Electric Eel

The South American electric fish name is the electric eel. It was classified as the only species that is present in its genus and it was identified recently. Except for the name, this fish is not an eel, but rather it is known as knife fish. It is considered a freshwater fish of a larger group that contains an electrogenic tissue that produces electric discharges. The electric eel has a slender, snake-like body and a flattened head. Its skin is thick and scaleless, it is generally dark gray to brown in color, and its underside is a yellow-orange color. Similar to other types of eel-shaped fish, the electric eel lacks pelvic fins. It has a small, or reduced, caudal fin and also lacks the dorsal fins as well. Instead of these fins, an elongated anal fin helps the fish to maneuver through the water easily. By this, it can swim forward, or backward or hover, as it searches for its prey.

There are three specialized electric organs that are found in the electric fish: the main electrical organ, Hunter’s organ, and the Sachs’ organ. These organs make up about 80 percent of the fish’s body. Its remaining vital organs are tightly packed within the anterior, or front, part of its body. The electric organs are capable of creating both strong and weak electric charges. These electric charges are utilized for different purposes such as hunting, defense, communication, and navigation. Stronger electric charges can be energetically exhausting for this fish. Its strongest electric pulses are produced by the main electrical organ where Hunter’s organ contributes about two-thirds of the overall pulses. The remainder of Hunter’s organ and the Sachs’ organ produces the weaker electric discharges.

Electrophorus Fish Genus Classification

Kingdom: Animalia: It is classified under kingdom Animalia. The kingdom Animalia is also known as Metazoa and it includes all animals. These animals are multicellular in nature, these are also known as eukaryotic organisms. These are said to be heterotrophic, which means that they obtain the required nutrition from organic sources. Most of the animals obtain the required nutrition by ingesting other organisms or through the process of decomposition by decomposing the organic material.

Phylum: Chordata: Under the kingdom Animalia it belongs to the phylum Chordata. An animal of the phylum Chordata is known as chordate. All the chordates in this phylum possess five synapomorphies or the primary characteristics. During their adulthood or larval stages, they can distinguish at some point from all the other taxa. These five synapomorphies or the primary characteristics include a dorsal hollow nerve cord, notochord, endostyle or thyroid, pharyngeal slits, and a post-anal tail. The chordates get their name from one of their primary characteristic “notochord”. This notochord plays a significant role in the structure and movement of a chordate. Chordates are also bilaterally symmetric, these have a coelom, consist of a circulatory system, and capable of exhibiting metameric segmentation.

Class: Actinopterygii: Electric shock fish is classified under class Actinopterygii. The members of this class are known as ray-finned fishes, these belong to a clade of the bony fishes. The ray-finned fishes are called so because their fins are in the form of webs of the skin that are supported by bony or horny spines.

Order: Gymnotiformes: The next level of classification is the order these electric eel fishes belong to the order Gymnotiformes. The organisms in this order are a group of the teleost bony fishes that are commonly known as the Neotropical or South American knife fish. These fishes have long bodies and they use undulations of their elongated anal fin for the purpose of swimming.

Family: Gymnotidae: After the order next comes the family they belong to the family Gymnotidae Rafinesque. It is represented by a total of 46 valid species and seven valid subspecies along with this, these have at least two additional species that are currently known and are described elsewhere. Despite its relative species richness, the family Gymnotidae is currently divided into only two supraspecific taxa. One of the taxa is the subfamily Electrophorinae with a single genus and three valid species. The other subfamily is Gymnotinae also with a single genus and 43 valid species.

Genus: Electrophorus: The next level of classification is the genus, the electric fish belongs to the genus Electrophorus. It is a genus of the Neotropical freshwater fish that belongs to the family Gymnotidae. Over two centuries it was believed to be a monotypic genus until the unexpected discovery of two additional species in 2019. It includes the strongest bio-electricity generator that is found in nature, Electrophorus volta.

Species: E. Electricus: The last level of classification is species, the electric eel fish genus belongs to the species of electricus.

