Electric eel

Electric eels are special fish that live in freshwater in South America. They belong to a group called Electrophorus and are famous for being able to create electricity to stun their prey. They can produce shocks of up to 860 volts, which is strong enough to surprise anyone who touches them!

These fish were first studied in 1775, and their abilities helped scientists create the first electric battery in 1800. Even though they are called "eels," they are not really related to true eels. Instead, they are part of a group of fish called knifefish, which are more closely related to catfish.

Electric eels hunt at night and breathe air directly from the surface. They have poor eyesight but can sense their surroundings using electricity. They mainly eat other fish and can keep growing bigger their whole lives by adding more bones to their spine. Males are usually larger than females, and some kept in aquariums have lived for more than 20 years.

Evolution

Taxonomy

When scientists first described electric eels in 1766, they placed them in the same group as another fish called the banded knifefish. Later, in 1864, they were moved to their own special group named Electrophorus, which means "electricity bearer." By 1998, electric eels were grouped with another family of fish called Gymnotidae.

In 2019, scientists looked closely at electric eels and found that there are actually three different species, not just one. These species have small differences in their bodies and how much electricity they can produce.

Phylogeny

Electric eels are part of a group of fish that can produce electricity, but they are not related to true eels. These fish evolved their ability to produce electricity a long time ago. Most of these fish can sense their surroundings with small electric signals, but only electric eels can give strong electric shocks.

Species

There are three known species of electric eels. They look quite similar but have some differences. One species can produce the strongest electric shock in nature, up to 860 volts. Another has a thicker skull, and the third has a more variable head shape.

Ecology

Electric eels live in different parts of northern South America. The species E. electricus lives in the northern area called the Guiana Shield, while E. voltai lives in the southern area, from the Brazilian shield northwards. Both of these species live in upland waters. The species E. varii lives in central areas, mostly in lowlands with many different habitats like streams, grasslands, and ponds. The water level in these areas changes a lot between the wet and dry seasons. All electric eels live on muddy river bottoms and sometimes in swamps, preferring shady areas. They can survive in water with low oxygen by coming to the surface to breathe air.

Electric eels are mostly active at night. E. voltai mainly eats fish, especially a type called the armoured catfish Megalechis thoracata. One E. voltai was found to have eaten a caecilian, a legless amphibian called Typhlonectes compressicauda, which might mean this eel can handle the caecilian’s toxic skin. E. voltai sometimes hunts together in groups and has been seen targeting a group of tetras, working together to catch them. The other species, E. varii, also eats fish, especially types known as Callichthyidae (armoured catfishes) and Cichlidae (cichlids).

Biology

Electric eels have long, sturdy bodies that are cylindrical at the front and flattened toward the tail. They can grow up to 2 meters (about 6 feet 7 inches) long and weigh as much as 20 kilograms (about 44 pounds). Their mouths are located at the front of their snouts and open upwards. They have smooth, thick skin that ranges from brown to black on top with a yellow or red belly, and they do not have scales.

Electric eels can produce strong electric shocks to find and stun their prey. They can generate up to 600 volts, which is powerful enough to surprise animals much larger than themselves. These shocks happen very quickly, lasting only a fraction of a second. Their bodies are specially designed to create and control these electric pulses, helping them navigate their environment and defend themselves.

Life cycle

Electric eels have a special way of having babies during the dry season, from September to December. During this time, male and female eels gather in small pools left behind when the water level drops. The male builds a nest using his saliva, and the female lays about 1,200 eggs for fertilisation. The baby eels, called spawn, hatch after seven days, and their mothers keep laying more eggs during the breeding season. When the baby eels grow to about 15 mm, they start eating any leftover eggs. Once they reach 9 cm, they begin eating other foods.

Male electric eels grow larger than females and become ready to reproduce at around 1.2 meters, while females start reproducing at about 70 cm. Both parents take care of the young for four months. As electric eels grow, they add more bones to their spine. They can produce electric shocks even when they are just 7 cm long. Some electric eels in captivity have lived for over 20 years.

Interactions with humans

Early research

The electric eel was first written about in 1583 by a priest named Fernão Cardim. In the 1760s, scientists began testing the electric shocks these fish could give. By 1775, important scientists like John Hunter studied the electric organs inside the eel. These organs are made of special cells that create electricity.

These early studies helped scientists understand electricity better and even led to the invention of the electric battery. In 1800, explorer Alexander von Humboldt watched people use horses to catch electric eels. The horses’ hooves would scare the eels out of the mud, and the eels would shock the horses with electricity. Later, scientist Michael Faraday tested the electricity of an electric eel and learned more about how it works.

Artificial electrocytes

Scientists have studied the special cells in electric eels to learn about electricity. In 2008, they made tiny artificial cells that act like the eel’s electric cells. These could help power small medical devices. By 2016, scientists created flexible materials that mimic the eel’s electricity, which might be used in watches or lights in the future.