The Snakeheads are members of the freshwater

Fresh Water

Fresh Water is the debut album by Australian rock and blues singer Alison McCallum, released in 1972. Rare for an Australian artist at the time, it came in a gatefold sleeve...

 perciform fish

Fish

Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

 family Channidae, native to Africa

Africa

Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...

 and Asia

Asia

Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...

. These elongated predatory fish

Predatory fish

Predatory fish are fish that predate upon other fish or animals. Some predatory fish include perch, muskie , pike, walleye, salmon.Levels of large predatory fish in the global oceans are estimated to be about 10% of their pre-industrial levels...

 are distinguished by a long dorsal fin

Dorsal fin

A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...

, large mouth and shiny teeth. They breathe air with a suprabranchial organ, a primitive form of a labyrinth organ. There are two extant genera

Genera

Genera is a commercial operating system and development environment for Lisp machines developed by Symbolics. It is essentially a fork of an earlier operating system originating on the MIT AI Lab's Lisp machines which Symbolics had used in common with LMI and Texas Instruments...

, Channa

Channa

Channa is a genus of the Channidae family of snakehead fishes. This genus contains about 29 species, but the most well known are probably northern snakehead and the giant snakehead . Channa has a wide natural distribution extending from Iran in the West, to China in the East, and parts of Siberia...

 in Asia, and Parachanna

Parachanna

Parachanna is a genus of the Channidae family of snakehead fishes. Species of Parachanna are found in tropical Africa.-Species:* African snakehead, Parachanna africana* †Parachanna fayumensis * Brown snakehead, Parachanna insignis...

 in Africa, consisting of 5-6 species.

They have become notorious as invasive species

Invasive species

"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....

, to the extent of becoming a byword for monster in popular culture.
The size of the snakehead species differs greatly.