Electric Eel

Quick summary

The Electric Eel is an expert-only species that can deliver dangerous shocks of up to 480 volts, requires a minimum 3,000 litre species-only tank, and is not suitable for beginners or typical home aquariums. If you’re new to fishkeeping or lack institutional-grade facilities, this is not the fish for you.

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In this guide:

• Introduction
• Quick Stats
• Appearance
• Natural Habitat
• Tank Size and Setup
• Water Parameters
• Filtration and Equipment
• Diet and Feeding
• Behaviour and Temperament
• Tank Mates
• Breeding
• Common Diseases
• FAQs

Introduction

The Electric Eel (Electrophorus electricus) is arguably the most famous freshwater fish on Earth, and for good reason. Capable of producing electrical discharges of up to 480 volts, it is a genuine biological marvel. A 2019 taxonomic study split the traditional “Electric Eel” into three distinct species – this fish, Electrophorus electricus, along with E. varii and E. voltai – and found that a close relative, E. voltai, is actually the more powerful of the three, capable of discharges up to around 860 volts that has fascinated scientists, aquarists, and the general public for centuries. Found in the murky waterways of the Amazon and Orinoco basins in South America, this extraordinary species uses its electrical organ to stun prey, navigate its environment through electrolocation, and deter predators.

Despite its common name, the Electric Eel is not a true eel at all. True eels belong to the order Anguilliformes, an entirely separate group of fishes. The Electric Eel is actually a knifefish, classified within the order Gymnotiformes, making it most closely related to species such as the Banded Knifefish, Glass Knifefish, and Brown Ghost Knifefish. Its elongated, serpentine body shape is what historically earned it the misleading “eel” name, but anatomically and genetically it sits firmly among the South American knifefishes.

This is an expert-only species and must be treated as such. The Electric Eel is genuinely dangerous to handle. A discharge of 600 volts is more than enough to cause severe pain, muscle contractions, respiratory distress, and in rare circumstances – particularly if a person falls into water after being shocked – it can contribute to drowning. Even experienced aquarists must exercise extreme caution when performing tank maintenance, netting, or any procedure that involves proximity to the animal. This fish should never be kept by hobbyists who lack the experience, facilities, and understanding required to manage a large, potentially hazardous predatory species.

Beyond the safety concerns, the Electric Eel grows to a truly enormous size, routinely exceeding two metres in length in captivity. It requires a dedicated, purpose-built enclosure of exceptional volume – far beyond what the vast majority of home aquarists can provide. It is an obligate air-breather, surfacing regularly to gulp atmospheric air through a specialised, highly vascularised mouth lining, and will drown if denied access to the surface. It is also a solitary predator that cannot be housed with other fish, as it will shock and consume virtually any tank mate.

For all these reasons, the Electric Eel is most commonly seen in public aquaria and zoological institutions, where it continues to captivate visitors. Private keeping is rare and should only be undertaken by specialists with institutional-grade facilities. This guide provides comprehensive information for those with the resources, expertise, and commitment to care for one of the natural world’s most remarkable animals.

Appearance

The Electric Eel possesses one of the most distinctive body plans of any freshwater fish. Its form is powerfully elongated and cylindrical, tapering gently towards the tail end, giving it the superficial appearance of a large snake or eel. The body is essentially scaleless, covered instead in a thick, mucus-coated skin that offers some protection against parasites and its own electrical discharges. The overall silhouette is remarkably uniform – the head blends seamlessly into the trunk, and the trunk extends into a long, ribbon-like anal fin that runs along the entire underside of the body. This anal fin is the primary means of locomotion, undulating in graceful waves that propel the fish forwards and backwards with surprising agility for an animal of its size.

The head is broad and flattened, with a wide, upturned mouth adapted for both gulping air at the surface and engulfing prey. The eyes are small and relatively poorly developed, reflecting the species’ reliance on electrolocation rather than vision in its naturally turbid habitat. The gill openings are small and largely vestigial in terms of gas exchange – the vast majority of the animal’s oxygen intake occurs through the vascularised oral mucosa when it surfaces to breathe.

