The ampullae of Lorenzini are a sensory system that allows certain aquatic animals to perceive weak electrical fields. This network of biological receptors provides a “sixth sense” of the surrounding electrical world, a sense imperceptible to many other animals. This electrosensory system is an adaptation offering significant advantages for survival in marine environments.
Anatomy of the Ampullae
The visible component of this sensory system consists of small pores on the skin, primarily concentrated around the head, snout, and mouth of the animal. These pores are the external openings to a network beneath the skin, where each pore leads to a long canal. These canals are filled with a thick, gelatinous substance. This gel is a glycoprotein-based substance that has a high proton conductivity, one of the highest of any biological material, and acts as an excellent electrical conductor.
At the base of each gel-filled canal lies a small, bulb-like chamber containing the sensory cells, known as electroreceptors. These cells are connected to nerve fibers that transmit information to the brain. The structure functions by detecting a voltage difference between the seawater at the pore’s opening and the tissue at the base of the receptor cell. When an electric field is present in the water, it creates a voltage gradient along the conductive gel, which the sensory cells then detect and signal to the brain.
How Animals Use Electroreception
Animals with ampullae of Lorenzini use this sense for detecting prey and for navigation. All living organisms generate weak bio-electric fields from muscle contractions and nerve firings, which a predator can detect to locate prey hidden from sight. This makes it possible to find animals buried under sand or concealed in darkness. Sharks, for example, are more sensitive to electric fields than any other animal group, with a detection threshold as low as 5 nanovolts per centimeter. This sensitivity allows them to pinpoint the precise location of a hidden flounder or a ray on the seafloor by sensing the weak electrical field its body produces.
Beyond hunting, this electrosensory system serves as a biological compass. Animals can use their ampullae to detect the Earth’s geomagnetic field. This ability is useful for long-distance migrations across open ocean. By sensing the magnetic field, these creatures can orient themselves and maintain a consistent direction, navigating the seas with accuracy.
Which Species Possess This Sense
The ability to sense electric fields is an ancient trait found in several groups of aquatic vertebrates. The most well-known possessors of ampullae of Lorenzini are the cartilaginous fishes, a group known as Chondrichthyes. This class includes sharks, rays, skates, and chimaeras.
While strongly associated with sharks and their relatives, this sensory system is not exclusive to them. It is also present in some species of “primitive” bony fishes, including sturgeons and paddlefish. The presence of ampullae of Lorenzini in these ancient groups suggests that electroreception evolved early in vertebrate history and has been retained in species where it offers a distinct survival advantage.