Electric Eel

Family: Gymnotidae

Electrophorus electricus

Photo © Animal-World: Courtesy Clarice Brough

The Electric Eel creates electricity, making it one of the most amazing creations of nature!

The Electric Eel Electrophorus electricus is one of several species of fish that possess organs that can produce electricity. Many fish are able to create an electrical charge to use as “radar”. But this is one of the few species that can create a charge that’s strong enough to disable its prey!

The Electric Eel is really quite an enigma. It has the characteristics of a number of different types of fish. It could be grouped with other Unusual Fish types. Just like the Lungfish in that group that also have elongated eel like bodies, the Electric Eel needs to breath air. Their oral cavity (mouth area) has a vascularized respiratory organ and they are obligate air breathers. They mostly stay on the bottom of the aquarium, but will rise to the surface about every 10 minutes to gulp air. They get about 80% of their oxygen this way.

Even though it is eel shaped, the Electric Eel is not a true eel but is more closely related to many of the Knifefish that are found in South America. It is actually belongs in the Gymnotiformes Order of electric knifefishes, also known as the Neotropical or South American knifefishes, which contains six families. The family Gymnotidae, called the Naked-back Knifefishes, contains the banded knifefishes in the genus Gymnotus with 37 species and the genus Electrophorus which contains just this one species, this Electric Eel.

Like the the other electric knifefish, the Electric Eel has an elongated eel-like body. Its body is rounded and has no dorsal fin, but it does have an extremely long anal fin starting near the pectoral fin. This fin can move in an undulating forward or backward motion. All the members of this family have electric organs present and are able to generate a very weak electric field around their body which helps them identify objects.

The Electric Eel takes electricity generation to a much higher level than its relatives. It has a very large organ, and the electric organ of Electrophorus electricus has thousands of elements capable of producing electricity. Over 80% of its body is covered with elements. When it is at rest, there is no discharge, but as soon as it starts to move it emits pulses at a rate of about 50 per second. This is a frequency of 50Hz, but it is capable of generating shocks reaching 1 ampere and 600 volts. These extreme shocks are strong enough to paralyze most fish, and even mammals the size of a horse.

The Electric Eel uses electrical pulses to help with spatial orientation and to navigate as well as for hunting and self defense. It is believed that males also use an electric ‘stereotyped’ communication to court females. Two Electric Eels in the same aquarium frequently fight. They will take a head to tail position and start tail slapping and biting each other, and discharging electricity.

Because of their ability to generate a strong electrical charge, this large animal is definitely a candidate for a single species aquarium. Electric Eels are very hardy but avoid specimens that are less than 1 foot in length. For some reason, the smaller ones tend to be weak.

For Information on keeping freshwater fish, see:
Freshwater Aquarium Guide: Aquarium Setup and Care

Scientific Classification

• Kingdom: Animalia
• Phylum: Chordata
• Class: Actinopterygii
• Order: Gymnotiformes (Knifefishes)
• Family: Gymnotidae
• Genus: Electrophorus
• Species: electricus

Electric Eel – Quick Aquarium Care

• Aquarist Experience Level:

  Expert

• Size of fish – inches:

  98.4 inches (250.01 cm)

• Minimum Tank Size:

  200 gal (757 L)

• Temperament:

  Semi-aggressive

• Aquarium Hardiness:

  Moderately Difficult

• Temperature:

  74.0 to 82.0° F (23.3 to 27.8&deg C)

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Habitat: Distribution / Background

The Electric Eel Electrophorus electricus was described by Linnaeus in 1766. It is a very common South American fish and is found throughout most of the Amazon and Orinoco basins. This species is listed on the IUCN Red List as least concern (LC) because it has a very wide distribution, can adapt to many different habitats, and there are no significant threats identified.

These fish prefer to inhabit muddy calm waters, streams, pools and swamps with low oxygen levels. They can live in such low oxygenated waters because they are obligated air-breathers and will surface every ten minutes or so for air. They are also a nocturnal species that favors heavily shaded areas. They have very poor eyesight but can find their way around the dark waters by omitting around a 10 volt charge to navigate. They also use this charge like a radar to find prey.

When young they feed on invertebrates but as adults they feed on fish, amphibians, birds and small mammals that venture into the water. These fish are apex predators, meaning they virtually have no predators of their own. They use bursts of electricity to stun and kill their prey, or to protect themselves from predators if need be. They are capable of producing a charge up to about 600 volts.The power behind such a shock would be enough to knock a full grown horse off its feet.

This fish has a very unique breeding behavior. During the dry season the male will make a nest from its saliva and the female will then lay her eggs in the nest. She will produce thousands of eggs. As the eggs begin to hatch, the first of the fry are known to eat many of the unhatched eggs.

