Xenomystus nigri
Encyclopedia
Xenomystus nigri, the African Brown Knife Fish or African Knife Fish, is the only species in the genus Xenomystus of the family Notopteridae
. This fish inhabits coastal river basins in Sierra Leone
, Liberia
, Togo
, Benin
and Cameroon
. It also in Chad
, the Nile, the Congo
, and the Niger
basins.
s (12 in
) SL
in length. The body of these fish is unusual, with the body 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, skirtlike 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 knife fish 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 knife fish are extremely small, giving the fish a smooth appearance broken only by its fairly prominent lateral line
. Apart from its eyes, the lateral line is the knife fish's most important sensory apparatus. The African brown knife fish 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 knife fish, when not hiding away, spends much of its time swimming with its head down and the barbels in close proximity with the substrate. Combined with its acute eyes, the barbels aid the fish in locating its food.
of 2 millimetre
s (0.08 in
) in diameter. This species of fish can produce barking sounds. These fish will come to the surface from time to time to swallow air. They feed at dusk and during the night on worm
s, crustacean
s, insect
s and snail
s.
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.
Notopteridae
The family Notopteridae contains eight species of osteoglossiform fishes, commonly known as featherbacks and knifefishes. They are small fishes living in freshwater or brackish environments in Africa and South-east Asia....
. This fish inhabits coastal river basins in Sierra Leone
Sierra Leone
Sierra Leone , officially the Republic of Sierra Leone, is a country in West Africa. It is bordered by Guinea to the north and east, Liberia to the southeast, and the Atlantic Ocean to the west and southwest. Sierra Leone covers a total area of and has an estimated population between 5.4 and 6.4...
, Liberia
Liberia
Liberia , officially the Republic of Liberia, is a country in West Africa. It is bordered by Sierra Leone on the west, Guinea on the north and Côte d'Ivoire on the east. Liberia's coastline is composed of mostly mangrove forests while the more sparsely populated inland consists of forests that open...
, Togo
Togo
Togo, officially the Togolese Republic , is a country in West Africa bordered by Ghana to the west, Benin to the east and Burkina Faso to the north. It extends south to the Gulf of Guinea, on which the capital Lomé is located. Togo covers an area of approximately with a population of approximately...
, Benin
Benin
Benin , officially the Republic of Benin, is a country in West Africa. It borders Togo to the west, Nigeria to the east and Burkina Faso and Niger to the north. Its small southern coastline on the Bight of Benin is where a majority of the population is located...
and Cameroon
Cameroon
Cameroon, officially the Republic of Cameroon , is a country in west Central Africa. It is bordered by Nigeria to the west; Chad to the northeast; the Central African Republic to the east; and Equatorial Guinea, Gabon, and the Republic of the Congo to the south. Cameroon's coastline lies on the...
. It also in Chad
Chad
Chad , officially known as the Republic of Chad, is a landlocked country in Central Africa. It is bordered by Libya to the north, Sudan to the east, the Central African Republic to the south, Cameroon and Nigeria to the southwest, and Niger to the west...
, the Nile, the Congo
Congo River
The Congo River is a river in Africa, and is the deepest river in the world, with measured depths in excess of . It is the second largest river in the world by volume of water discharged, though it has only one-fifth the volume of the world's largest river, the Amazon...
, and the Niger
Niger River
The Niger River is the principal river of western Africa, extending about . Its drainage basin is in area. Its source is in the Guinea Highlands in southeastern Guinea...
basins.
Anatomy and appearance
This fish reaches 30 centimetreCentimetre
A centimetre is a unit of length in the metric system, equal to one hundredth of a metre, which is the SI base unit of length. Centi is the SI prefix for a factor of . Hence a centimetre can be written as or — meaning or respectively...
s (12 in
Inch
An inch is the name of a unit of length in a number of different systems, including Imperial units, and United States customary units. There are 36 inches in a yard and 12 inches in a foot...
) SL
Fish measurement
Fish measurement refers to the measuring of the length of individual fish and of various parts of their anatomy. These data are used in many areas of ichthyology, including taxonomy and fisheries biology.-Overall length:...
in length. The body of these fish is unusual, with the body 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, skirtlike 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
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
is absent. The pectoral fins of the African brown knife fish 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
Scale (zoology)
In most biological nomenclature, a scale is a small rigid plate that grows out of an animal's skin to provide protection. In lepidopteran species, scales are plates on the surface of the insect wing, and provide coloration...
of the knife fish are extremely small, giving the fish a smooth appearance broken only by its fairly prominent lateral line
Lateral line
The lateral line is a sense organ in aquatic organisms , used to detect movement and vibration in the surrounding water. Lateral lines are usually visible as faint lines running lengthwise down each side, from the vicinity of the gill covers to the base of the tail...
. Apart from its eyes, the lateral line is the knife fish's most important sensory apparatus. The African brown knife fish 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 knife fish, when not hiding away, spends much of its time swimming with its head down and the barbels in close proximity with the substrate. Combined with its acute eyes, the barbels aid the fish in locating its food.
Ecology
This fish preferes quiet water with vegetation. Females lay 150–200 eggsEgg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
of 2 millimetre
Millimetre
The millimetre is a unit of length in the metric system, equal to one thousandth of a metre, which is the SI base unit of length....
s (0.08 in
Inch
An inch is the name of a unit of length in a number of different systems, including Imperial units, and United States customary units. There are 36 inches in a yard and 12 inches in a foot...
) in diameter. This species of fish can produce barking sounds. These fish will come to the surface from time to time to swallow air. They feed at dusk and during the night on worm
Worm
The term worm refers to an obsolete taxon used by Carolus Linnaeus and Jean-Baptiste Lamarck for all non-arthropod invertebrate animals, and stems from the Old English word wyrm. Currently it is used to describe many different distantly-related animals that typically have a long cylindrical...
s, crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s, insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s and snail
Snail
Snail is a common name applied to most of the members of the molluscan class Gastropoda that have coiled shells in the adult stage. When the word is used in its most general sense, it includes sea snails, land snails and freshwater snails. The word snail without any qualifier is however more often...
s.
In the aquarium
This species is sometimes available as an aquariumAquarium
An aquarium is a vivarium consisting of at least one transparent side in which water-dwelling plants or animals are kept. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, marine mammals, turtles, and aquatic plants...
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.