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Family: Apteronotidae

Common Name: Black Ghost Knifefish

Origin and Habitat: Widely distributed in the northern half of South America. Found in fast-flowing shallow streams and rivers having a soft substrate, usually sand and leaf litter. During the wet season they move into the flooded forest.

Compatibility/Temperament: A timid fish but predatory, territorial and aggressive within its own species. Should be maintained either as a single specimen or in a group of 6 in a very large tank, never in pairs or smaller groups. It will likely eat small fish, so tankmates should be 6 inches or more. Well suited with angelfish, discus or the medium peaceful South American cichlids such as Geophagus species. Avoid any nippy or aggressive fish. Knifefish produce an electrical field used to hunt prey, and must never be kept with other electric fish.

Black Ghost Knifefish Diet

Naturally a micropredator, eating insect larvae, zooplankton and small fishes. Will sift through the sand substrate when hunting food. In the aquarium, they will appreciate frozen or live bloodworms, small feeder fish, tubifex worms, brine shrimp, ghost shrimp, etc. Can usually be weaned onto prepared foods. Small earthworms are relished and particularly good for getting new fish settled and eating. Nocturnal feeders, they should be fed at night. Once settled, they will often feed during the day, even from the aquarist's hand.


Attains 20 inches, though usually slightly less in the aquarium. Having an inflexible body, it must always have a tank that is wider (front to back) than itself in order to turn.

Minimum Tank Suggestion

6 feet length by 2 feet width; smaller tanks can accomodate the fish as it grows, but the tank should always be no less than triple length and wider than the fish's length.

Water parameters for Black Ghost Knifefish

Soft to medium hard (5-15 dGH), slightly acidic to slightly basic (pH 6 to 8), temperature 23-28C/73-82F, but optimum around 25C/77F.


They have long, laterally compressed bodies with an elongated anal fin that starts at the pectoral fins. The fish's color is jet black with white vertical bands on the tail end. There is also a long white or light yellow stripe going down its back.

This fish is nocturnal; the tank must be dimly-lit, as bright overhead light will keep the fish nervous and stressed. The dim light may make submersed plants difficult to keep, though low light plants such as Anubias and Java Fern may be suitable. Floating plants should always be provided both to shade the light and to maintain more stable water conditions and generate oxygen fro the roots. The aquarium should have a sand substrate and plenty of hiding places in the form of bogwood with crevices and tunnels long enough to accommodate the fish; PVC pipe can also be used to create tunnels. There should be a moderate flow from the filter.

This species is sensitive to any deterioration or fluctuation in water parameters and conditions, and requires a good oxygen level. Should only be introduced to a well-established tank.

Knifefish possess a weakly discharging neurogenic electric organ and ampullary electro receptors that are distributed from head to tail. This is used as a "radar" to detect their surroundings and to locate prey. The body is thus inflexible in order to function as a receptor of electronic signals returning to the fish.

Gender cannot be determined from external features. The species has not been successfully bred in aquaria. There are reports of captive breeding in SE Asia, likely with hormone injection.

There are seven families of knifefishes distributed in South America, Africa and Asia. The five families in South America belong to the order Gymnotiformes; three of these five, namely Apteronotidae, Gymnotidae and Sternopygidae, contain most of the species maintained by aquarists. The subject species is the most widely seen in the hobby of the 22 described species in the genus Apteronotidae. Another smaller species, the brown ghost knifefish, A. leptorhynchus, is sometimes traded. The South American knifefishes are closely related to catfishes, sharing several features including Weberian ossicles, which are small bones that connect the ears to the swim bladder.

Carl Linnaeus, the originator of the system of species classification that developed into the binomial nomenclature system we use today, described this species in his monumental Systema naturae in 1766 and named it Gymnotus albifrons. The species epithet is Latin and refers to the white forehead. Ortega & Vari (1986) moved it into the current genus that was erected by B.G.E. Lacepede in 1800. The genus and family names are from the Greek aptero [= without fins] and noton [= back], referencing the lack of dorsal fins.


Monks, Neale (2009), "Knifefish in the Aquarium," Tropical Fish Hobbyist, Volume LVII, No. 10 (June 2009), pp. 86-90.

Ortega, H. and R.P. Vari (1986), "Annotated checklist of the freshwater fishes of Peru," Smithsonian Contributions to Zoology, No. 437.

Contributing Members

The following members have contributed to this profile: Freddy, Byron


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