The African knife (Xenomystus nigri) is a medium sized fish native to parts of Nigeria, Cameroon, the Democratic Republic of Congo, Egypt, Chad, Liberia, Gabon, Togo, Sudan, Benin, Sierra Leone and Angola. It has been recorded from numerous major rivers including the Nile, Congo and Niger systems. This fish grows to an adult size of 8 to 12 inches long. Females knives are more plump than males when full of eggs. There are no other distinguishing features between the sexes.
The African knife has a swim bladder that is specially adapted to act as an accessory breathing organ in a similar fashion to Polypteriids. It must rise to the surface to take a gulp of air periodically, often emitting a bell like sound when it does so.
The African knife should be maintained in an aquarium of 50 gallons or larger. Smooth rocks, driftwood (ZM2000) and live or artificial plants may be used, as well as a sand substrate (CS7538). These fish can look great in a heavily planted tank with a dark substrate and floating plants to diffuse some of the light.
The African knife prefers a temperature of 73°F to 82°F, a pH of 5.8 to 7.5, and a hardness of 1 to 20°H. Be sure water is clean and well oxygenated.
The African knife is not suitable for a community aquarium. It is a predatory fish that will eat any fish small enough to swallow. Good tank mates include larger characins, medium sized peaceful cichlids, butterfly fish and catfish such as Synodontis, Brochis and Loricariids. It can be kept in a group when young, but as it matures it becomes increasingly territorial, particularly towards conspecifics and a relatively large tank is required to maintain a group of adult knife fish.
The African knife will readily adapt to being fed in the aquarium and will accept most meaty live and frozen foods. Some specimens may also learn to take dried foods. Feed a varied diet including blood worms (SF4792), krill (SF7136), chopped mussel, earthworms, and carnivore pellets (HIK6796). For maximum color, growth, and health these fish will look their best when given probiotics (AL169) in addition to a balanced diet.