Wiktor Wise
Fish require oxygen to survive, but instead of lungs, they use gills to extract oxygen from the water. Electric eels are a genus of neotropical freshwater fish from South America that can generate electricity to stun their prey or defend against predators. They were first studied in 1775, and this contributed to the invention of the electric battery in 1800. Electric eels are not closely related to true eels but are members of the electroreceptive knifefish order Gymnotiformes, which also includes the African knifefish. Electric fish have evolved specialized behaviours and can produce electric fields for various purposes, including stunning prey, defence, and signalling.
| Characteristics | Values |
|---|---|
| Diet | Fish, crabs, insects, amphibians, birds, and small mammals |
| Habitat | Streams, rivers, and ponds of the Amazon and Orinoco basins of South America |
| Length | Up to 8 feet (2.5 meters) |
| Weight | Up to 44 pounds (20 kilograms) |
| Electricity Generation | Up to 860 volts |
| Electric Organs | Three separate organs, making up about 80% of the body |
| Electric Charges | Both strong and weak charges used for defense, hunting, communication, and navigation |
| Prey Detection | Motion-sensitive hairs along the body (lateral line system) |
| Prey Stunning | High-voltage pulses (up to 400 per second) to paralyze prey |
| Reproduction | Male creates a bubble nest for female to release eggs |
| Lifespan | Over 20 years in captivity |
| Vision | Poor eyesight |
| Breathing | Obligate air-breathing, surfacing to breathe about every 10 minutes |
| Species | Three species within the genus Electrophorus: Electrophorus electricus and two others |
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What You'll Learn
Electric eels are not true eels but neotropical knifefish
The scientific classification of electric eels is closer to carp and catfish than to true eels. They get their name from their eel-shaped body and their ability to generate an enormous electrical charge to stun prey and deter predators. Their bodies contain electric organs with about 6,000 specialised cells called electrocytes, which store power like tiny batteries. When the eel senses prey or feels threatened, the electrocytes discharge simultaneously, creating an electrical current of up to 600 or 860 volts.
Electric eels are found in the murky streams and ponds of the Amazon and Orinoco basins in South America, where they use their electrolocation abilities to navigate and locate prey. They are one of the few fish species capable of delivering strong electric shocks, which they use to stun their prey. In addition to shocking their prey, electric eels also hunt in packs, herding shoals of fish and launching joint strikes.
The electric eel's ability to generate electricity has inspired the invention of the electric battery and continues to influence advancements in battery technology. However, electric eels are not considered a viable source of renewable energy due to ethical concerns and their intermittent discharge of electricity. Instead, researchers have explored using electric eel tissue to culture biobatteries for storing energy.
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They can deliver shocks of up to 860 volts
Electric eels are the most powerful of all electric fishes, with the ability to generate high-voltage, high-frequency pulses. They can produce shocks of up to 860 volts, which is significantly higher than the previously recorded maximum voltage of about 600-650 volts. This discovery was made by Associate Professor William Crampton, Ph.D., a biologist from UCF, during an expedition to the Tapajós River in Brazil. The species with the new record voltage has been named Electrophorus voltai, after the Italian scientist Alessandro Volta, who invented the electric battery in 1799.
The electric eel's ability to produce such high-voltage shocks is due to the large number of electrocytes available in its body. Electrocytes are modified muscle cells that contain the proteins actin and desmin. In the electric eel's main organ, there are approximately 6,000 electrocytes stacked in series, with 35 such stacks in parallel on each side of the body. This allows the eel to generate a powerful electric current of about 1 ampere.
The electric eel has three pairs of electric organs—the main organ, Hunter's organ, and Sachs' organ—that enable it to generate two types of electric organ discharges: low voltage and high voltage. The main organ and Hunter's organ are rich in the protein calmodulin, which helps regulate the voltage-gated sodium channels that create the electrical discharge. These organs also contain sodium potassium ATPase, an ion pump that creates a potential difference across cell membranes.
The high voltage shocks produced by electric eels are not deadly to humans, but they can be unpleasant. The eels use these shocks for defence against predators and to stun their prey. The strong discharge is produced extremely rapidly, at a rate of up to 500 Hertz, resulting in each shock lasting only about two milliseconds. This quick discharge is made possible by the high number of electrocytes available in the eel's body.
