Gymnotiformes
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The Gymnotiformes is a lineage of ostariophysan teleost electric fishes. Common names found in the literature include the Neotropical electric fishes, South American electric fishes, or American knifefishes. They are primarily freshwater inhabitants and have organs adapted to the generation of electric fields.
The best-known species is the electric eel (Electrophorus electricus) which uses powerful electric shocks (up to 600 V) for hunting and self-defense. Other species familiar in the aquarium trade are: the black ghost knifefish (Apteronotus albifrons), the glass knifefish (Eigenmannia virescens), and the banded knifefish Gymnotus carapo.
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[edit] Taxonomy
There are currently about 134 known species over 30 genera contained in 5 families, though at least 38 or so additional species are yet to be formally described.[1] The actual number of species in the wild is unknown.
This group is thought to be the sister group to the Siluriformes.[1]
The families are classified over suborders and superfamilies as below.[1]
Order Gymnotiformes
- Suborder Gymnotoidei
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- Family Gymnotidae (nakedback knifefishes and electric eel)
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- Suborder Sternopygoidei
- Superfamily Rhamphichthyoidea
- Family Rhamphichthyidae (sand knifefishes)
- Family Hypopomidae (bluntnose knifefishes)
- Superfamily Apteronotoidea
- Family Sternopygidae (glass knifefishes)
- Family Apteronotidae (ghost knifefishes)
- Superfamily Rhamphichthyoidea
[edit] Distribution and habitat
Gymnotiform fishes inhabit freshwater rivers and streams throughout the humid Neotropics, ranging from Guatemala to Northern Argentina. They are nocturnal fishes.
[edit] Physical characteristics
Gymnotiformes have a knife-shaped, eel-like body that is either compressed or cylindrical. They lack pelvic fins and dorsal fins. The anal fin is extremely long; this fin is undulated to allow the fish to move both forwards and backwards. The caudal fin is absent or, in the apteronotids, greatly reduced. The gill opening is restricted. The anal opening is under the head or the pectorals.[1]
These fish possess electric organs that allow them to produce electricity. In most Gymnotiforms, the electric organs are derived from muscle cells. However, in adult apteronotids they are derived from nerve cells.[1] All gymnotiform species generate weak (<1 V) electric fields, using them for navigation and communication. The electric discharge is continuous, being generated day and night throughout the entire life of the individual. Certain aspects of the electric signal are unique to each species.[citation needed]
[edit] See also
[edit] References
- ^ a b c d e Nelson, Joseph, S. (2006). Fishes of the World. John Wiley & Sons, Inc.. ISBN 0471250317.
