The Ampullae of Lorenzini are specialized sensory organs that grant sharks and other cartilaginous fishes the ability known as electroreception. This adaptation allows these animals to perceive the weak electrical fields naturally present in their aquatic environment. This sensitivity plays a significant role in both how elasmobranchs, such as sharks and rays, hunt and navigate the vast ocean.
Physical Structure and Location on the Shark
The ampullae of Lorenzini are visible externally as tiny pores concentrated primarily on the shark’s snout and the underside of its head. These pores open into a complex subcutaneous network of jelly-filled canals that penetrate the skin. The number of these organs varies greatly, with some species possessing several thousand ampullae across their facial region.
Each pore connects to a long, narrow canal that terminates in a small, bulb-like structure called the ampulla. This bulb contains the sensory cells, which are the biological transducers of the system. The canals are filled with a specialized, highly conductive glycoprotein-based gel that efficiently transmits electrical potential from the seawater to the sensory cells deep within the ampulla.
The Mechanism of Electroreception
The ampullae function by detecting minute differences in electrical voltage between the external pore and the internal base of the sensory canal. The long, conductive canal effectively amplifies the voltage gradient across its length. When an electrical field is present, the resulting potential difference causes a change in the electrical polarity across the membrane of the sensory cells. These specialized electroreceptor cells, which are modified hair cells, respond to the electrical change by triggering a nerve impulse that is transmitted to the shark’s brain. This system is extraordinarily sensitive, allowing sharks to detect electrical fields as weak as 5 nanovolts per centimeter. This extreme detection threshold allows the shark to sense the faintest low-frequency electrical signals, typically below 50 Hertz, that permeate the water.
Utilizing Electrical Fields for Predation and Navigation
Predation
The primary application of this electric sense is in the final phase of predatory attacks, especially when other senses are rendered ineffective. All living organisms generate faint bioelectric fields as a byproduct of muscle contraction, nerve activity, and ion exchange during respiration. Sharks use the ampullae to detect these weak direct current (DC) fields emitted by potential prey. A common example involves prey such as flounders or rays that bury themselves under the sand to hide from visual detection. Despite being obscured, the animal’s gill movements and heart muscle contractions create an electrical field that radiates through the surrounding water. The shark can use its array of ampullae to precisely locate the buried creature, switching from visual or olfactory cues to electroreception for the final strike.
Navigation
Electroreception is also hypothesized to function as a mechanism for long-distance orientation. As a shark swims through the Earth’s geomagnetic field, its movement induces weak electrical currents within its body and the surrounding conductive seawater. The ampullae of Lorenzini are sensitive enough to detect these induced currents, which can provide directional information. This allows the shark to use the geomagnetic field as a biological compass, helping it maintain a bearing and navigate during extensive seasonal migrations across entire ocean basins.
Evolutionary Context and Other Electroreceptive Animals
While the ampullae of Lorenzini are most famously associated with sharks, this electrosensory capability is a widespread trait among aquatic vertebrates. All cartilaginous fish, including rays and chimaeras, possess this sensory system. Electroreception is also found in several basal groups of bony fishes, such as sturgeons, paddlefishes, lungfishes, and bichirs. These organs evolved from the mechanosensory lateral line system, an ancestral trait present in the earliest vertebrates. Most modern bony fishes and all terrestrial amniotes lost this sense during their evolutionary development. However, electroreception has re-evolved independently in a few unique lineages, most notably in the semi-aquatic monotreme mammals like the platypus. The platypus possesses electroreceptors on its bill that are structurally distinct from the ampullae of Lorenzini, illustrating convergent evolution toward this aquatic sense.