VII.2 Electric Fields and Electroreception:
How Electrosensory Fish Perceive
Their Environment
Gerhard von der Emde
Institut flir Zoologie, Universitat Bonn, Poppelsdorfer Schloss, 53115 Bonn,
Germany
Abstract
The electrosensory system of fishes is well matched to the conditions of the
aquatic habitat, where electrical fields of biotic or abiotic sources are abundant.
During passive electrolocation environmental low-frequency electrical fields are
detected for orientation, navigation and prey detection. Weakly electric fish have
perfected electro-orientation by developing active electrolocation. They actively
emit high-frequency electrical signals with specialized electric organs. Objects are
located by sensing the specific distortions they evoke on the electrical field which
builds up during each electric organ discharge. The production of their own
electric signals makes weakly electric fish independent of existing electrical fields
and enables them to actively probe their environment. Several unique adaptations
of the electrosensory system provide the means to detect and localize objects
three-dimensionally in space and to analyze their electrical properties. The
advantage of perceiving an electrically "colorful" picture of their surroundings led
South American and African electric fishes to evolve capacitance detection, i.e.,
the ability to perceive capacitive object properties. Even though the fishes' sensory
capabilities, which are the results of a convergent evolutionary process, look
almost identical, South American and African fishes employ different receptor
types and different neural algorithms to achieve them.
Key words Orientation, object detection, object properties, depth perception,
weakly electric fish
1 Electric Fields in the Aquatic Environment
Animals use sensory signals of various modalities when gathering information
about their environment. Besides visual signals, which play a dominant role in the
sensory life of many species (including humans), signals of other physical
qualities, such as acoustical, mechanical, chemical, and magnetic are also
perceived. Furthermore, several fish species can sense electrical fields which are
How Electrosensory Fish Perceive
Their Environment
Gerhard von der Emde
Institut flir Zoologie, Universitat Bonn, Poppelsdorfer Schloss, 53115 Bonn,
Germany
Abstract
The electrosensory system of fishes is well matched to the conditions of the
aquatic habitat, where electrical fields of biotic or abiotic sources are abundant.
During passive electrolocation environmental low-frequency electrical fields are
detected for orientation, navigation and prey detection. Weakly electric fish have
perfected electro-orientation by developing active electrolocation. They actively
emit high-frequency electrical signals with specialized electric organs. Objects are
located by sensing the specific distortions they evoke on the electrical field which
builds up during each electric organ discharge. The production of their own
electric signals makes weakly electric fish independent of existing electrical fields
and enables them to actively probe their environment. Several unique adaptations
of the electrosensory system provide the means to detect and localize objects
three-dimensionally in space and to analyze their electrical properties. The
advantage of perceiving an electrically "colorful" picture of their surroundings led
South American and African electric fishes to evolve capacitance detection, i.e.,
the ability to perceive capacitive object properties. Even though the fishes' sensory
capabilities, which are the results of a convergent evolutionary process, look
almost identical, South American and African fishes employ different receptor
types and different neural algorithms to achieve them.
Key words Orientation, object detection, object properties, depth perception,
weakly electric fish
1 Electric Fields in the Aquatic Environment
Animals use sensory signals of various modalities when gathering information
about their environment. Besides visual signals, which play a dominant role in the
sensory life of many species (including humans), signals of other physical
qualities, such as acoustical, mechanical, chemical, and magnetic are also
perceived. Furthermore, several fish species can sense electrical fields which are