Gymnotus

Gymnotus is a genus of neotropical freshwater fishes in the order Gymnotiformes, commonly called knife fishes or electric knifefishes. They belong to the family Gymnotidae and are among the more widespread genera in tropical South America.

They have elongated, eel-like bodies with small heads; no pelvic fins; and the dorsal and anal fins extend along much of the body, forming a continuous undulating ribbon used for propulsion. Growth lengths vary by species, commonly tens of centimeters up to near a meter.

All Gymnotus species possess specialized electric organs derived from muscle, producing continuous, low-voltage electric discharges. The signals function in electrolocation and social communication, especially in turbid, cluttered waters. Discharges are non-damaging to humans but may startle.

Gymnotus is native to tropical freshwater systems of South America, including large river basins such as the Amazon, Orinoco, and La Plata drainages. They inhabit slow-moving rivers, floodplains, swamps, and densely vegetated waters.

Behaviorally, Gymnotus species are primarily nocturnal and bottom-dwelling. They prey on benthic invertebrates, small fish, and other aquatic organisms, using their electric sense to locate hidden prey.

Reproduction biology varies among species and is not well documented for all members of the genus. The group comprises multiple described species over the 19th–21st centuries, with Gymnotus carapo among the widely recognized examples.

Conservation status varies by species; threats include habitat degradation, pollution, and habitat modification, with many species listed as data-deficient. Research on their ecology and electric signaling continues to illuminate how these fishes navigate and communicate in turbid freshwater environments.