• Scientific Name:

  Electrophorus electricus

• Social Grouping:

  Groups

• IUCN Red List:

  LC – Least Concern

Description

The body of the Electric Eel is a elongated and cylindrical.

Photo © Animal-World: Courtesy Ken Childs

These are large fish that get up to 8 feet long (250 cm) and can weigh as much as 45 pounds (20 kg) in the wild. In captivity they are usually smaller, reaching only about 4 – 5 feet (125 – 152 cm) in length. They generally have a life span of 15 years.

This fish has no dorsal fin, but it does have an extremely long anal fin starting near the pectoral fin. This fin can move in an undulating forward or backward motion. The small tail fin is merged with the anal fin to form a continuous line. The head is flattened head and it has a large square mouth at the end of its snout.It has scales, but they are very small ctenoid scales, meaning they have a toothed outer edge.

Photo © Animal-World: Courtesy Clarice Brough

The body is mostly a dark grayish green with an orange throat. They eyes are emerald green. Juveniles are olive brown with yellowish spots.

One rather unique feature of the Electric Eel is that they gain almost 80% of their oxygen by gulping air at the surface. They have a vascularized respiratory organ in the oral cavity (mouth area). They will usually dwell on the bottom of the aquarium, and go to the surface for air about every 10 minutes or so.

Perhaps the most interesting feature of these fish is that they are capable of generating an incredible amount of electricity. They have a very large organ with thousands of elements capable of producing electricity. Over 80% of its body is covered with elements. They use electricity to stun and kill their prey, to communicate with others of their kind, and it is also thought that they may use it for finding and choosing a mate.

• Size of fish – inches:

  98.4 inches (250.01 cm) – This fish grows to over eight feet in the wild but will not exceed five feet in the home aquarium. Can get to around 45 pounds.

• Lifespan:

  15 years

Fish Keeping Difficulty

The Electric Eel is a fairly easy fish to take care of if you can meet the space requirements, equipment, and costs of feeding it. They are normally quite hardy, enjoy eating, and will feed on most any meaty offerings once they know it is food. That being said, this fish can be extremely dangerous because it can produce shocks of over 600 volts. Because of this it is only suggested for experienced fish keepers. These fish are best housed at zoos and aquariums, or by the dedicated fish keeper with the proper knowledge and equipment to keep and care for this very large and potentially dangerous fish.

• Aquarium Hardiness:

  Moderately Difficult – Although a hardy fish by nature, this fish should only be kept by competent, dedicated, and well equipped aquarists.

• Aquarist Experience Level:

  Expert

Foods and Feeding

Electric Eels are predatory fish, carnivores that will eat almost any animal that’s small enough to fit into their mouth. In the wild this mainly includes fish, invertebrates and small mammals. Juveniles can be fed worms and insect larvae, but larger specimens will prefer fish. You will probably have to feed them live food at first but usually they can be trained to eat dead freshwater fish such as defrosted frozen smelt, liver, and similar foods.

These fish become very tamed and associate the fish keeper with food and will come to the surface to be feed. Do not try to hand feed these fish. Although it is unlikely that they will shock you, the possibility is still there.

• Diet Type:

  Carnivore

• Flake Food:

  No

• Tablet / Pellet:

  No

• Live foods (fishes, shrimps, worms):

  Most of Diet

• Meaty Food:

  All of Diet

• Feeding Frequency:

  Daily

Aquarium Care

These fish need good water quality and are sensitive to changes in water conditions. These are big messy eaters and will need water changes of about 30 – 50% weekly, depending on the bio load. It is advisable to test the water often to assure that you have stable conditions. Make sure to keep the water level a few inches below the aquarium top as these fish will come to the surface in order to breath. When doing tank maintenance like gravel vacuuming or algae removal, make sure to wear rubber bottomed shoes. Use a long wooden-handled net to move the fish if needed.

• Water Changes:

  Weekly – Water changes of about 30-50% weekly.

Aquarium Setup

The Electric Eel is a very large fish that will spend most of its time on the bottom of the aquarium. In the wild this species can grow as large as 8 feet long and can weigh as much as 45 pounds, although the size attained in an aquarium will be smaller.

They are not a particularly active fish so they will not need a tank as large as other species their size would require. If the tank is longer that the fish is and it has plenty of room to turn around, it should suffice. But remember that even in captivity this fish can grow to over 4 or 5 feet.