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They use electricity to stun prey and for defence
Electric fish, such as electric eels, electric rays, and stargazers, have organs that can discharge powerful electric currents to stun prey and defend against predators. These organs, composed of electrocytes, allow electric fish to generate high-voltage, low-current discharges in freshwater environments, where power is limited by the voltage needed to drive the current through the high-resistance medium. The electric eel, for example, can deliver shocks of up to 860 volts, exceeding the pain threshold of many species.
Electric eels have three electric organs that produce two types of discharges: those for electrolocation and those for stunning prey. They can generate high-voltage, high-frequency pulses, enabling them to rapidly electrolocate moving prey. The electric eel can also curl up and make contact with its prey at two points along its body to concentrate the electric discharge and more effectively stun its target. Additionally, it has been suggested that electric eels can manipulate the nervous systems and muscles of their prey through electrical pulses, preventing escape or forcing movement to facilitate detection.
Electric rays, similarly, use their electric organs to stun prey before capturing them. They lie in wait for their prey beneath the sand or other substrates. The voltage of electric rays varies, with some species capable of delivering shocks ranging from 8 volts to 220 volts.
In addition to stunning prey, electric fish use their electric discharges for defence against predators. Electric eels, for instance, have been observed leaping out of the water to deliver electric shocks to potential threats. The bluntnose knifefish has evolved to produce an electric discharge pattern similar to the more dangerous electric eel, likely serving as a form of Batesian mimicry to deter predators.
The ability to generate electric fields for stunning prey and defence is not limited to strongly electric fish. Some fish, like the knifefishes and elephantfishes, generate weak electric fields for electrolocation and prey detection. These weakly electric fish can also use their electric discharges for communication, attracting mates, and territorial displays.
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Electric organs have evolved eight times
Electric fish produce their electrical fields from these electric organs, which are made up of modified muscle or nerve cells, specialised for producing strong electric fields. Electric organ discharges vary by species and function, with two types: pulse and wave. Electric fish have evolved many specialised behaviours, with some species eavesdropping on the weak electric signals of their prey to locate them, and some producing electric signals that are harder to detect.
The electric organ evolved from a quirk of fish genetics, with all fish having duplicate versions of the sodium channel gene that produces tiny muscle switches. To evolve electric organs, electric fish turned off one duplicate of the gene in muscles and turned it on in other cells, repurposing the tiny switches that make muscles contract to generate electric signals. Electric organs are larger than muscle fibres, and their functional asymmetry allows for the summation of voltages, much like batteries in a flashlight.
Electric eels, a genus of neotropical freshwater fish from South America, are perhaps the most famous example of electric fish. They are known for their ability to stun prey and deter predators with electrical shocks of up to 860 volts. They have very poor eyesight and rely on their electrolocation abilities to navigate the murky backwaters of the Amazon and Orinoco rivers.
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Gills are efficient at extracting oxygen from water
Gills are organs that allow fish to extract oxygen from water. They lie behind and to the side of the mouth cavity and consist of fleshy filaments supported by gill arches and filled with blood vessels, giving them a bright red colour. Gills have a very high surface area, which is necessary given the low concentration of oxygen in water.
Gills work in a similar way to lungs. As a fish opens its mouth, it pulls in oxygen-rich water, which it then pumps over its gills. The capillaries in the gills then pick up the oxygen from the water, and the blood moves through the fish’s body to deliver the oxygen, just as in humans. The gills then push the oxygen-poor water out through openings in the sides of the pharynx. This process is known as counter-current exchange.
The high surface area of gills is achieved through their structure. They are like a slightly opened book with many pages, with the front and back of each page able to extract oxygen from the water passing through. The water between the pages and the weightlessness of being underwater help to keep the pages from sticking together.
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Frequently asked questions
Fish use gills to breathe. Gills are branching organs located on the side of a fish's head that contain many small blood vessels called capillaries. As the fish opens its mouth, water runs over the gills, and blood in the capillaries picks up oxygen that's dissolved in the water.
Electric eels generate electricity through an electric organ. This organ is made up of electrocytes, modified muscle or nerve cells, specialized for producing strong electric fields.
Electric eels use electricity to stun their prey, delivering shocks of up to 860 volts. They can also use electricity to defend against predators and for signalling in courtship.
Fish can survive electric eels by avoiding them. Electric eels are nocturnal and have poor vision, so fish can potentially avoid them during the day. Additionally, electric eels are freshwater fish, so marine fish are not at risk.
