Each animal that hunts for its food depends upon definite cues in the search. For this they develop special adaptations which help to increase biotic potential. Although almost any individual kind of animal demonstrates such adaptations in sensory mechanisms related to food acquisition, some are sufficiently spectacular to earn special mention.
One such is the sensory adaptations found in certain members of Teleost fishes, which have independently developed organs, which produce electricity. These are used for defense, the capture of prey and perhaps as direction finders.
The best-known is the so called Electric `eel' (Electrophorus) — a blind, superficially eel-like fish which grows to a length of about eight feet, and is almost as thick as a man's thigh and lives in shallow muddy parts of the Amazon and other South American rivers.
On land Electrophorus can discharge about 500 volts. In water the charge is partly short circuited and the shock is about 250 volts, but still sufficiently strong to cause great discomfort to man or to activate an electric buzzer.
The electric organ consists of some seventy columns, each of which contain a series of about 600 disc-shaped syncytial electroplaxes (Electroplate cells). The cells are probably formed from striated muscle-cells and together constitute a jelly like mass located in the postero-ventral four-fifth of the body and tail.
Each electroplate is innervated and shocks are normally transmitted only when the fish is molested or when it comes within the range of its prey, which is stunned and then swallowed whole.
These fishes that can generate high voltages have protective insulation around their own nervous system, shielding them from damage.
Source : The Hindu