Colouration in adult specimens is typically dark olive-green to near-black across the dorsal surface and flanks, transitioning to a somewhat lighter shade on the ventral surface. Juvenile specimens often display a more pronounced pattern, with irregular yellowish-orange or cream-coloured mottling on a dark background, particularly on the chin and throat. This mottling tends to fade with age, though some adults retain a degree of lighter colouration on the underside of the head. The skin has a slightly oily, glossy appearance when the animal is healthy, owing to the copious mucus layer.

Approximately 80% of the Electric Eel’s body volume is devoted to the three specialised electric organs – the main organ, Hunter’s organ, and Sachs’ organ – which are composed of thousands of modified muscle cells called electrocytes, stacked in series like batteries. The vital organs, including the heart, digestive system, and reproductive organs, are all compressed into the anterior fifth of the body. This extraordinary anatomical arrangement is visible externally as a subtle thickening behind the head that gives way to the more uniform, muscular posterior portion.

Adults routinely reach 180 to 220 cm in length and can weigh in excess of 20 kg. The largest verified specimens have exceeded 250 cm. There is some sexual dimorphism, with males generally growing larger than females, though this is difficult to determine visually without comparing known specimens side by side. Growth rate is rapid in the first few years of life, and even in captivity, juveniles of 30 cm can reach over a metre within two to three years given adequate nutrition and tank space.

Natural Habitat

The Electric Eel inhabits a range of freshwater environments across the Amazon and Orinoco river basins, spanning portions of Brazil, Venezuela, Colombia, Ecuador, Peru, and the Guianas. It shows a strong preference for calm, slow-moving, or stagnant waters, including swamps, floodplain pools, creeks, and the still backwaters of larger rivers. It is particularly associated with heavily vegetated, oxygen-depleted environments where its ability to breathe atmospheric air gives it a significant survival advantage over purely gill-breathing fish.

The waters in its native range are typically warm, soft, and slightly acidic to neutral, though the species demonstrates considerable tolerance for variation. Many of its preferred habitats are characterised by dark, tannic-stained water with extremely poor visibility, heavily shaded by overhanging vegetation and submerged plant matter. The substrate tends to be soft mud or decomposing leaf litter, and the water is often virtually devoid of dissolved oxygen due to the high organic load. These are challenging environments for most aquatic life, but the Electric Eel thrives thanks to its dual adaptations of air-breathing and electrolocation.

Electric Eels are primarily nocturnal in the wild, spending daylight hours resting in sheltered positions among dense vegetation, submerged roots, or muddy depressions. At night, they become active hunters, using low-voltage electrical pulses for navigation and prey detection, and high-voltage discharges to stun fish, crustaceans, and other prey items. They are apex predators in their micro-habitats and have few natural enemies as adults, though juveniles may fall prey to caimans, large catfish, and wading birds.

Recent taxonomic work has suggested that what was historically considered a single species, Electrophorus electricus, may actually comprise three distinct species: E. electricus, E. voltai, and E. varii, each occupying somewhat different geographical ranges and habitats within the broader Amazon-Orinoco system. E. voltai, found primarily in the Brazilian Shield region, has been recorded producing discharges of up to 860 volts, making it the strongest bioelectricity generator known. For practical purposes in the aquarium hobby, these species are treated interchangeably, as their care requirements are essentially identical and trade identification to species level is unreliable.

Tank Size and Setup

The minimum tank size for an adult Electric Eel is 3,000 litres, and considerably larger enclosures are strongly recommended. This is not a fish that can be “grown into” a larger tank – growth is rapid, and a juvenile purchased at 20 or 30 cm will need access to a suitably enormous enclosure within a few years at most. Ideally, the tank should be at least 300 cm long, 90 cm wide, and 60-75 cm deep. The relatively modest depth is intentional: the Electric Eel must surface to breathe, and excessively deep tanks make this more difficult and stressful. A gap of at least 10-15 cm between the water surface and the tank lid must be maintained to allow the fish to gulp air comfortably.

