knifefish

Knifefish is a common name for several groups of freshwater fishes characterized by slender, knife-like bodies. The term encompasses two major lineages: the Old World knifefishes of the family Notopteridae (found in Africa and parts of Asia) and the New World knifefishes in the order Gymnotiformes (native to tropical regions of the Americas). Members of both groups have elongated, laterally compressed bodies and a long anal or dorsal fin running most or all of the length of the body, which they use to swim with a smooth, undulating propulsion. They typically lack a true caudal fin.

New World knifefishes (Gymnotiformes) are known for their electric organs; many species produce weak electrical fields used for navigation and communication, and a few relatives can generate stronger shocks. Old World knifefishes (Notopteridae) are not electric and are often more robust, with long dorsal fins and forked tails; they are popular in riverine habitats and as ornamental aquarium subjects.

Habitat and behavior: Knifefishes inhabit freshwater environments such as rivers, swamps, and floodplains with vegetated bottoms and slow to moderate currents. They are generally nocturnal and hide among vegetation or substrates during the day. Diet typically consists of invertebrates, crustaceans, insect larvae, and small fish; some species are omnivorous.

In aquaria and conservation: Several knifefish are kept in home aquariums, requiring spacious, well-filtered tanks and secure lids. Some species grow large and may be aggressive toward smaller fish. Habitat loss, pollution, and overfishing threaten several species, while others persist as common, adaptable aquarium inhabitants.