This fish should be put into a very large aquarium right away because even as a small juvenile its growth rate is fast and steady. A minimum sized tank of 200 gallons (757 l) or more will be needed to house a single adult fish. Be ready to upgrade to a tank of 540 gallons (2040 l) or more if the specimens grows. A tank of about 2,500 gallons (9,463 L) would be required to house more than one. Soft, slightly acidic water is optimal but not important. The water level should be around 6 inches from the top because these fish need to come to the surface for air. The top needs to be securely fastened.

This is a massive messy fish and needs a large filter that can handle the bio load produced. It is best to have external equipment as this fish can easily break or damaged anything placed inside the tank. An external canister filter is also easier for maintenance. The Electric Eels need a darker aquarium with hiding places. Tank lighting should be subdued and bog wood and some rocks can work well for decor.

• Minimum Tank Size:

  200 gal (757 L) – This fish needs to stretch out completely. A 200 gallon (757 l) tank is bare minimum, be ready to upgrade to a tank of 540 gallons (2040 l) or more if the specimens grows. 2,500 gallons (9,463 L) or more will be needed to house more than one.

• Suitable for Nano Tank:

  No

• Substrate Type:

  Sand

• Lighting Needs:

  Low – subdued lighting

• Temperature:

  74.0 to 82.0° F (23.3 to 27.8&deg C)

• Range ph:

  6.0-8.5 – The Electric Eel is not very fussy about ph or water hardness. Soft, slightly acidic water is optimal but not important.

• Hardness Range:

  1 – 12 dGH

• Brackish:

  No

• Water Movement:

  Moderate

• Water Region:

  Bottom – They will spend most of their time resting on the bottom of the aquarium, but will need to surface for air about every 10 minutes.

Social Behaviors

The Electric Eel is not aggressive but due to its method of catching its prey, it is suitable only for a single species aquarium. More than one specimen can be kept in a tank, but this is risky. Larger specimens tend to be more peaceful, but juveniles will snap at their own kind. Two Electric Eels in the same aquarium frequently fight. They will take a head to tail position and start tail slapping and biting each other, and discharging electricity.

• Venomous:

  No – Although not venomous, it emits electrical pulses when it moves that can generate shocks.

• Temperament:

  Semi-aggressive – Other fish in the tank will be most often be attacked because this fish has a voracious appetite.

• Compatible with:

  • Same species – conspecifics:

    Sometimes – More than one can be kept if the tank is large enough. Young Electric eel are quite pugnacious with each other, although some will outgrow this and can be successfully kept with other adults.

  • Peaceful fish ():

    Threat

  • Semi-Aggressive ():

    Threat

  • Aggressive ():

    Threat

  • Large Semi-Aggressive ():

    Threat

  • Large Aggressive, Predatory ():

    Threat

  • Slow Swimmers & Eaters ():

    Threat

  • Shrimps, Crabs, Snails:

    Threat – is aggressive

Sex: Sexual differences

Females are normally larger then males when mature.

Breeding / Reproduction

Has not been bred in captivity. This Eel has a very unique breeding behavior. During the dry season the male will make a nest from its saliva. The female will then lay about 1,200 to 3,000 eggs in the nest which are then fertilized by the male. The eggs are left unguarded so subject to predation. As the eggs hatch, the first of the fry are known to eat many of the unhatched eggs.

• Ease of Breeding:

  Unknown

Fish Diseases

The biggest issue with most Electric Eel is starvation and sickness caused by lack of nutrition. These fish are hardy and disease is not usually a problem in a well maintained aquarium. That being said there is no guarantee that you won’t have to deal with health problems or disease. As with most fish they are prone to skin flukes, parasitic infestations (protozoa, worms, etc.), ichthyobodo infection, parasitic infestations (protozoa, worms, etc.), bacterial infections (general), and bacterial disease. Like other electric knifefish types, they are sensitive to some fish medications such as copper and those containing formalin.

The best way to proactively prevent disease is to give your fish the proper environment and give them a well balanced diet. The closer to their natural habitat the less stress the fish will have, making them healthier and happy. A stressed fish is more likely to acquire disease. Make sure to quarantine live food before feeding.

Anything you add to your tank can bring disease to your tank. Not only other fish but plants, substrate, and decorations can harbor bacteria. Take great care and make sure to properly clean or quarantine anything that you add to an established tank so not to upset the balance. Make sure to quarantine live food before feeding.

It is recommended to read up on the common tank diseases. Knowing the signs and catching and treating them early makes a huge difference. For information about freshwater fish diseases and illnesses, see Aquarium Fish Diseases and Treatments.

Availability

Electric Eels are commonly available but due to their specialized behavior, many aquarium fish suppliers do not carry them. You may need to place a special order to get one.

References

Author: Clarice Brough CFS, Ken Childs, Jeremy Roche