Weakly Electric Fish
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Electrogenesis is the ability of certain animals to generate an external electric field. This ability has been known (albeit not understood) since antiquity, as in certain animals the electric current is strong and serves as a weapon, and was therefore experienced by fishermen as a tickling, numbing or painful sensation.
From left to right: 2750 BC: Mural from the Mastaba of Ti in Saqqara (ancient Egypt), depicting a fisherman pulling electric catfish (Malapterurus electricus, red arrows) out of the; 400 BC: pottery form ancient Greece depicting an electric ray (Torpedo torpedo, green arrow), known as Narkē in Greek (narkan=to numb) and as Torpedo in Latin (torpere=to paralyze); 1773 AD: John Walsh and John Hunter studied the electric organ of the Torpedo and the so-called 'Electric Eel' (electrophorus electricus) and found that it is composed of an array of electrocytes (electricity-generating cells); 1800 AD: inspired by Walsh's discoveries, Alessandro Volta invents the Voltaic Pile (the first true electric battery).
Electroreception is the ability to sense electric fields, which is quite ubiquitous in the natural world: we find this ability in insects (e.g. bees), bony and cartilaginous fishes (e.g. sharks), amphibians (e.g. Axolotl), and even in some mammals (dolphins, platypuses, and echidnae). In 1678 Stefano Lorenzini discovered the Ampullae of Lorenzini, tiny pore-like structures distributed on the fish's skin. Hans Lissman noticed in 1950 that the African knife fish (Gymnarchus niloticus) can swim equally well both forward and backward, and therefore inferred that it relies on some non-visual sensory system – which he correctly hypothesized to be electroreception. Finally, in 1960 Richard W. Murray demonstrated that the sensors in the ampulla of Lorenzini of the ray convert electric fields into neural code.
The two families of 'weakly electric' teleost fish (the South American Gymnotiformes and the African Mormyriformes) developed separately Active Electroreception: the ability to sense self-generated electric fields. The electric organ in these fish generates electric organ discharges (EODs) – weak electric pulses or waves. Objects in the close vicinity of the fish (e.g., rocks, plants, predators, or prey) distort the resulting electric field, and these distortions are sensed by an array of cutaneous electroreceptors specifically tuned the EOD, thus enabling these nocturnal fish to perceive their surroundings in the dark (Electrolocation). Electric fish also use this modality to interact with their conspecifics (Electrocommunication): courtship, aggression, etc. Since electric signals are easy to measure, generate, manipulate and model, weakly electric fish serve as a powerful tool for studying active sensing, neural sensorimotor processing, and neural coding.
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