Sharks also have an electro-receptive sensory system.
It was discovered by Marcello Malpighi (1628-1694) in 1662 and described in more detail in 1678 by his countryman Stefano Lorenzini, although he unfortunately did not recognise the function of the ampullae of Lorenzini. For a long time, the function was supposed to be sensing pressure or temperature.
Only in 1962, the Dutch scientists Dijkraaft and Kalmijn were able to prove their main function: Perception of electricity. In 2003, however, Brown showed that temperature can also be translated into electrical signal, so that sharks can also perceive temperature deviations using the electro-sensory system.
The clear electro-receptive system consists of many single pores, in particular at the underside of the head, snout and nose.
The pores are the canal openings of the ampullae of Lorenzini. The ampullae (canals) are filled with a gel that conducts even the slightest of electrical impulses with low electrical impedance. At the inner canal end, there is a cavity with electric receptors. They are able to register a potential difference over the skin. From comparing the neuronal signals from many ampoules in a skin area, a sensory signal shows the presence of a source of voltage. The receptors of the ampullae of Lorenzini enable sharks to perceive even low electrical fields of only 5 nano-Volts per cm – this corresponds to a 12V-battery at a distance of 12km!
Thus, sharks can perceive even slight muscle movement of animals over a short distance. In sea water, low electrical fields are generated in different ways. The main producers are animals producing bioelectrical fields from muscle contractions and electrochemical reactions. Cables and metal objects, however, also produce low electrical fields by galvanic reaction. In general, the perception of bioelectrical fields only works on very short distances, so that this sensory system would mainly serve to find hidden prey in the ground (e.g. for hammerhead sharks). Currently, scientists are discussing first experiments that seem to show that sharks can use the ampullae of Lorenzini for orientation using the magnetic field of the Earth and to also sense small temperature deviations.
This seems to be a true miracle sense! In contrast to common opinion, however, this is not a sense limited to sharks. Some fish have an electrical sense as well, which means they are electro-receptive, and several of them have ampullae of Lorenzini or electro-receptors.