African Knifefish Xenomystus Nigri
African Knifefish Xenomystus Nigri
© Andy Lewis

African Knifefish

Xenomystus nigri
SynonymsNotopterus nigri, N. nili
DistributionAngola, Benin, Cameroon, Chad, Congo, Democratic Republic of the Congo, Egypt, Gabon, Liberia, Nigeria, Sierra Leone, Sudan, and Togo.
Sexual DimorphismDifficult to sex. Mature females in breeding condition may appear fuller bodied.
Maximum Size30cm (11.8")
Temperature22-28 deg C (72-82 deg F)
Water ParametersWill acclimatise to a wide range of conditions. pH: 6.0-8.0, dH: up to 20 degrees.
CompatibilityCommunity of medium-sized fish.


The African Knifefish has a wide area of distribution throughout tropical Africa, including the Chad, Congo, Niger, Nile, and Ogowe basins. Although it is found in a variety of different water parameters, it prefers quieter areas with an abundance of aquatic vegetation. This nocturnal predator tends to seek refuge in dimly lit, sheltered nooks and crannies during the day, emerging at night to feed on crustaceans, insects, snails, and worms. The African Knifefish is reasonably easy to keep, provided that some key requirements are met. Firstly, this fish grows fairly large and cannot really bend, so a spacious aquarium (at least 4ft long and a minimum 18" wide) is a must. Secondly, the knifefish must be provided with a choice of shady hiding spots e.g. wide PVC tubes, flowerpots on their sides, rocky caves/overhangs (do ensure such structures are stable), and large tangles of driftwood. The lighting should not be too bright as these nocturnal fish are sensitive to intense illumination; if the tank must be brightly lit in some areas, provide plenty of broad leaved aquatic plants and floating species to help diffuse the light. Nonetheless, there absolutely must be areas of darkness within the tank that the fish can retreat to during the day as necessary. The substrate should consist of soft sand in order that the fish may grub about safely when searching for food, and so that the delicate anal fin does not become torn in any sharp gravel. Decent filtration, and moderate levels of flow and oxygenation are required, along with a consistent maintenance regime encompassing regular partial water changes, as these fish are sensitive to elevated nitrate and sudden changes in water chemistry. African Knifefish are generally peaceful with other fish (which are large enough not to be eaten overnight), but they are territorial with their own kind and other knifefish, so should be kept one to a tank and not with any other knifefish species. Tankmates should be of similar temperament and large enough not to be considered a snack; good companions could include angelfish, eartheaters (Geophagus spp.), medium-sized gouramis, medium-sized characins, large rainbowfish, African Butterfly Fish, Synodontis catfish etc. Avoid housing with any aggressive or boisterous species, and do not attempt to keep alongside snails or shrimps as these would be predated upon. When first introduced to the aquarium, the African Knifefish is often very shy, but over time, it will gain confidence - indeed, some specimens may become so tame that they may take food from the hand of the aquarist, or even sit in the hand itself whilst feeding. Blue moon lighting, timed to come on just before the main lights switch off in the evening, is useful in observing your knifefish for a few hours under its preferred subdued lighting. Due to a specially adapted swim bladder which acts as an accessory breathing organ, African Knifefish need to take in warm air from above the water’s surface periodically, so a small gap must be left between the surface of the water and the cover slides in order for the fish to accomplish this. The knifefish may emit an audible bell-like sound as it takes in air. Hopefully, if the tank is maintained appropriately and new fish are quarantined carefully before adding the main aquarium, the need for medications should not arise. However, if treatment is required, take much care as these fish are classed as 'scaleless' and are particularly sensitive to medications (always check with the manufacturer before using - some treatments are not safe, and others may need half dosing). Many aquarists also find that running a UV steriliser on the tank helps to eliminate pathogens and safeguards against the need for putting treatment in the water.


African Knifefish are micro-predators and should be offered a variety of small, meaty foods. Frozen fare could include bloodworm, white/black mosquito larvae, vitamin-enriched brineshrimp, Mysis shrimp etc, along with some dried foods such as slow sinking granules/pellets for carnivores. At least one feed per day should be after lights out (or under blue moon lighting).


This species has been bred in the home aquarium, but few details are available. It is not a common occurrence because most aquarists can only house one per tank due to their territorial nature. During courtship, the pair are said to produce audible 'barking' sounds. 150-200 eggs are reportedly deposited/fertilised in a suitable crevice during the night, which the male then guards. The eggs should hatch within 6-9 days (temperature dependent) and can be offered baby brineshrimp (Artemia nauplii). The adults will predate on the young, so it may be best to transfer them to another aquarium once the eggs begin to hatch.

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