Sternopygus macrurusLongtail knifefish

Geographic Range

Sternopygus macrurus occurs in many freshwater bodies in South America. It is known to inhabit the area from the Magdalena River to the Sao Francisco River and western Ecuador. It is also found in the Catatumbo River and the Amazon in Peru. (Ortega and Vari 1986)


Sternopygus macrurus is most common in benthopelagic and freshwater bodies such as swamps, creeks, and rivers with lentic waters. The pH range for S. macrurus is 6.0 to 6.5 and the dH range is 4.0 to 15.0. (Ortega and Vari 1986)

  • Aquatic Biomes
  • benthic
  • rivers and streams

Physical Description

Sternopygus macrurus is a knife-shaped fish. It has a slender body with a tapering tail. The maximum length of the Longtail Knifefish is 100.0 cm in total length. S. macrurus is an electric fish. From the larval stage on, an electric organ and electroreceptors are present. (Kirschbaum 1995)


The male Sternopygus macrurus defends a territory. Just before or during the rainy season, the male will attract a female passing though his territory as a spawning partner. He attracts a female using electric signals from his electric organ. A single mating results in over 6000 eggs. (Hopkins 1972; Provenzano 1984; Kirschbaum 1995)


After four days, the Sternopygus macrurus embryos hatch from the eggs. Seven days later, the larvae make their first feeding. The fish reaches sexual maturity at the age of one year. Mature males are territorial. The species is considered harmless to humans. (Kirschbaum 1995; Moller 1995)

Communication and Perception

Food Habits

Sternopygus macrurus is a predator of small invertebrates. Its diet is mainly composed of aquatic insect larvae. (Planquette, Keith, and LeBail 1996)

Economic Importance for Humans: Positive

Sternopygus macrurus is commercially important in fisheries and aquariums. (Ortega and Vari 1986)

Economic Importance for Humans: Negative


Conservation Status


William Fink (editor), University of Michigan-Ann Arbor.

Niki Piotrowski (author), University of Michigan-Ann Arbor.



living in the southern part of the New World. In other words, Central and South America.

World Map


Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


uses smells or other chemicals to communicate


having the capacity to move from one place to another.


specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.


uses touch to communicate


Hopkins, C. 1972. Sex differences in electric signalling in electric fish. Science, 176: 1035-1037.

Kirschbaum, F. 1995. Reproduction and development in mormyform and gymnotiform fishes. Pp. 267-301 in P Moller, ed. Electric fishes:history and behavior. London: Chapman & Hall.

Moller, P. 1995. Electric Fishes: History and Behavior. London: Chapman & Hall.

Ortega, H., R. Vari. 1986. Annotated checklist of the freshwater fishes of Peru. Smith. Contrib. Zool., 437: 1-25.