The tank must be securely covered at all times. Electric Eels are powerful and can push aside loose-fitting lids. A tight, weighted cover is essential to prevent escapes, which can be fatal for the fish and dangerous for anyone who encounters a large Electric Eel out of water. The cover must also prevent the keeper’s hands from inadvertently entering the water during routine checks – a dedicated feeding hatch or port is advisable.

Decor should be kept to a minimum. Large, smooth structures such as PVC pipes of appropriate diameter, smooth rocks, or large pieces of driftwood can provide the fish with a sense of security and a place to rest, but the majority of the tank floor should be open to accommodate the animal’s considerable size. Sharp edges, rough rocks, and abrasive substrates should be avoided, as the scaleless skin of the Electric Eel is vulnerable to abrasion injuries that can quickly become infected. A soft sand substrate or bare-bottomed tank is most practical, with a bare bottom being easiest to maintain hygienically.

Live plants are neither necessary nor practical in an Electric Eel enclosure. The fish’s size and activity level will uproot or crush most plantings, and the electrical discharges may stress sensitive aquatic plants. Floating plants can be used if desired to reduce light levels and provide a more naturalistic feel, but they will need frequent replacement.

All electrical equipment in and around the tank must be rated for use with electric fish, and ground fault circuit interrupter (GFCI/RCD) protection is absolutely essential. The fish’s electrical discharges can interfere with electronic equipment, trip circuits, and pose a genuine electrocution risk to the keeper if proper precautions are not taken. Submersible heaters and other in-tank electronics should be housed in protective guards or, where possible, replaced with external alternatives (such as inline heaters) that do not share the water column with the animal. All wiring and plugs should be kept well clear of any potential water splashes.

Water Parameters

The Electric Eel is reasonably tolerant of a range of water chemistries, which is one of the few aspects of its care that could be described as forgiving. In the wild, it inhabits waters that are typically soft and slightly acidic, but captive specimens adapt well to moderately hard, neutral to slightly alkaline conditions commonly found in municipal tap water. Stability is more important than hitting a precise target – avoid sudden swings in pH or temperature.

Temperature should be maintained between 25 and 28 °C. The Electric Eel is a tropical species and does not tolerate sustained exposure to temperatures below 22 °C. Heating a tank of 3,000 litres or more requires powerful, reliable equipment, and redundancy is advisable – a heater failure in a large volume of water can cause a dangerously rapid temperature drop, particularly in cooler climates.

Water quality management is a significant challenge given the volume of waste produced by a large carnivorous fish in a very large tank. Ammonia and nitrite must be maintained at zero at all times. Nitrate should be kept below 40 ppm, with lower levels always preferable. Large, regular water changes – typically 30-50% weekly – are the cornerstone of water quality maintenance. The logistics of draining and refilling thousands of litres of water weekly should be carefully considered before acquiring this species; a permanent plumbed water change system with dechlorination is highly recommended for enclosures of this scale.

Filtration and Equipment

Filtration for an Electric Eel enclosure must be robust, oversized, and preferably external to the tank. Large canister filters, sump systems, or custom-built filtration setups rated for well above the actual tank volume are the standard approach. A sump-based system is generally the most practical option for tanks of 3,000 litres and above, as it provides substantial biological filtration capacity, allows equipment to be housed outside the main tank (away from the animal and its electrical discharges), and facilitates easier maintenance.

Biological filtration should be the primary focus, as the Electric Eel produces a considerable bioload. High-quality biomedia with a large surface area should be used in generous quantities. Mechanical filtration to remove particulate waste is also important, as the fish produces copious mucus and food debris. Chemical filtration, such as activated carbon, can be employed if desired but is not strictly necessary if water changes are performed regularly and consistently.