Electric Fish - Anatomy

The electric eel fish has an elongated body that is cylindrical in shape. Typically these fishes grow to about two meters in length and have about 20 kg or 44 lb in weight. These are the largest species of the order Gymnotiformes. Their skin coloration is dark gray-brown on the backside and yellow or orange on the belly. The mature females have a darker color on the side of the abdomen. These are lacking in the scales. The mouth is square in shape and it is positioned at the end of the snout. The anal fin helps to extend the length of the body to the tip of the tail.

As in other ostariophysan fishes, the swim bladder consists of two chambers. One of the chambers is the anterior chamber; it 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 respiratory system is vascularized where the gaseous exchange occurs through the epithelial tissue that is present in the buccal cavity. As obligate air-breathers, for every ten minutes, these electric eels must rise to the surface or so to inhale before returning to the bottom. Nearly eighty percent of the oxygen used by the fish is obtained in this way.

The electric eel is not closely related to the true eels which are Anguilliformes. But these are considered as a member of the neotropical knifefish order that is Gymnotiformes, this order is more closely related to the catfish.

[Image will be Uploaded Soon]

Electric Eel Fish - Physiology

The electric eel has three pairs of abdominal organs that are involved in the production of electricity. These organs are as follows: main organ, Hunter's organ, and Sachs' organ. These organs make about four-fifths of its overall body and give the electric eel the ability to generate two types of electric organ discharges. The two types of electrical discharges involve low voltage and high voltage. These organs are made of specialized cells called electrocytes. These are lined up as a current of ions that can flow through them and are stacked so each one of the ions adds to a potential difference. The three electrical organs are developed from muscle and they are capable of exhibiting several biochemical properties and morphological features of the muscle sarcolemma. Symmetrically along both sides of the eel, these are found.

When the eel finds its prey, through the nervous system the brain sends a signal to the electrocyte. This opens the ion channels that allow the sodium to flow through, reversing this polarity momentarily. By causing a sudden difference in electric potential, it generates an electric current. The generated electric current is in a manner that is similar to a battery, in which the plates are stacked where each of them produces an electric potential difference. Electric eels are also capable of controlling their prey's nervous systems with their electrical abilities. This can be done by controlling their victim's nervous system and muscles with the help of electrical pulses. These can keep their prey from escaping or force it to move so that they can locate its position.

In the electric eel, about 5,000 to 6,000 stacked electroplates are capable of generating a shock of up to 860 volts and a current of up to one ampere. Electric eels make use of electricity in multiple ways. The produced low voltages are used to sense the environment that is surrounding them. High voltages produced are used in the detection of prey. Pairs of high voltage pulses are separated by two milliseconds. These pulses are used to detect and locate the prey by causing them to twitch or provide sudden jerk involuntarily. The electric eel can sense this movement easily. A string of high voltage pulses is 400 per second is then used to attack and paralyze the respective target. It is the point at which the electric eel applies a suction-feeding bite.

Sachs' organ is associated with electrolocation. Inside this organ, there are many muscle-like cells, known as electrolytes. Each cell can only produce up to 0.15 V, even though this organ is capable of transmitting a signal of nearly 10 V in amplitude and around 25 Hz of frequency. These signals are emitted by the main organ. The Hunter's organ is capable of emitting the signals at the rate of several hundred hertz.

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 section of the voltage of Hunter's organ are rich in a mineral called calmodulin. It is a protein that is involved in the production of high-voltage. The high expression of this protein has an effect on the main and Hunter’s organs. This effect gives it a high sensitivity to changes in the ion concentration, whereas the Sachs' organ has a low expression of this protein.

The electric eel is unique among the animals under order Gymnotiformes. By having large electric organs that are capable of producing potentially lethal discharges that allow them to stun the prey. The larger voltages have been reported whereas only the typical output is sufficient to stun or deter the prey virtually to any animal. Juveniles are capable of producing smaller voltages. They can vary the intensity of the electric discharge, using lower discharges for hunting. The higher intensities are used for stunning the prey or for defending themselves. They can also concentrate on the discharge by curling up and making contact at two points along its body. 

The electric eel also possesses receptors that are highly sensitive to frequency tuberousness. These are distributed in the patches over its body. This feature is apparently useful for hunting other animals of the order Gymnotiformes. In the study of bioelectrogenesis, Electric eels have been used as a model. The species is of some interest to researchers, those who make use of its acetyl-cholinesterase and ATP (adenosine triphosphate).

