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)
Communication Channels: acoustic ; electric
Perception Channels: tactile ; chemical
IUCN Red List of Threatened Species: least concern
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 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.
(Cormier, 2000)
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.
(Moller, 1995)
Positive Impacts: research and education
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)
Primary Diet: carnivore (Piscivore , Eats non-insect arthropods)
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.
(Berra, 2001)
Biogeographic Regions: neotropical (Native )
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.
(Riis-Johannessen, 2001)
Habitat Regions: tropical ; freshwater
Aquatic Biomes: rivers and streams
Wetlands: swamp
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.
(Cormier, 2000)
Typical lifespan
Status: captivity: 10 to 22 years.
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)
Range mass: 20 (high) kg.
Range length: 2.5 (high) m.
Other Physical Features: bilateral symmetry
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)
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.
(Moller, 1995)
Breeding season: dry season
Average number of offspring: 1200.
Key Reproductive Features: iteroparous ; seasonal breeding ; sexual ; fertilization (External ); oviparous
Males will defend their nest and the fry vigorously.
Parental Investment: male parental care
Electric Eels (Electrophorus electricus) are large gymnotiform fish that may exceed 2 m in length and live in northern South America in the Amazon and Orinoco River basins and other areas in northern Brazil (the species can be found in Brazil, French Guiana, Guyana, Peru, Suriname, and Venezuela) (Eschmeyer 2012). These fish are famous for their ability to emit powerful electrical discharges, which are used both in predation and defense, of more than 500 volts (weaker electric fields are generated to gather information about the fish's surroundings). Depending on circumstances, the shock generated is potentially strong enough to pose a serious danger even to a large animal such as a human. Although musing about the electrical potential of this fish may simply alarm some people, others have been inspired to think about harnessing this power for fun, education, or more, as seen in this video about Electric Eel power in a Japanese Christmas display (which has been extended to include a human visitor-powered Santa Claus).
Electric Eels are mouth-breathers and will drown if denied access to air. The oral cavity is highly vascularized and folded to increase surface area, facilitating gas exchange. Air is taken in every few seconds to every few minutes. In addition to gas exchange in the oral cavity, carbon dioxide apparently escapes through the relatively permeable skin.
Electrophorus electricus is the best-known species of electric eel. It is a South American electric fish. Until the discovery of two additional species in 2019, the genus was classified as the monotypic, with this species the only one in the genus.[2] Despite the name, it is not an eel, but rather a knifefish.[3] It is considered as a freshwater teleost which contains an electrogenic tissue that produces electric discharges.[4]
The species has been reclassified several times. When originally described by Carl Linnaeus in 1766, he used the name Gymnotus electricus, placing it in the same genus as Gymnotus carapo (banded knifefish) which he had described several years earlier. It was only about a century later, in 1864, that the electric eel was moved to its own genus Electrophorus by Theodore Gill.[5]
In September 2019, David de Santana et al. suggested the division of the genus into three species based on DNA divergence, ecology and habitat, anatomy and physiology, and electrical ability: E. electricus, E. voltai sp. nov., and E. varii sp. nov. The study found E. electricus to be the sister species to E. voltai, with both species diverging during the Pliocene.[2]
E. electricus has an elongated, cylindrical body, typically growing to about 2 m (6 ft 7 in) in length, and 20 kg (44 lb) in weight, making them the largest of the Gymnotiformes.[6] Their coloration is dark gray-brown on the back and yellow or orange on the belly. Mature females have a darker abdomen. They have no scales. The mouth is square and positioned at the end of the snout. The anal fin extends the length of the body to the tip of the tail. As in other ostariophysan fishes, the swim bladder has two chambers. The anterior chamber is connected to the inner ear by a series of small bones derived from neck vertebrae called the Weberian apparatus, which greatly enhances its hearing capability. The posterior chamber extends along the whole length of the body and maintains the fish's buoyancy.
