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 Features

 

The  electric eel seems to have adapted and evolved to its preferred environment.  It is able to swim forward and backward with its undulating anal fin.  This allows it a better sense of its surroundings. The muddy waters it inhabits contain extremely low oxygen levels.        The fish frequently surfaces and ‘gulps’ 80% of its oxygen through its practically toothless, yet heavily vasculated mouth. The gills filter the remaining 20% of its oxygen intake.  An electric eel will die if left in water for more than 20 minutes.
The cloudy water also does not create visual obstacles for the fish either.  Not only is the electric eel nocturnal, a fully grown fish can hardly use their beady eyes.  Although the youth can see, the adults become increasingly blind due to the constant exposure to the generated electrical field.  In fact, the world of the electric eel is entirely electrical.

By producing an electrical current with low-voltage, the electric eel creates an electrical field, which surrounds their elongated bodies. This enables it to navigate and communicate.  Electric fish like the  electric eel are generally divided into two categories:  Strongly electric fish and Weakly electric fish.   Strongly electric fish are distinguished by a pulsated-like discharge, as opposed to the Weakly electric fish, with a  wavelike discharge.

These  discharges are called electric organ discharge (EOD). Strongly electric fish use electric organ discharge to stun prey in addition to navigation, object detection (electrolocation) and communication (electrocommunication.)

Of the Strongly electric fish, the electric eel is set apart.  No other electric animal compares to the electric eel’s unique ability to generate such an enormous amount of electricity for a predatory and territorial weapon.  A fully grown eel can produce a potential difference of 600 volts (five times an electrical outlet).  In contrast, another Strongly electric fish, the torpedo ray, can only discharge approximately half the voltage of the Electrophorus Electricus.

When the electric eel shocks its prey, it either stuns and paralyzes it or kills  it.  This would be evolutionarily beneficial to the toothless fish so that the prey does not present a struggle to its predator. The electric eel also shocks itself in the process, yet tolerates the current.  Its place in the electrical current flow decreases the effects of the shock, as does its thick, course skin.

This extraordinary ability has naturally drawn a great deal of attention as to how electrical generation of this magnitude occurs within a single animal.  Here we’ll explore the underlying mechanisms of the electrical discharge that set electric eels apart from all other animals.

 

Electric Organs and Electrocytes

The vital organs of the electric eel are located entirely in the first 1/5 of its body, leaving the remaining 4/5 tail occupied by three electric organs.

 The Sachs’ organ is where low-voltage pulses are emitted  for electrolocation and navigation.

The Hunter and Main organs are where the high-voltage emission occurs.

Electric organs are made up of cells called Electrocytes.  Some scientists believe these cells are derivative of a muscle-cell since nerve cells synapse onto them and they behave much like a muscle-cell post-synaptically.  However, they are unlike muscle cells in that they don’t contract.  Flat and disk-like, the electrocytes are stacked in a sequence much like a dry-cell battery, with the head as the positive pole and the tail as the negative pole.  Each electrocyte generates .15 volts, which is a very small amount.  However, when 4,000 electrocytes are lined up generating electricity at the exact same time at .15 volts each, the shock equals at least 600 volts, which can paralyze or kill a human, especially after repeated shocks.

At rest, the Na+K+ pump, concentration and electrical gradient keeps the inside of the electrocyte at a resting potential of .08 volt.  When the electric eel electrolocates its prey, the brain sends a signal through the nervous system to the electric organs.  Acetylcholine is dropped onto the electrocyte which binds to the corresponding receptor on the  ion.  This opens the ion channels of the cell, allowing Na+ to rush in.  The cell then depolarizes, momentarily reversing the charge, and fires.

Since the electrocytes are lined up, current flows through like a battery, emitting a charge.  However, they must all discharge at the same time.  The electric eel’s design resolves this at the neuronal connections by delaying the signals and action potentials. The closer connections have longer and thinner pathways, which decelerates the signal and allows all electrocytes to synchronize their discharge.