No electrocution with electroreception

Everyone knows that electricity and water don’t mix. Nevertheless, in some cases (not so rare), amazing adaptations show us the contrary. About 250 electric species inhabit the underwater world, especially in cartilaginous fishes as sharks and rays.

Electric fields:

Abiotics : They are electric fields at low frequences, due to geochemical or oceanographic processes. Indeed, water flows can interfer with the terrestrial magnetic field. They can also reach high frequencies when they are caused by magnetic storms or strong sismic activities. This fluctuating signals are thus perceived as perturbations per organisms.
Biotics : They are generated by biochemical operations of living organisms. Epitheliums have an electric potential and are electric sources. They can be high frequence signals when generated by specialized organ, often muscular or neuro-muscular. Electric shock can be brief or more or less continous. These signals allow active electrolocation and electrocommunication.
Electro-receiver

Ampullary organ : Ampullae of Lorenzini are present within every electroreceptive organism, and answer to low frequence signals (?50 Hz). Sensibility can be very high but each ampullae has a lower detection potential around 2?V/cm. Ampullae contains a jelly rich in ions to transfer electric information, its resistance is equal to sea water resistance. Cells that recover the canal are more resistant, whereby the canal is like an electric cable connecting cellular-receptors to sea water. According to electrical environment, there is neurotransmitter release at the basal part of electroreceptive cells and nervous cells stimulation or there is inhibition of this stimulation. Ampullae have a directional sensibility and deduce where the electric signal comes from.

Tuberous organ : Capsules are below epiderm. They are part of a system that combines electroreception (with electric shock organs for electrocommunication) and active electrolocation (cellular receptors at high frequencies and limited to species that produce their own signals). Tuberous organ respond to high frequencies (50 to 200 Hz). Frequencies are fixed from the frequency of discharge issued by the animal. Tuberous organ detect the moment of emission of the discharge and otherwise detect amplitude of the discharge. This allow organisms to distinguish their own emissions from those of their congeners.

Biological functions:

Passive electrolocation : It consists in detecting electric fields not produced by the organism itself, but from a prey, or bounced on a mineral structure, or magnetic fields from the environment.
-> Detection of prey and orientation in space.
Signals produced by congeners can also be used while reproductive period. Silurifom fishes use passive electrolocation to locate prey, for instance Clarias batrachus below.

VIDEO: http://www.youtube.com/watch?v=K-f8nIBRktA