E. electricus has a vascularized respiratory system with gas exchange occurring through epithelial tissue in its buccal cavity.[7] As obligate air-breathers, E. electricus must rise to the surface every ten minutes or so to inhale before returning to the bottom. Nearly eighty percent of the oxygen used by the fish is obtained in this way.[8]
E. electricus has three pairs of abdominal organs that produce electricity: the main organ, Hunter's organ, and Sachs' organ. These organs occupy a large part of its body, and give the electric eel the ability to generate two types of electric organ discharges: low voltage and high voltage. These organs are made of electrocytes, lined up so a current of ions can flow through them and stacked so each one adds to a potential difference.[9] The three electrical organs are developed from muscle and exhibit several biochemical properties and morphological features of the muscle sarcolemma; they are found symmetrically along both sides of the eel.[4]
When the eel finds its prey, the brain sends a signal through the nervous system to the electrocytes. This opens the ion channels, allowing sodium to flow through, reversing the polarity momentarily. By causing a sudden difference in electric potential, it generates an electric current in a manner similar to a battery, in which stacked plates each produce an electric potential difference.[9] Electric eels are also capable of controlling their prey's nervous systems with their electrical abilities; by controlling their victim's nervous system and muscles via electrical pulses, they can keep prey from escaping or force it to move so they can locate its position.[10][11]
Electric eels use electricity in multiple ways. Low voltages are used to sense the surrounding environment. High voltages are used to detect prey and, separately, stun them, at which point the electric eel applies a suction-feeding bite.[12]
Sachs' organ is associated with electrolocation. Inside the organ are many muscle-like cells, called electrocytes. Each cell produces 0.15 V, the cells being stacked in series to enable the organ to generate nearly 10 V at around 25 Hz in frequency. These signals are emitted by the main organ; Hunter's organ can emit signals at rates of several hundred hertz.[13]
There are several physiological differences among the three electric organs, which allow them to have very different functions. The main electrical organ and the strong-voltage section of Hunter's organ are rich in calmodulin, a protein that is involved in high-voltage production.[14] Additionally, the three organs have varying amounts of Na+/K+-ATPase, which is a Na+/K+ ion pump that is crucial in the formation of voltage. The main and Hunter’s organs have a high expression of this protein, giving it a high sensitivity to changes in ion concentration, whereas Sachs' organ has a low expression of this protein.[15]
The typical output is sufficient to stun or deter virtually any animal. The eels can vary the intensity of the electric discharge, using lower discharges for hunting and higher intensities for stunning prey or defending themselves. They can also concentrate the discharge by curling up and making contact at two points along its body.[16] When agitated, they can produce these intermittent electric shocks over at least an hour without tiring.
E. electricus also possesses high frequency–sensitive tuberous receptors, which are distributed in patches over its body. This feature is apparently useful for hunting other Gymnotiformes.[13] E. electricus has been prominent in the study of bioelectricity since the 18th century.[17] The species is of some interest to researchers, who make use of its acetylcholinesterase and adenosine triphosphate.[18][19]
Despite being the first described species in the genus and thus the most famous example, E. electricus actually has the weakest maximum voltage of the three species in the genus, at only 480 volts (as opposed to 572 volts in E. varii and 860 volts in E. voltai).[2]
E. electricus is restricted to freshwater habitats in the Guiana Shield. Populations in the Amazon basin, Brazilian Shield, and other parts of the Guiana Shield are now thought to belong to E. varii and E. voltai.[20]
E. electricus feeds on invertebrates, although adult eels may also consume fish and small mammals, such as rats. First-born hatchlings eat other eggs and embryos from later clutches.[13] The juveniles eat invertebrates, such as shrimp and crabs.
E. electricus is known for its unusual breeding behavior. In the dry season, a male eel makes a nest from his saliva into which the female lays her eggs. As many as 3,000 young hatch from the eggs in one nest. Males grow to be larger than females[21][22] by about 35 cm (14 in).[23]
Electrophorus electricus is the best-known species of electric eel. It is a South American electric fish. Until the discovery of two additional species in 2019, the genus was classified as the monotypic, with this species the only one in the genus. Despite the name, it is not an eel, but rather a knifefish. It is considered as a freshwater teleost which contains an electrogenic tissue that produces electric discharges.
