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What is a Knifefish?

Kasey James
Kasey James

A large fish shaped like an everyday knife is commonly known as the knifefish. This fish has an elongated look and are kin to another group of fish called eels. Most knifefish come from the fresh waters of South America, but a few species live in Africa and southeast Asia.

The knifefish fits into two orders, the Gymnotiformes and Osteoglossiforms. These orders are made up of several sub-families, including Apteronotinae, Electrophorinae, Gymnotinae, Hypopominae, Rhamphichthyinae and Sternopyginae. These families inhabit different parts of South America in the fresh waters. There are several species of South American knifefish that typically range from 8 to 24 inches (20 to 61 cm) in length.

The majority of knifefish live in the fresh waters off South America.
The majority of knifefish live in the fresh waters off South America.

Some knifefish live in Africa and southeast Asia. These are from the Notopteridae family. This family is similar to the South American families except that the caudal and anal fins are merged, showing a larger fin. These species range from 12 to 40 inches (30.5 to 101.6 cm) in length.

Many of these knife-shaped fish from South America can be raised in a home aquarium. The ones that can mature in a tank include the black ghost, brown ghost, speckled, banded, green and glass variations of knifefish. The fish from Asia and Africa that can be raised in an aquarium include the clown knifefish, Asian knifefish and African knifefish.

These fish can be fairly large, so they need to live in a tank that can hold at least 90 gallons (341 l). Knifefish prefer to be in a darker space with plenty of rocks and plants under which they can hide. They can be injured by sharp-edged rocks, though, because they do not have scales.

Most of these fish are nocturnal, but some can be active during the day. When being raised in a tank, they will feed in the dark. They eat live food such as insect larvae, worms and crustaceans as well as chopped meat. Some of these fish will jump out of the tank if the tank lid is not securely closed.

Knifefish can be known to be aggressive toward each other or toward fish of a smaller species, and they will eat smaller fish in the wild or in captivity. In a home aquarium, they do best with fish of similar size and growth. They usually are not aggressive toward fish that are medium to large in size. Most species of knifefish live three to seven years, with a few species living to be 10 years old.

Frequently Asked Questions

What is a knifefish and where can it be found?

Knifefish are a distinctive group of fish known for their elongated, blade-like bodies and the absence of dorsal fins. They inhabit freshwater environments in Central and South America, thriving in rivers, streams, and flooded forests. Their unique body shape allows them to navigate the complex underwater structures of their habitats with ease.

How does a knifefish navigate and move in the water?

Knifefish navigate using a specialized organ called the electric organ, which emits weak electric fields to sense their surroundings and communicate with other knifefish. They move through the water with undulating movements of their anal fin, which runs along the underside of their body, allowing for precise and stealthy movement in their murky aquatic habitats.

What do knifefish eat and how do they find their food?

Knifefish are generally nocturnal predators, feeding on insects, crustaceans, and small fish. They locate their prey primarily through electrolocation, a process where they detect disruptions in their electric field caused by other organisms. This method is highly effective in the dark or turbid waters where visual cues are limited.

Are knifefish social or solitary creatures?

Most knifefish species are considered to be solitary, especially when it comes to hunting for food. However, some species exhibit social behaviors, such as the Black Ghost Knifefish, which can be found in small groups. Their social interactions are often facilitated by their electric organs, which they use for communication.

Can knifefish be kept in home aquariums, and if so, what are their requirements?

Yes, certain knifefish species, like the popular Black Ghost Knifefish, can be kept in home aquariums. They require large tanks with plenty of hiding places and a soft, sandy substrate to mimic their natural environment. The water should be kept clean and well-filtered, with a stable temperature suitable for tropical fish. It's important to research the specific needs of the knifefish species you're interested in keeping.

What is the conservation status of knifefish, and are they facing any threats?

The conservation status of knifefish varies by species. While many species have not been evaluated for the IUCN Red List, habitat destruction, pollution, and overfishing pose threats to their populations. Some species are more vulnerable due to their specific habitat requirements, making them sensitive to environmental changes and human activities.

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    • The majority of knifefish live in the fresh waters off South America.
      By: Iryna Volina
      The majority of knifefish live in the fresh waters off South America.