From Boulenger (1909, pp. 147-148)
Depth of body 4 1/3 to 5 times in total length, length of head 6 to 7 1/3 times. Snout very short, shorter than eye, the diameter of which is 3 to 3 1/2 times in length of head and equals or nearly equals interocular width; mouth extending to below anterior third or centre of eye; nasal tentacle long and attenuate, 3/5 to 2/3 diameter of eye; preorbital, suborbitals, preoperculum, and mandible with the edge strongly serrated; preoperculum with a serrated ridge, parallel with the lower border. Gill-membranes extending without a notch across the isthmus. Gill-rakers very short, tubercular, 9 to 11 on lower part of anterior arch. Anal 108-130 (including caudal). Pectoral as long as head or a little shorter. Ventral serrature formed of 26-30 pairs of spines. Pelvic fins greatly reduced. Lateral line 120-142.
Central Africa: Xenomystus nigrii is known from Pool Malebo (Stanley Pool) and from the Lower and Central Congo River basin. It has also been recorded from just upstream Kisangani. It is known from the Lower Guinea region where it occurs in the Wouri River, Cameroon and in the Ogowe River and coastal drainages in Gabon.
Northeast Africa: It is present in the Bahr el Jebel system, Sudan.
Western Africa:Within Western Africa, Xenomystus nigri has been reported from Sierra Leone (Lake Kwarko Krim and River Gbap), Liberia (Farmington Lake), Togo (Togble-Kope River, Kelegougan flood plain), and from Benin to Nigeria and the Chad basin.
- Roberts, T.R. 1992 Systematic revision of the old world freshwater fish family Notopteridae. Ichthyol. Explor. Freshwat. 2(4):361-383. (Ref. 7431)
Widespread in Congo Basin. In Lower Guinea, occurs in the Wouri River, Cameroon and in the Ogowe River and coastal drainages in Gabon. Elsewhere, it is found in the Nile, Chad, Niger River basins, and coastal drainages from Sierra Leone, Liberia, Togo, and Benin. It is apparently absent from the Volta, and from Ivory Coast.
- Olaosebikan, B.D. and A. Raji 1998 Field guide to Nigerian freshwater fishes. Federal College of Freshwater Fisheries Technology, New Bussa, Nigeria. 106 p. (Ref. 31256)
to 200 mm SL
Distinguished from other notopterids by the absence of a dorsal fin, only 3 branchiostegal rays, and rudimentary gill rakers. Lacking the distinctive spotted color markings typical of Papyrocranus afer, it may be easily distinguished from this species in areas where they co-occur.
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Barcode data: Xenomystus nigri
Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.
See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
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Statistics of barcoding coverage: Xenomystus nigri
Public Records: 13
Specimens with Barcodes: 15
Species With Barcodes: 1
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African brown knifefish
The African brown knifefish or African knifefish, Xenomystus nigri, is the only species in the genus Xenomystus of the family Notopteridae. This fish is found in the Chad, Nile, Congo, Ogowe and Niger basins, as well as coastal river basins in Sierra Leone, Liberia, Togo, Benin and Cameroon.
Anatomy and appearance
This fish reaches 30 cm (12 in) in length. The body of these fish is unusual; it is ventrolaterally flattened and elongated, giving the appearance of a knife blade. The caudal and anal fins are fused and run from beneath the gill opening to the pointed end of the body, creating a uniform, skirt-like fin. This appendage gives the animal superior control in the water, as it is able to propel itself forward and backward with a minimum of wasted energy. The pelvic fins are extremely reduced and are not used in locomotion. The dorsal fin is absent. The pectoral fins of the African brown knifefish are lengthy and designed to give the animal precise control as it swims. They are often employed in a windmilling motion, in conjunction with the caudal/anal fin, as the fish retreats into its lair.
The scales of the knifefish are extremely small, giving it a smooth appearance broken only by its fairly prominent lateral line. Apart from its eyes, the lateral line is the knifefish's most important sensory apparatus. The African brown knifefish is nocturnal and uses the nerve-filled pits running down its body to navigate lightless waters. In addition, the eyes of this fish are large in relation to its body size. They provide the animal with excellent night vision.
The mouth is large, and the fish also possesses a pair of short barbels used in hunting. The knifefish, when not hiding away, spends much of its time swimming with its head down and the barbels in close proximity to the substrate. Combined with its acute eyes, the barbels aid the fish in locating its food.
This fish inhabits quiet water with vegetation. Females lay 150–200 eggs of 2 mm (0.08 in) in diameter. This species can produce barking sounds. They come to the surface from time to time to swallow air. They feed at on worms, crustaceans, insects, and snails.
In the aquarium
This species is sometimes available as an aquarium fish, and has been popular in the hobby for a long time. Because this fish is primarily nocturnal, it will retreat from brightness in the aquarium. When larger, these fish may prey upon smaller tankmates  as these fish have relatively large mouths for their size. This fish does well when kept in small groups when young, although as it ages, it becomes somewhat aggressive towards those of its own kind.
- Froese, Rainer and Pauly, Daniel, eds. (2007). "Xenomystus nigri" in FishBase. Apr 2007 version.
- Axelrod, Herbert, R. (1996). Exotic Tropical Fishes. T.F.H. Publications. ISBN 0-87666-543-1.
- Innes, Dr William T. Exotic Aquarium Fishes, 19th edition, Innes Publishing Co. Philadelphia, 1956.