plenty of cover, and pristine, well-oxygenated water.
Matching the temperature, water chemistry and cover a species evolved with is the simplest route to keeping it healthy and seeing its natural behaviour and colour.
Tank Size & Aquarium Setup
Provide a minimum of 200 litres for the African Knife Fish. Give it a large footprint with sight-breaks and cover to reduce territorial aggression.
A tight-fitting lid is essential - this species is a capable jumper.
Live plants, driftwood and shaded retreats give security and show off the fish's colours against a natural backdrop.
Always add fish only to a fully cycled, mature tank with stable biological filtration. Provide strong, well-oxygenated flow for this active, oxygen-hungry species.
Water Parameters
Keep the African Knife Fish in stable water at 23-28 °C with a pH of 6.0-7.5. It adapts to a moderate range, so stability matters more than an exact figure.
Test regularly: ammonia and nitrite must read zero, and nitrate should be kept low with routine partial water changes. Always dechlorinate and temperature-match new water, because sudden swings cause far more illness than water that is stable but slightly imperfect.
Diet & Feeding
The African Knife Fish is a carnivore and needs a protein-rich, meaty diet.
In Australia, good options include Hikari Carnivore/Massivore pellets, API Carnivore food and Dymax frozen bloodworm, brine shrimp, krill and mussel. Feed small amounts once or twice a day (only what is cleared in a minute or two), vary the diet for the best colour and health, and avoid overfeeding, which is the leading cause of poor water quality.
Temperament & Tank Mates
The African Knife Fish is peaceful and community-friendly. It mixes well with other calm species that share its temperature (23-28 °C) and pH (6.0-7.5) needs, are too large to be eaten and not large enough to eat it.
Breeding
The African Knife Fish is rarely or not bred in the home aquarium; most stock is commercially farmed or wild-collected, and home breeding is considered very difficult.
Even if you are not planning to breed it, recognising this behaviour helps you understand what you are seeing and respond well - for example by adding cover for fry or giving a guarding pair extra space.
How to Tell Males from Females
These species are usually very difficult to sex visually, with no reliable external differences outside breeding condition.
Common Health Problems
Like most aquarium species it can suffer from white spot (ich), fin rot and fungal or bacterial infections, almost always triggered by stress or poor water quality. Quarantine new arrivals for 2-4 weeks and watch daily for early signs such as loss of appetite, unusual hiding, clamped fins or laboured breathing - caught early, most issues are very treatable.
Prevention beats cure: keep water pristine, avoid overstocking and overfeeding, quarantine new arrivals, and act at the first sign of trouble.
Is the African Knife Fish Right for You?
The African Knife Fish suits keepers with some experience and a stable, mature, appropriately sized tank, as long as you can provide at least 200 litres, water at 23-28 °C and pH 6.0-7.5, the right diet and suitable tank mates.
Meet those needs and the African Knife Fish will reward you for around 8-10 years. Use our free aquarium calculators to plan your setup, and explore our other fish, plant and disease guides to build a thriving aquarium.