Water movement should be gentle to moderate. The Electric Eel is not a fish of fast-flowing waters and will be stressed by strong currents. Filter outlets should be positioned to provide adequate circulation without creating powerful flow patterns. Spraybars or diffusers can help distribute water movement more evenly across the tank.

All submersible equipment must be protected from the fish’s electrical discharges and physical bulk. Heater guards, filter intake guards, and secure mounting are essential. Where possible, use inline heaters and external equipment to minimise the number of devices in the water column. Lighting should be subdued – the Electric Eel is a largely nocturnal species with poor eyesight and does not require or appreciate bright illumination. A simple LED strip on a timer, providing a gentle day/night cycle, is sufficient.

An air gap above the water surface is critical. The tank lid should be secure but must allow for an accessible airspace. The Electric Eel surfaces to breathe every few minutes, and restricting access to air will lead to drowning. Ensure that condensation and dripping from the lid do not create a seal over the water surface.

Diet and Feeding

The Electric Eel is a carnivorous predator that feeds primarily on fish, crustaceans, and invertebrates in the wild. In captivity, it should be offered a varied diet of whole prey items to ensure adequate nutrition. Appropriate foods include whole fish (such as lance fish, smelt, or tilapia fillets), large earthworms, prawns, mussels, and other seafood. Some keepers also offer commercially available carnivore pellets or gel foods as supplementary items, though these are unlikely to form the bulk of the diet for most specimens.

Live feeder fish should be avoided. They carry a significant risk of introducing parasites and diseases, and the ethical and welfare concerns around live feeding are substantial. The Electric Eel will readily accept dead or thawed prey items once accustomed to them, and most captive specimens transition to non-live food without difficulty. Tong-feeding is the standard approach, but the keeper must exercise extreme caution – long, insulated feeding tongs (at least 60 cm) should be used, and hands should never enter the water.

Juvenile Electric Eels should be fed daily or every other day, with portions appropriate to their size – a rough guideline is prey items equivalent to around 5% of the fish’s body weight per feeding. As the animal matures and growth slows, feeding frequency can be reduced to two to three times per week. Adult specimens over 150 cm often do well on a twice-weekly feeding schedule. Overfeeding should be avoided, as it contributes to water quality deterioration and obesity, both of which can lead to health problems.

Vitamin and mineral supplementation can be provided by occasionally soaking prey items in a liquid vitamin preparation before offering them, or by feeding whole prey fish that have themselves been gut-loaded with nutritious foods. Variety is key to long-term health – a diet consisting solely of one type of prey item can lead to nutritional deficiencies over time.

Behaviour and Temperament

The Electric Eel is a solitary, largely sedentary species that spends much of its time resting motionless on the substrate or among decor, punctuated by regular trips to the surface to breathe. Activity levels tend to increase during the evening and night, reflecting its nocturnal habits in the wild. Despite its somewhat sluggish appearance, the Electric Eel is capable of rapid bursts of movement when hunting or startled, and it can navigate its environment with remarkable precision using its electrosensory system.

The species is not aggressive in the conventional sense – it does not chase or harass other animals for territorial reasons. However, it is an apex predator that will shock and consume any fish or invertebrate small enough to be considered prey, and its electrical discharges can injure or kill animals far too large to eat. It must be housed alone. There is no safe tank mate for an Electric Eel in a typical aquarium context.

Electric Eels in captivity can become surprisingly responsive to their keepers over time. Many long-term captive specimens learn to associate the approach of their keeper with feeding and will surface or move to a particular part of the tank in anticipation. Some individuals tolerate close proximity to the glass without discharging, while others are more reactive. Each animal has its own temperament, and keepers should learn the behaviour patterns of their individual specimen to minimise stress and risk.

Low-voltage electrical pulses are emitted continuously for navigation and environmental sensing. These are not harmful and are a normal part of the animal’s behaviour. High-voltage discharges are produced when the fish is hunting, startled, or feels threatened. Keepers should be aware that a stressed or startled Electric Eel may discharge without warning, and this discharge can travel through the water and any conductive material in contact with it. Rubber gloves and insulated tools should be used for all maintenance, and the keeper should avoid simultaneous contact with the water and any grounded object.

