What body feature lets sharks detect weak electric fields in seawater?

The ampullae of Lorenzini let sharks detect weak electric fields in seawater.

These organs are small, jelly-filled canals concentrated around a shark’s head and snout. They connect to pores on the skin and respond to tiny voltage differences produced by the muscle activity and nerve signals of nearby animals.

Electroreception is especially useful when prey is hidden under sand or when visibility is poor. A shark can use the sense during the final stage of an attack, when smell and other signals may narrow the search but cannot precisely reveal the prey’s location.

The organs are named after Stefano Lorenzini, who described the structures in the seventeenth century. Many other cartilaginous fishes, including rays and skates, also possess ampullae of Lorenzini. They do not generate electricity; they detect electrical signals already present in the environment.