The electrical properties of an electric eel fish were tested by Michael Faraday extensively. For a span of four months, Faraday carefully measured the electrical impulses that are produced by the animal. It was measured by pressing the shaped copper paddles and saddles against the used specimen. Through this method, Faraday quantified and determined the direction and magnitude of the electric current. He also proved that the animal's impulses were in fact electrical, this was said by observing the sparks and deflections found on a galvanometer.

Electric Eel Fish - Behaviour

Electric Discharge: These famous freshwater predators get their name due to the production of enormous electrical charge that is used to stun the prey and dissuade the predators. Their bodies contain electric organs with about 6,000 specialized cells, these cells are called electrocytes that store power like tiny batteries. When threatened or while attacking the prey, these cells will discharge simultaneously.

Diet: They live in the murky streams and ponds on the Amazon and basins of Orinoco of South America. These feed mainly on the fish present in the water bodies, but also with amphibians and even birds and small mammals. As air-breathers, they have to come to the surface frequently in order to take the oxygen. They also have poor eyesight but they can emit a low-level charge, that is less than ten volts, it is the charge in which they use as a radar to navigate and locate the prey.

Threats to Humans: Human deaths from electric eels are extremely rare. However, multiple electric eel shocks can cause respiratory or heart failure. The people have been known to drown in shallow water after a stunning jolt.

Reproduction: Electric eels can reproduce only during the dry season. The eggs of these fishes are deposited in a hidden well nest that is made of saliva. These hidden wells are usually built by the males. In the field observations, an average of 1200 embryos were hatched. Their ability to produce the count of offspring has been documented as high as 17,000 eggs. The electric eel is thought to be a fractional spawner.

Lifespan or Longevity: The lifespan of electric eels is unknown in the wild. In captivity, male fishes can live between 10 and 15 years, while female fishes usually survive between 12 and 22 years.

Communication and Perception: The Sachs organ is the primary source of communication among E. electricus. This organ transmits a weak signal that is about 10V in amplitude. These signals are used in communication as well as orientation. But these are not useful only to find the prey but also thought to play an important role in finding and choosing a mate. Scientists have been able to determine through experiments that the E. electricus has a well-developed sense of sounds. They have a Weberian apparatus that connects the ear and the swim bladder which greatly enhances their hearing capability.

Predation: The predation of the electric eels is usually prevented by their capability of electric shock. They can produce a voltage as high as that of 650 volts. Although this shock is deadly in rare cases it is enough to deter most of its predators. These defensive electrical pulses are created by two organs that are present in the E. electricus, these are the Main and Hunter organs. It is the strength of these two organs and the electric eels pulsating electric current that classifies it as a strongly electric fish.

Electric Eel Sting: The average shock that is caused due to electric eel can last for about two-thousandth of a second. The pain will not be to that extent, it can cause muscle contraction, and then causes numbness.

[Image will be Uploaded Soon]

Electric Fish - Facts

1. Electric eels are not actually considered eels. These are the members of the family of knife fish.

2. These animals belong to the native to the South American rivers, but they don’t spend all their time underwater. They have to come to the surface in order to breathe since these are air-breathers.

3. All of an electric eel vital organs are completely filled into the front for about 20 percent of its body. The rest is packed with 6000 cells that act like tiny batteries.

4. With that much body devoted to the production of electricity, it’s no wonder an eel can zap out the voltage of more than about 600 volts!

5. An eel’s voltage is great for defense purposes, but it also comes in handy while stunning prey, mostly for the crustaceans, and the small fishes.

6. Electric eels can’t see what they’re shocking since they are mostly blind and use a radar-like system of electrical pulses to navigate and to locate the food.

7. The thick skin of the eel is normally insulated to prevent their own attacks, but when wounded, they’ll shock themselves!

8. A fully grown electric eel can be up to eight feet long and weigh up to 44 pounds!

9. The fatal attacks on humans are rare, but that doesn’t mean eels are harmless. People have drowned after being shocked.