English: Neotropical knifefish; South American knifefish.
Temporal range: Late Jurassic–Recent.
Genera: 34; 250 species; 5 families.
Region: humid Neotropics, southern Mexico to northern Argentina.
Habitat: freshwater, occasionally brackish water; rivers, streams; in small nonfloodplain streams, rivers, floodplain floating meadows, aquatic macrophytes; large rivers.
Use: aquarium trade.
ZoologyFish; nocturnal; capable of producing electric fields for navigation, communication, in the case of the electric eel (
Electrophorus electricus), attack and defense.
Form: long, slender, narrow bodies; tapering tails.
Behavior: swim using undulations of their elongated anal fin, moving backwards as easily as they move forward; fin rays during locomotion, into the direction of motion; the wave motion resembles traveling sinusoidal waves, producing a system of linked vortex tubes along the bottom edge of the fin; the speed is directly related to the frequency of the waves generated; the body is kept relatively rigid.
Fins: no pelvic fins nor dorsal fins; greatly elongated anal fins, stretching along almost the entire underside of their bodies; 150 fin rays along its ribbon-fin, able to curve nearly twice the maximum recorded curvature for ray-finned fish; caudal fin is absent, or greatly reduced.
Gill: gill opening is restricted; anal opening is under the head or the pectoral fins.
Electricity: the electric organs are derived from muscle cells, in adult apteronotids from nerve cells; the electric discharge may be continuous or pulsed, if continuous, it is generated day and night throughout the entire life of the individual; aspects of the electric signal are unique to each species, especially a combination of the pulse waveform, duration, amplitude, phase and frequency; tiny discharges of just a few millivolts, used for navigation the environment, including locating the bottom-dwelling invertebrates that compose their diets and to send signals between fish of the same species; much more powerful discharges are used to stun prey.
TaxonomyGymnotiformes is thought to be the sister group to the
Siluriformes.
FamiliesSuborder Gymnotoidei
•
Gymnotidae: Banded knifefishes, Electric eel.
Suborder Sternopygoidei
Superfamily Rhamphichthyoidea
• Rhamphichthyidae: Sand knifefishes.
• Hypopomidae: Bluntnose knifefishes.
Superfamily Apteronotoidea
• Sternopygidae: Glass and rat-tail knifefishes.
• Apteronotidae: Ghost knifefishes.