An electric fish is a fish that can generate electric fields. It is said to be electrogenic; a fish that has the ability to detect electric fields is said to be electroreceptive. All fish that are electrogenic are also electroreceptive. Electric fish species can be found both in the sea and in freshwater rivers of South America and Africa. Many fish such as sharks, rays and catfishes can detect electric fields, and are thus electroreceptive, but as they cannot generate an electric field they are not classified as electric fish. Most common bony fish (teleosts), including most fish kept in aquaria or caught for food, are neither electrogenic nor electroreceptive.
Strongly and weakly electric fish
Electric fish produce their electrical fields from a specialized structure called an electric organ. This is made up of modified muscle or nerve cells, which became specialized for producing bioelectric fields stronger than those that normal nerves or muscles produce. Typically this organ is located in the tail of the electric fish. The electrical output of the organ is called the electric organ discharge (EOD).
Fish that have an EOD that is powerful enough to stun their prey are called strongly electric fish. The amplitude of the signal can range from 10 to 500 Volts with a current of up to 1 Ampere. Typical examples are the electric eel (Electrophorus electricus; not a true eel but a knifefish), the electric catfishes (family Malapteruridae), and electric rays (order Torpediniformes).
By contrast, weakly electric fish generate a discharge that is typically less than one volt in amplitude. These are too weak to stun prey, but are used for navigation, object detection (electrolocation) and communication with other electric fish (electrocommunication). Some of the best known and most studied examples are Peters' elephantnose fish (Gnathonemus petersi) and the black ghost knifefish (Apteronotus albifrons).
The EOD waveform takes two general forms depending on the species. In some species the waveform is continuous and almost sinusoidal (for example the genera Apteronotus, Eigenmannia and Gymnarchus) and these are said to have a wave-type EOD. In other species, the EOD waveform consists of brief pulses separated by longer gaps (for example Gnathonemus, Gymnotus, Raja) and these are said to have a pulse-type EOD.
Table of electric fish
Following is a table of all known electric fish species within fresh water. There are two groups of marine fishes, the electric rays (Torpediniformes: Narcinidae and Torpedinidae) and the stargazers (Perciformes: Uranoscopidae) capable of generating strong electric pulses.
References
- Bullock, T.H., Heiligenberg, W. (eds) (1986) Electroreception. Wiley, 722 pp.
- Heiligenberg, W. (1991) Neural nets in electric fish. MIT Press, 179 pp.
- Moller, P. (1995) Electric Fishes: History and Behavior. Chapman & Hall, 583 pp.
External links
- Electric Fish, Mark E. Nelson, Beckman Institute Neuroscience Program, University of Illinois at Urbana-Champaign, Accessed 11/2006, [1]
- Article at CWRU
- Electric Fish Advertise Their Bodies - Male fish can amp up their electric fields to woo females and intimidate rivals, LiveScience.com, 29 February 2008
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