gymnotiforms

Gymnotiformes, commonly called gymnotiforms or electric knifefishes, are an order of neotropical freshwater fishes native to Central and South America. They are typically slender, elongated fishes with a head-tapered body and a long anal fin that drives forward movement by undulating waves. A hallmark of gymnotiforms is their ability to generate weak electric fields using specialized electric organs derived from muscle tissue that run lengthwise along the body and tail.

These electric organs discharge continuous electrical signals, producing an electric organ discharge (EOD) that surrounds the fish. EODs function in active electrolocation — enabling the animal to detect objects and prey through distortions in the field — and in intraspecific communication. EOD frequency and pattern are often species- and individual-specific and can be modulated during social interactions; in some species, males alter their EOD during courtship.

Dietary habits vary but many gymnotiforms feed on small invertebrates, crustaceans, and sometimes small fish, typically foraging in dim light or turbid waters. They inhabit a range of freshwater habitats, from rivers and streams to floodplain lakes, often occupying sheltered benthic or mid-water microhabitats.

Taxonomically, gymnotiforms include several families and many species, such as Gymnotus (the common knifefishes), Eigenmannia (glass knifefishes), and Apteronotus (ghost knifefishes). A related, well-known member of the broader group is Electrophorus electricus, the electric eel, which can generate stronger shocks. Because of their distinctive electric signaling, gymnotiforms are frequently studied in neurobiology and sensory ecology as model organisms for understanding electroreception and neural control of communication signals.