''Gymnotus'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

Neotropical The Neotropical realm is one of the eight biogeographic realms constituting Earth's land surface. Physically, it includes the tropical terrestrial ecoregions of the Americas and the entire South American temperate zone. Definition In bioge ...

freshwater fish in the family Gymnotidae found widely in South America, Central America and southern Mexico (

36th parallel south The 36th parallel south is a circle of latitude that is 36 degrees south of the Earth's equatorial plane. It crosses the Atlantic Ocean, the Indian Ocean, Australasia, the Pacific Ocean and South America. Around the world Starting at the Prim ...

to 18th parallel north). The greatest species richness is found in the

Amazon basin The Amazon basin is the part of South America drained by the Amazon River and its tributaries. The Amazon drainage basin covers an area of about , or about 35.5 percent of the South American continent. It is located in the countries of Bolivi ...

. They are sometimes referred to by the English name banded knifefish, although this typically is reserved for the most widespread species, '' G. carapo''. Overall ''Gymnotus'' is the most widespread genus in the order

Gymnotiformes The Gymnotiformes are an order of teleost bony fishes commonly known as Neotropical knifefish or South American knifefish. They have long bodies and swim using undulations of their elongated anal fin. Found almost exclusively in fresh water (the ...

. Although not commonly eaten by humans, some members of this genus are used locally as

fishing bait Fishing bait is any substance used to attract and catch fish, e.g. on a fishing hook. Bait items are both selected from and placed within the environment to achieve enhanced prey capture success. Traditionally, fishing baits are natural fish food ...

, and occasionally kept in aquariums.

Habitat

''Gymnotus'' occur in virtually any freshwater habitat in their range, even those with little oxygen (survives by breathing air directly from the water surface), areas affected by pollution, and for a period on land if their aquatic habitat dries out. Large species tend to live near floating vegetation along the edges of large rivers or floodplains, while smaller tend to live among leaf-litter or near banks of small streams. The genus includes both widespread and common species that occur in many different habitat types, and more restricted and rare species that occur in fewer habitats. There are species that remain in the same habitat throughout their lives, while others breed in specific habitats and spend the rest of their time elsewhere. At least as many as five species of ''Gymnotus'' may occur together in the same region and habitat.

Behavior

''Gymnotus'' species are

nocturnal Nocturnality is an animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnal meaning the opposite. Nocturnal creatures generally have highly developed sens ...

and mainly feed on aquatic

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pairs ...

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...

s, small fish and other small animals, but may also take plant material. Being

electric fish An electric fish is any fish that can generate electric fields. Most electric fish are also electroreceptive, meaning that they can sense electric fields. The only exception is the stargazer family. Electric fish, although a small minority, in ...

, they generate weak

electric field An electric field (sometimes E-field) is the physical field that surrounds electrically charged particles and exerts force on all other charged particles in the field, either attracting or repelling them. It also refers to the physical field fo ...

s used for navigation, finding prey and communicating with other individuals of their species. At least some species are highly

territorial A territory is an area of land, sea, or space, particularly belonging or connected to a country, person, or animal. In international politics, a territory is usually either the total area from which a state may extract power resources or a ...

and will react aggressively if detecting the electric field of another individual of their species, especially between conspecific males. The electric signal is species specific, and tends to differ between males and females. However, ''Gymnotus'' are not able to generate a strong electric field that can be used for incapacitating prey or enemies, like the related

electric eel The electric eels are a genus, ''Electrophorus'', of neotropical freshwater fish from South America in the family Gymnotidae. They are known for their ability to stun their prey by generating electricity, delivering shocks at up to 860 volts ...

. Nothing is known about the breeding behavior of most members of this genus, but in two species, ''G. carapo'' and ''G. mamiraua'', males make a "nest" (a depression in the bottom in the former species and within vegetation in floating meadows in the latter) and guard the young. Additionally, males of at least ''G. carapo'' will

mouthbrood Mouthbrooding, also known as oral incubation and buccal incubation, is the care given by some groups of animals to their offspring by holding them in the mouth of the parent for extended periods of time. Although mouthbrooding is performed by a va ...

Appearance

''Gymnotus'' are generally brownish with a banded pattern, but this can also be more mottled or spotted in some species. Small scales are always present on these fish. The mouth is superior, meaning it is turned upwards. The

anal fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...

terminates at a point near the tip of the tail. Like other

Neotropical knifefish The Gymnotiformes are an order of teleost bony fishes commonly known as Neotropical knifefish or South American knifefish. They have long bodies and swim using undulations of their elongated anal fin. Found almost exclusively in fresh water (the ...

, they often lose their tail due to attacks by predators or aggressive encounters with conspecifics, but they are able to regenerate it. The largest ''Gymnotus'' are up to in total length. Most species reach less than one-third that size and the smallest only around long.

Species

There are currently 46 recognized species divided into six subgenera in ''Gymnotus'': Subgenus ''Gymnotus'' ''(Gymnotus)'' Subgenus ''Gymnotus (Lamontiana)'' Subgenus ''Gymnotus (Pantherus)'' * '' Gymnotus capitimaculatus'' Rangel-Pereira, 2014 * '' Gymnotus pantherinus'' (

Steindachner Franz Steindachner (11 November 1834 in Vienna – 10 December 1919 in Vienna) was an Austrian zoologist, ichthyologist, and herpetologist. He published over 200 papers on fishes and over 50 papers on reptiles and amphibians. Steindachner describ ...

, 1908) * '' Gymnotus refugio'' Giora & L. R. Malabarba, 2016 Subgenus ''Gymnotus (Tijax)'' * '' Gymnotus cylindricus'' La Monte, 1935 * '' Gymnotus maculosus'' J. S. Albert &

R. R. Miller Robert Rush Miller (April 23, 1916 – February 10, 2003) "was an important figure in American ichthyology and conservation from 1940 to the 1990s." He was born in Colorado Springs, earned his bachelor's degree at University of California, Berke ...

, 1995 (Spotted knifefish) * '' Gymnotus panamensis'' J. S. Albert & Crampton, 2003 Subgenus ''Gymnotus (Tigre)'' Subgenus ''Gymnotus (Tigrinus)''

References

{{Taxonbar, from=Q13033659 Gymnotidae Fish of South America Freshwater fish genera Taxa named by Carl Linnaeus