Gymnotus is the among the most species-rich group of electric knifefishes (Gymnotiformes

Gymnotiformes

The Gymnotiformes are a group of teleost bony fishes commonly known as the Neotropical or South American knifefishes. They have long bodies and swim using undulations of their elongated anal fin...

) found in the Amazon

Amazon Basin

The Amazon Basin is the part of South America drained by the Amazon River and its tributaries that drains an area of about , or roughly 40 percent of South America. The basin is located in the countries of Bolivia, Brazil, Colombia, Ecuador, Guyana, Peru, and Venezuela...

. Some Gymnotus species live in the leaf litter and root tangles of river banks. Other species are specialized to live on floodplains within the rootmats of floating meadows. Several species are broadly adapted to live in both of these habitats. Gymnotus are nocturnal predators feeding on insect

Insect

Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

s, crustacean

Crustacean

Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...

s, and other 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...

. They generate weak electric field

Electric field

In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...

s used in locating objects, and also for communication in which the males court females using stereotyped electrical "songs".

Small scales are always present on this fish. The mouth is superior, meaning it is turned upwards. The anal fin terminates at a point near the tip of the tail. Species of Gymnotus reach up to about 100 cm in length. This is the most widespread genus of the order Gymnotiformes, extending from southern Mexico

Mexico

The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...

 to Argentina

Argentina

Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...

. They also occur in Trinidad

Trinidad

Trinidad is the larger and more populous of the two major islands and numerous landforms which make up the island nation of Trinidad and Tobago. It is the southernmost island in the Caribbean and lies just off the northeastern coast of Venezuela. With an area of it is also the fifth largest in...

.

Species

• Gymnotus anguillaris Hoedeman, 1962.
• Gymnotus arapaima Albert & Crampton, 2001.
• Gymnotus ardilai Maldonado-Ocampo & Albert, 2004.
• Gymnotus bahianus Campos-da-Paz & Costa, 1996.
• Banded knifefish
  Banded knifefish
  The Banded knifefish is a knifefish native to South America.-Physical characteristics:The banded knifefish is gray fish with a band of large black spots outlined with yellow on either side. they can get up to 60 cm long.-Range and habitat:The banded knifefish lives in lakes and streams in...
  
  , Gymnotus carapo Linnaeus
  Carolus Linnaeus
  Carl Linnaeus , also known after his ennoblement as , was a Swedish botanist, physician, and zoologist, who laid the foundations for the modern scheme of binomial nomenclature. He is known as the father of modern taxonomy, and is also considered one of the fathers of modern ecology...
  
  , 1758.
• Gymnotus cataniapo Mago-Leccia, 1994.
• Gymnotus chimarrao Cognato et al., 2007
• Gymnotus choco Albert, Crampton & Maldonado, 2003.
• Gymnotus coatesi La Monte, 1935.
• Gymnotus coropinae Hoedeman, 1962.
• Gymnotus curupira Crampton, Thorsen & Albert, 2005.
• Gymnotus cylindricus La Monte, 1935.
• Gymnotus diamantinensis Campos-da-Paz, 2002.
• Gymnotus esmeraldas Albert & Crampton, 2003.
• Gymnotus henni Albert, Crampton & Maldonado, 2003.
• Gymnotus inaequilabiatus (Valenciennes
  Achille Valenciennes
  Achille Valenciennes was a French zoologist.Valenciennes was born in Paris, and studied under Georges Cuvier. Valenciennes' study of parasitic worms in humans made an important contribution to the study of parasitology...
  
  , 1842).
• Gymnotus javari Albert, Crampton & Hagedorn, 2003.
• Gymnotus jonasi Albert & Crampton, 2001.
• Spotted knifefish, Gymnotus maculosus Albert & Miller, 1995.
• Gymnotus mamiraua Albert & Crampton, 2001.
• Gymnotus melanopleura Albert & Crampton, 2001.
• Gymnotus obscurus Crampton, Thorsen & Albert, 2005.
• Gymnotus onca Albert & Crampton, 2001.
• Gymnotus panamensis Albert & Crampton, 2003.
• Gymnotus pantanal Fernandes, Albert, Daniel-Silva, Lopes, Crampton & Almeida-Toledo, 2005.
• Gymnotus pantherinus (Steindachner
  Franz Steindachner
  Franz Steindachner was an Austrian zoologist.- Work and career :Being interested in natural history, Steindachner took up the study of fossil fishes on the recommendation of his friend Eduard Suess...
  
  , 1908).
• Gymnotus paraguensis Albert & Crampton, 2003.
• Gymnotus pedanopterus Mago-Leccia, 1994.
• Gymnotus stenoleucus Mago-Leccia, 1994.
• Gymnotus sylvius Albert & Fernandes-Matioli, 1999.
• Gymnotus tigre Albert & Crampton, 2003.
• Gymnotus ucamara Crampton, Lovejoy & Albert, 2003.
• Gymnotus varzea Crampton, Thorsen & Albert, 2005.