The Electric Eel

Get a Charge (or Not) Out of Zoo Miami’s Electric Eel

By Susana Cortázar

Okay, so they’re not “real” eels, are not even in the eel family but rather the knife fish family, but because of their tubular shape, they are commonly called eels.  What makes them different from the real McCoy?  Several factors such as their need to breathe air to get 80% of their oxygen instead of absorbing it through gills, their lack of teeth and “sucking up” their prey much like a vacuum cleaner does, their dorsal fin, the fact they are a freshwater species, and most important, their production of electricity which can cause quite a bit of damage to animals and humans. 

Electric eels are native to the shaded rivers and muddy waters of the middle and lower Amazon River Basin in South America, and the Orinoco River and its tributaries. They like murky waters because of their high sediment loads, grow between six to eight feet in length and can weigh up to 45 pounds. Their status is common. Their diet consists of larvae, worms and insects.  Young electric eels eat invertebrates such as freshwater worms and shrimp that are size-appropriate for them.

Visitors to Zoo Miami can see our electric eel in the Amazon and Beyond’s Flooded Forest. It has not been sexed and measures four feet long.  As nocturnal animals, they are relatively inactive during the day, although Zoo Miami’s has “slightly altered its behavior and become active in response to movement around its tank from patrons and its feeding schedule,” according to one  of its zookeepers, Andrea Perleberg.
 

Electric eels have an interesting reproductive pattern.  Females lay eggs in a nest of saliva built by the male, who will stay around to protect the eggs from predators.  Approximately 1,200 embryos hatch and the male continues to protect the fry as well.  As eels do not have a highly developed sense of sight, they start discharging electric signals from a very young age in order to “get their bearings, communicate with each other, and paralyze their prey long enough to eat it,” according to Andrea.

Electric eels possess three organs which produce electricity.  The Sachs organ, located near the head, produces the weak electric charge used to communicate and orient themselves to their environment. The Main and Hunter’s organs produce the much stronger electric charge used to stun and paralyze their prey.  And since they are electricity-producing fish, their bodies are like a battery – the head is positive and the tail is negative. Only 20% of their body consists of vital organs and the remaining 80% is devoted to the electricity-producing ones.
 

One of the most distinguishing features of the electric eel is its Weberian apparatus, which consists of four pairs of bones at the vertebrae by the skull.   Zoo Miami Curator of Ectotherms Nicole Atteberry explains how this apparatus works.  “The four pairs of bones connect the eel’s swim bladder and inner ear, thereby allowing external pressure changes such as sound waves to travel from the eel’s swim bladder to the inner ear.  In other words, it serves as a sound conductor for the eel.”

Depending on their severity, which can be up to 650 volts, electric eel discharges can cause serious injury to humans and even cardiac or respiratory failure if shocks are consistently repeated.  Human deaths usually occur when the animal stuns the person and he/she drowns as a result. 

According to Andrea, “we keepers have to be very careful when we handle the electric eel or do any maintenance in the tank as we run the risk of being shocked.  We wear gloves and use non-conductive equipment like nets, feeding tongs, and algae scrubbers so the electric current is not able to pass through.”  Adds Andrea, “electric eels are trainable.  A friend of mine was able to target- train the five-foot long electric eel we had at the zoo where I used to work. She used a plastic bottle on a stick with rocks inside and used the vibrations as a target. The eel would come over, touch the target, and remain still until it was rewarded for its behavior with a fish.”

Reader beware: even if you should come across a dead electric eel, be very careful because it can produce post-mortem discharges, so please don’t take any chances should you run into one. 

But since Zoo Miami’s electric eel is happily ensconced in its tank, make sure you come see it without worrying about getting a charge out of it.