The ampullae of Lorenzini
Water ‘absorbs’, carries and transports everything it comes into contact with. Grind some coffee beans, pour some hot water on it and the water changes color, scent and smell. When you drink it, you don’t perceive it as being water carrying information it received from the coffeebeans.
Water carries light and sound as well. Water surfaces tend to reflect rather than absorb sound waves, which can lead to sound being carried over longer distances. Additionally, temperature gradients in water (for example near the surface or in thermoclines) can cause refraction, bending sound waves and extending their range. Sound travels faster in water than in air. The speed of sound in water is approximately 1,482 meters per second (m/s), compared to 343 m/s in air. Due to its higher density, water allows sound waves to travel longer distances without significant attenuation (loss of energy). Water particles are closer together, enabling more efficient transmission of vibration energy.
Cartilaginous fish such as sharks, rays and chimaeras and bony fishes such as lungfish, sturgeon and reedfish, have sense organs able to detect electric fields. These sense organs are electroreceptors called ampullae of Lorenzini.
Stefano Lorenzini
Stefano Lorenzini (c. 1652), was a medical doctor, surgeon and an ichthyologist. He studied sharks (did you know sharks like to be hugged?) and rays and discovered their sense organs located in the front of their heads, that were filled with a jelly-like substance. His study ‘Osservazioni intorno alle torpedini’ was published in 1678. The ampullae are pores in the skin directly connected to the nerves. These mucus-filled pores are connecting pores in the skin to sensory bulbs. Later this mucus-like substance was described as a collagen jelly. Nowadays we can create this jelly-like substance, called a hydrogel. The collagen jelly that fills the ampullae canals has one of the highest proton conductivity capabilities of any biological material.
Sensory ability
Although the ampulla are named after Lorenzini, their function was not understood until the 1960s. The lateral line system, the fish scales being a big part of it, is ancient and basal to the vertebrate clade. Lateral lines play an important role in schooling behavior, predation and orientation. The sensory ability is achieved via modified epithelial cells, known as hair cells, which respond to displacement caused by motion and transduce these signals into electrical impulses via excitatory synapses. This makes it possible to detect electric fields in the water, allowing the fish to navigate and find prey in their environment.
All animals, and humans, produce an electrical field caused by muscle contractions; electroreceptive fish may pick up weak electrical stimuli from the muscle contractions of their prey. The sawfish has more ampullary pores than any other cartilaginous fish, and is considered an electroreception specialist.
The ampullae
Each ampulla is a bundle of sensory cells containing multiple nerve fibres in a sensory bulb in a collagen sheath, and a hydrogel-filled canal (the ampullengang) which opens to the surface by a pore in the skin. The gel is a glycoprotein-based substance with the same resistivity as seawater, and electrical properties similar to a semiconductor. As magnetic and electrical fields are related, magnetoreception via electromagnetic induction in the ampullae is possible. Magnetoreception may explain the ability of cartilaginous fish to form migratory patterns and to identify their geographic location. Many birds can detect the Earth’s magnetic field as well and use it to determine their latitude and longitude.
In 2019, a study was published showing that humans also have a geomagnetic sensory system. As of 2024, according to mainstream history and mainstream science humans have known for 350 years that sharks and rays have sensory organs fueled by a jelly substance, for 64 years how fish are able to detect changes in magnetic fields based on electrical stimuli, but only for 5 years about human magnetoreception. Interesting topic to follow!
Back to fish. Or rather: to their ampullae wherein there are supporting cells that fill the canals and produce the collagen jelly that feeds and conducts the receptor cells.
The apical (the front-facing surface of a cell, particularly in the context of epithelial cells) faces of the receptor cells have a small surface area with a high concentration of voltage-dependent calcium channels (which trigger depolarization) and calcium-activated potassium channels (for repolarization afterwards). This triggers presynaptic calcium release and release of excitatory transmitter onto the afferent nerve fibres. These fibres signal the size of the detected electric field to the fish’s brain. And thus the reality of cartilaginous fish is carried by a hydrogel responding to internal (f.i. composition of the jelly) and external stimuli (f.i. electrical fields) that make the fish live in its own bubble.
