Learn About Electric Fish
Electric organs and electroreceptors
Electric organs evolved independently in several groups of fishes: Torpedo rays, electric skates (Raja), strongly electric catfish (Malapterurus), stargazers (Astroscopidae), South American knifefishes (Gymnotiformes), and African mormyriform fishes. In most electric fish, the electric organ is derived from muscle. Electrocytes, the cells that comprise muscle-derived electric organs, retain some of the electrical properties of muscle, but have lost contractile properties.
Our laboratory studies the ghost knifefish (family Apteronotidae), which are exceptional in that their electric organs are derived from nervous tissue, rather than muscle. The electric organ of ghost knifefish consists of specialized peripheral nerves containing large axons that have no target. The axons in the electric organ synchronously and rhythmically produce action potentials to generate an oscillating electrical field around the fish.
The ability to detect bioelectric fields is a primitive trait in vertebrates. Electroreception was lost in the teleost fishes and then independently re-evolved in several different teleost lineages. Electrical fields are detected with specialized electroreceptor organs in the skin. Electroreceptors in species that lack electric organs (e.g., sharks, lampreys, catfishes) are ampullary receptors, specialized for passively detecting the very weak bioelectric fields produced by other organisms. To detect such weak electric fields, ampullary receptors must be very sensitive. As a consequence of their extreme sensitivity, ampullary receptors integrate signals over time, and respond primarily to low-frequency signals.
Weakly electric fish (South American gymnotiform knifefish and African mormyriform fish) have also evolved other classes of receptors (e.g., tuberous receptors in gymnotiform fishes) that can detect high frequency electrical signals and are specialized for active electrolocation and communication (see section on the functions of electric organ discharges below).