The Electric Signal
How Electric Fish Produce and Detect Electric Signals
The electric signal of an electric fish is produced by a specialized electric organ. In weakly electric fish like the Elephant Nose fish (Gnathonemus petersii), this organ is located in the tail (Kawasaki).
| Depiction of the Elephant Nose fish (Gnathonemus petersii) showing the location of teh electric organ. Image used with permission of Masashi Kawasaki |
In strongly electric fish, the electric organ is larger and can constitute a large portion of the fishes volume. The electric organ of the Electric Eel (Electrophorus electricus) makes up about 40% of the eel's body volume (Schmidt-Neilsen 2001).
Electric Signal Production: Fish that are able to produce electric signals are said to be electrogenic (Nelson Lab). The electric organ contains columns of stacked electroplates or electroplaques, cells of modified muscle that lack the ability to contract and are specialized for the generation of electric current. One face of the electroplate is smooth and covered with nerve endings, and opposite face is deeply folded. When the electric organ is inactive, both faces of the electroplate are positive on the outside and negative on the inside, so that the difference in potential from one side to the other is zero. To generate a signal, the brain sends an electric signal to the first electroplate in the column, which depolarizes the innervated electroplate surface. This creates a voltage across the electroplate cell which depolarized the adjacent electrocyte, generating more current and passing the depolorization wave along the electroplate column.Essentially, the stacked electroplates act as a series of batteries. The charge genearted from these connected "batteries" is released into the surrounding water for electrocommunication or electrolocation, or into the body of another animal to stun or kill them (Schmidt-Neilsen 2001).
| Animation showing EOD signal production. When the organ is resting, the electroplates are uniformly charged. At the introduction of an electric signal from the brain, the smooth innervated side of the electroplate depolarizes, creating a voltage. The wave continues along the electroplate column, creating a total charge that can be very powerful. Image used with h permission of Masashi Kawasaki. |
Electric Signal Reception: In addition to producing signals, electric fish can receive and interpret electric signals either produced by themselves or by other fish. Fish that can detect electric signals are electroreceptive (Nelson Lab). Signals are detected by special receptors located on the skin of the fish. There are two kinds of receptors: tuberous and ampullary. Tuberous electroreceptors respond to high frequency signals (several hundred hertz) and are specific to electric fish. Ampullary electroreceptors are found in both electric and non-electric fish, and respond to much lower frequencies (Schmidt-Neilsen 2001).
This website was created as a part of a class project in the Animal Physiology Class at Davidson College.