Electrophorus electricus, more commonly known as the electric eel, occupies the northeastern portions of South America. This includes the Guyanas and Orinoco Rivers as well as the middle and lower Amazon basin.
E. electricus dwell mainly on the muddy bottoms of rivers and occasionally swamps, prefering deeply shaded areas. However, they must surface rather frequently because they are air breathers, gaining up to 80 percent of their oxygen through this method. This feature allows E. electricus to survive comfortably in water that has a very low concentration of dissolved oxygen.
Electric eels are not really eels, they are actually ostariophysians, but have a strong physical resemblance to true eels. The body is long and snake-like, lacking caudal, dorsal and pelvic fins. Body length can be as long as 2.5 m. They also have an extremely elongated anal fin, which is used as a means of locomotion. It is cylindrical in shape with a slightly flattened head and large mouth. The vital organs to the fish are all in the anterior portion of the body and only take up about 20 percent of the fish. The posterior portion of the body contains the electrical organs. They do have gills, though it is not their primary source of oxygen intake. Electric eels are obligatory air breathers. They receive almost 80 percent of their oxygen through their highly vascularized mouth. A thick, slimy skin covers the entire body of E. electricus. The skin is used as a protective layer, often from their own electrical current that is produced. Electric eels range from gray to brownish/black in color with some yellowish coloration on the anterior ventral portion of the body.
(Riis- Johannessen, 2001; Berra, 2001; Val and de Almeida-Val, 1995)
The development of electric organs in E. electricus happens very soon after birth. There has been evidence that fish as small as 15 mm have begun electrical organ development. This initial growthof a weak electrical organ allows for orientation. Strong electric organs do not develop until the fish is approximately 40 mm. Observations have shown small juveniles surrounding the head of the parent; this is most likely before the young develop their own orientation organs.
(Brown, 1957; Moller, 1995; Berra, 2001)
Electric eels reproduce during the dry season. The eggs are deposited in a well-hidden nest made of saliva, built by the male. In field observations, an average of 1200 embryos were hatched. Fecundity counts have been documented as high as 17,000 eggs. The electric eel is thought to be a fractional spawner.
Males will defend their nest and the fry vigorously.
The lifespan of electric eels in the wild is unknown. In captivity males live between 10 and 15 years, while females usually survive between 12 and 22 years.
Although electric eels have the potential to be fairly aggressive animals, they are not. They really only use their strong electric organ discharges for predation and defensive purposes. Weak electric organ discharges are used for electrolocation as well as identification of foreign objects. This is especially important because of their poor eyesight. They are nocturnal animals that live in muddy dark waters, so they must rely on electricity for sensing. Electric eels tend to stay relatively rigid in order to fully use their electrical capabilities. They have a positive charge near the head, while the tail end is negative. When scanning their environment with electric current, they begin at the tail and finish with the head. In order to do this the fish must be able to swim backward. The polarity of the fish itself helps to create this electric field that dictates much of the animal’s behavior.
The use of electrical organs has been studied in great detail. From many different experimental situations it is clear that the eels are able to detect an electrical circuit in the water and differentiate between a closed and an open system. It has also been determined that electric eels are very sensitive to the changes in water conductivity. It is the electroreception system that allows them to navigate through the muddy dark waters they dwell in.
(Moller, 1995; Berra, 2001; Riis-Johannessen, 2001)
The Sachs organ is the primary source of communication among E. electricus. This organ transmits a weak signal, only about 10V in amplitude. These signals are used in communication as well as orientation, useful not only to find prey but also thought to play an important role in finding and choosing a mate.
Scientists have been able to determine through experimental information that E. electricus has a well developed sense of sound. They have a Weberian apparatus that connects the ear to the swim bladder which greatly enhances their hearing capability.
(Berra, 2001; Brown, 1957; Moller, 1995)
To find prey E. electricus uses its weak electric organ, also known as the Sachs organ. This transmits a weak pulsating signal, thought to be used for locating and directional purposes. Once prey is found the electric eel will use a much larger electrical current to stun the fish. This is done with the two larger electric organs, the Main and Hunters organs. The shock itself does not kill the prey, but it is usually sufficiently stunned. Since eels lack maxilla teeth, it is difficult to eat a fish that is thrashing about. However, since the prey is fairly stationary eels are able to open their mouths to create a suction, which allows them to eat the prey with ease. Most adult electric eels will feed on smaller fish, while juveniles will prey mainly on smaller invertebrates.
(Berra, 2001; Riis-Johannessen, 2001)
Predation of electric eels is usually prevented by their electric shocking capabilities. They can produce voltage as high as 650 volts. Although this shock is rarely deadly it is enough to deter most predators. These defensive electrical pulses are created by two organs in E. electricus, the Main and Hunters organs. It is the strength of these two organs and the electric eels pulsating electric current that classifies it as a strongly electric fish.
(Berra, 2001; Brown, 1957)
E. electricus have very little economic value to humans. Occasionally they are eaten by locals of the Amazon area; however they are commonly avoided due to the electrical shocks that can be given out up to eight hours after death. Although there is no commercial value, the electric eel has been a constant source of study for many years. The scientific community is very interested in studying the electrical capabilities of these fish. Of electric fish, E. electricus is the best documented species.
Electric eels can be very dangerous to humans because of their strong electric capabilities. They are able to produce enough voltage to severely injure humans and other animals.
William Fink (editor), University of Michigan-Ann Arbor.
Traci Valasco (author), University of Michigan-Ann Arbor.
living in the southern part of the New World. In other words, Central and South America.
uses sound to communicate
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
an animal that mainly eats meat
uses smells or other chemicals to communicate
uses electric signals to communicate
fertilization takes place outside the female's body
union of egg and spermatozoan
mainly lives in water that is not salty.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
parental care is carried out by males
having the capacity to move from one place to another.
specialized for swimming
the area in which the animal is naturally found, the region in which it is endemic.
active during the night
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
an animal that mainly eats fish
breeding is confined to a particular season
reproduction that includes combining the genetic contribution of two individuals, a male and a female
a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.
uses touch to communicate
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
Berra, T. 2001. Freshwater Fish Distribution. San Diego: Academic Press.
Cormier, L. 2000. "More Information about Electric Eels" (On-line). Accessed November 10, 2002 at http://whozoo.org/Intro2000/tashcorm/tempagetwo.htm.
Keynes, R. 1957. Electric Organs. Pp. 323-343 in M Brown, ed. The Physiology of Fishes, Volume II. New York: Academic Press, Inc..
Moller, P. 1995. Electric Fishes: History and Behavior. New York: Chapman & Hall.
Riis-Johannessen, T. 2001. "The Electric Eel" (On-line). Accessed Oct. 30, 2002 at http://www.chm.bris.ac.uk/webprojects2001/riis/electriceels.htm.
Val, A., M. de Almeida - Val. 1995. Fishes of the Amazon and their Environment: Physiological and Biochemical Aspect. New York: Springer.