Electroreception

Electroreception, sometimes written as electroception, is the biological ability to receive and make use of electrical impulses. It is much more common among aquatic creatures, as water is a far superior conductor than air. Electroreception is primarily used for electrolocation: the ability to use electric fields to locate objects (compare with animal echolocation).

Mechanism
Many primitive fishes such as sharks, rays, lampreys, bichirs, lungfish, coelacanths, and sturgeons have electroreceptors sense which is believed to be derived from the lateral line sense. Electroreception is absent in most teleost fishes except for the catfishes, the gymnotiform electric fishes and the African mormyriform fishes. The sense operates in two main modalities; active and passive. Active electroreception relies upon tuberous electrororeceptors which are sensitive to high frequency (20-20,000 Hz) stimuli. Passive electrolocation depends upon ampullary receptors which are sensitive to low frequency stimuli (below 50 Hz); Ampullary receptors have a jelly filled canal leading from the sensory receptors to the skin surface while tuberous receptors lack a canal but show a loose plug of epithelial cells which capacitatively couples the sensory receptor cells to the external environment. In mormyrid electric fish from Africa, tuberous receptors known as Knollenorgans function in reception of electric communication signals from conspecifics.

Active
In "active" electroreception, the animal senses its surrounding environment by generating electric fields and detecting distortions in these fields using electroreceptor organs. This ability is especially important in murky water, where visibility is low.

Animals that use active electroreception include the weakly electric fish, which generate small (typically less than one volt) electrical pulses using an organ in the tail consisting of two to five rows of modified muscle cells (electrocytes).

Weakly electric fish can discriminate between objects with different resistance and capacitance values, which may help in identifying the object. They can also communicate by modulating the electrical waveform they generate; an ability known as electrocommunication.

Active electroreception typically has a range of about one body length, though objects with an electrical resistance similar to that of water are nearly undetectable.

Passive
In "passive" electroreception the animal senses the weak bioelectric fields generated by other animals. Animals that use passive electroreception include sharks and rays.

Elasmobranchii
Sharks and rays (members of the subclass Elasmobranchii) rely heavily on electrolocation in the final stages of their attacks, as can be demonstrated by the robust feeding response elicited by electric fields similar to those of their prey. Sharks are the most electrically sensitive animals known; responding to DC fields as low as 5 nV/cm.

The electric field sensors of sharks are called the ampullae of Lorenzini. They consist of electroreceptor cells connected to the seawater by pores on their snouts and other zones of the head. A problem with the early submarine telegraph cables was the damage caused by sharks who sensed the electric fields produced by these cables. It is possible that sharks may use Earth's magnetic field to navigate the oceans using this sense.

A recent study has suggested that the same genes that contribute to a shark's sense of electroreception may also be responsible at least in part to the development of facial structures in humans.

Other vertebrates
The electric eel (a strongly electric fish), besides its ability to generate high voltage electric shocks, uses lower voltage pulses for navigation and prey detection in its turbid habitat. This ability is shared with other Gymnotiformes.

Monotremes (the echidna and platypus) are the most prevalent mammals that use electroception. Among these, the platypus has the most acute sense. The platypus may use electroreception in conjunction with tactile (pressure) sensors in order to determine the distance to prey, by using the delay between the arrival of electrical signals and pressure changes in the water.

There are no known cases of mimicry involving electroreception, though it is theoretically possible.