Tank Mates

The Electric Eel should be kept strictly alone. This is not a community fish by any stretch of the imagination, and no other species can be safely or responsibly housed with it. Its high-voltage discharges will stun, injure, or kill other fish, and any animal small enough to be consumed will be treated as food. Even large, robust species are at serious risk of injury from electrical shocks. Attempting to keep tank mates with an Electric Eel is irresponsible and will almost certainly result in the death or injury of the companion animals.

Good tank mates

• None – the Electric Eel must be housed alone in a species-only enclosure due to its high-voltage electrical discharges and predatory nature.

Fish to avoid

• Oscar – will be shocked and likely killed or consumed, despite its size.
• Common Pleco – vulnerable to electrical discharges and will be stressed or killed in the same enclosure.
• Red-bellied Piranha – despite their reputation, piranhas are easily stunned and killed by Electric Eel discharges.
• Silver Arowana – a large species that nonetheless cannot withstand high-voltage shocks and will be severely injured.
• Redtail Catfish – another large predator, but still at serious risk of injury from electrical discharges.
• Banded Knifefish – a fellow knifefish that would be particularly sensitive to electrical interference and easily preyed upon.

Breeding

Breeding the Electric Eel in captivity is exceptionally rare and has only been achieved under highly specialised institutional conditions. The overwhelming majority of hobbyists will never attempt or witness captive reproduction of this species, and it is generally considered beyond the scope of private aquarium keeping.

In the wild, breeding behaviour is associated with the onset of the rainy season, when water levels rise and new flooded habitats become available. Males are reported to construct nests from saliva-bound vegetation or foam in shallow, sheltered areas. The female deposits eggs into the nest, which are then guarded by the male. Clutch sizes can be large, with reports of several thousand eggs per spawning event. The male continues to guard the nest and the hatched fry, using low-voltage discharges to deter potential predators. Fry are initially very small and feed on tiny invertebrates and insect larvae.

Attempting to breed Electric Eels in captivity would require at minimum two enormous enclosures (one for each adult, as they cannot be safely cohoused long-term), a means of introducing the pair for spawning under carefully controlled conditions, and the ability to simulate seasonal environmental changes including significant water level fluctuations, temperature shifts, and changes in photoperiod. The risks involved – both to the animals and to the keeper – are substantial, and breeding attempts should only be undertaken by experienced professionals in an institutional setting with appropriate veterinary and safety support.

Sexing Electric Eels visually is extremely difficult. Males tend to be larger and may develop a slightly broader head as they mature, but these differences are subtle and unreliable without comparison specimens. Hormonal assays or ultrasound examination by a qualified aquatic veterinarian are more reliable methods for sex determination.

Common Diseases

The Electric Eel is a reasonably hardy species when maintained in appropriate conditions, but its scaleless skin and large size make it vulnerable to certain health issues, particularly those related to water quality and physical injury.

Bacterial skin infections are perhaps the most common health problem encountered in captive Electric Eels. The scaleless skin is susceptible to abrasion from rough surfaces, sharp decor, or aggressive netting, and any wound can quickly become infected in suboptimal water conditions. Symptoms include reddened patches, ulceration, white or grey fuzzy growths, and loss of the protective mucus layer. Treatment typically involves improving water quality, removing the source of injury, and in severe cases, antibiotic treatment prescribed by an aquatic veterinarian. Medicating an Electric Eel tank is complicated by the animal’s electrical capabilities – any treatment procedure that requires close physical contact with the fish carries genuine risk to the keeper.

Fungal infections (saprolegniasis) can affect wounds or areas of damaged skin, presenting as cotton-like white growths. These are usually secondary to bacterial infections or physical damage and respond to antifungal treatments combined with water quality improvements.

