Evolution and Systematics
Functional Adaptations
Functional adaptation
Electric organs in mormyrid and knifefish gymnotids aid navigation by creating an electric force field around the fish.
"Two other fish, the mormyrids and the knifefish gymnotids, use their electric organs to navigate. These organs create an electric force field that surrounds the fish as it swims, and is modified by the relative conductivity of objects in the fish's immediate surroundings. The fish detects and interprets these electrical fluctuations through electroreceptors embedded in its body, so that it has a constantly changing electrical image that enables it not only to navigate effectively around obstacles in even the darkest water but also to sense nearby prey, and anything else coming its way." (Shuker 2001: 53-54)
Learn more about this functional adaptation.
- Shuker, KPN. 2001. The Hidden Powers of Animals: Uncovering the Secrets of Nature. London: Marshall Editions Ltd. 240 p.
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Naked-back knifefish
The naked-back knifefishes are a family (Gymnotidae) of knifefishes (knivefish) that are found only in fresh waters of Central America and South America.[1] All have organs adapted to the exploitation of bioelectricity. The family has 33 valid species in two genera.[2] There are a number of undescribed species known in museum collections.
These fish are nocturnal and mostly occur in quiet waters from deep rivers to swamps. In strongly-flowing waters they may bury themselves.[1]
Physical characteristics
Like the other gymnotiforms, Gymnotids have a classic knifefish body. The body is long and eel-like, the dorsal fin and pectoral fins are absent, and the anal fin is extremely long and used for movement.[1]
The sole member of Electrophorus is the electric eel, which produces both strong (up to 600 volts) and weak (<1 V) electric discharges, for use in predation and communication/navigation, respectively. The electric eel is the largest of the gymnotiform fishes, growing up to more than 2 metres (6.6 ft) length. Species of Gymnotus reach up to about 100 centimetres (3.3 ft) in length.[2]
Genera
There are 37 species in two genera:[3]
References
- ^ a b c Froese, Rainer, and Daniel Pauly, eds. (2007). "Gymnotidae" in FishBase. Apr 2007 version.
- ^ a b Nelson, Joseph, S. (2006). Fishes of the World. John Wiley & Sons, Inc.. ISBN 0-471-25031-7.
- ^ Froese, Rainer, and Daniel Pauly, eds. (2011). "Gymnotidae" in FishBase. December 2011 version.
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