What is the spiracle of a fish?

The spiracle of a fish is a small, often reduced, opening located behind the eye, primarily seen in some species of cartilaginous fish, like rays and skates. It serves as an additional respiratory structure, allowing these fish to take in water for respiration while they are resting on the sea floor or when their mouths are covered by sediment. In some species, spiracles can also play a role in sensing the environment.