Internal parasites can be present in wild-caught specimens, which most Electric Eels in the trade are. Symptoms may include weight loss despite adequate feeding, lethargy, and abnormal faeces. Diagnosis and treatment should be carried out under veterinary guidance, as the dosing of antiparasitic medications for a fish of this size requires careful calculation.

Nutritional deficiencies can develop if the diet is monotonous or overly reliant on a single prey type. Thiamine (vitamin B1) deficiency is a particular risk if the fish is fed exclusively on certain types of frozen fish (especially smelt or other thiaminase-containing species) without supplementation. Symptoms include loss of appetite, erratic swimming, and in severe cases, neurological impairment. Varied feeding and occasional vitamin supplementation are the best preventive measures.

Stress-related illness is a broader concern. Electric Eels that are kept in tanks that are too small, too brightly lit, or too heavily trafficked may exhibit chronic stress, leading to suppressed immune function and increased susceptibility to opportunistic infections. Providing a suitably large, dimly lit, quiet enclosure with minimal disturbance is the single most important factor in preventing disease.

FAQs

Can an Electric Eel kill a human?

While fatalities directly attributed to Electric Eel shocks are extremely rare, the discharge of up to 600 volts (and potentially over 800 volts in some recently described species) is powerful enough to cause severe pain, involuntary muscle contractions, temporary paralysis, and cardiac disruption. The primary danger in an aquarium context is that a shock could incapacitate a person whose hands or arms are in the water, leading to a fall or drowning. Electric Eels must always be treated with the utmost respect, and appropriate safety precautions – including insulated tools, GFCI/RCD-protected circuits, and never working alone around the tank – must be observed without exception.

Is the Electric Eel really an eel?

No. Despite its common name and elongated body shape, the Electric Eel is not a true eel. True eels belong to the order Anguilliformes, while the Electric Eel is a member of the order Gymnotiformes – the South American knifefishes. Its closest relatives include the Banded Knifefish, Glass Knifefish, and Brown Ghost Knifefish, all of which share the characteristic undulating anal fin and electrosensory capabilities, though none approach the Electric Eel’s voltage output.

How big a tank does an Electric Eel need?

An adult Electric Eel requires a minimum tank volume of 3,000 litres, with dimensions of at least 300 cm long and 90 cm wide. Larger is always better. The tank should not be excessively deep, as the fish must surface regularly to breathe atmospheric air. A depth of 60-75 cm with an airspace of 10-15 cm above the waterline is generally appropriate. Most private homes cannot accommodate a tank of this size, which is one of the many reasons this species is best suited to public aquaria and specialist facilities.

What does an Electric Eel eat?

In captivity, Electric Eels should be fed a varied diet of whole fish (such as lance fish, smelt, and tilapia), prawns, mussels, and large earthworms. Live feeder fish should be avoided due to the risk of disease transmission. Adults can be fed two to three times per week, while juveniles require more frequent meals. All feeding should be done using long, insulated tongs – never place your hands in the water.

Can I keep an Electric Eel with other fish?

Absolutely not. The Electric Eel must be kept strictly alone. Its high-voltage discharges will stun, injure, or kill any other fish in the same enclosure, regardless of species or size. Even large, robust species such as Arowanas or large catfish cannot safely coexist with an Electric Eel. There are no compatible tank mates for this species.

Related Guides

• Banded Knifefish – A fellow Gymnotiform knifefish and one of the Electric Eel’s closest relatives, offering an interesting comparison in care requirements and biology.
• Glass Knifefish – Another South American knifefish in the order Gymnotiformes, sharing the electrosensory capabilities but far more manageable in a home aquarium setting.
• Brown Ghost Knifefish – A related Gymnotiform species that demonstrates similar body form and electrolocation abilities at a much more practical size for private keeping.
• Black Ghost Knifefish – One of the most popular knifefish in the aquarium trade, providing a hobbyist-accessible introduction to the fascinating world of electric fish.
• Silver Arowana – Another large South American predatory fish requiring a substantial tank, offering useful parallels in terms of large-fish husbandry challenges.