Lateral line
A line of sense organs along each side of a fish that feels movement and pressure changes in the water.
Also: lateral line system, neuromasts
The lateral line is usually visible as a thin line of pores along each flank, running from the head to the tail. Under the pores lie canals with clusters of hair cells, called neuromasts, that bend when the water moves. With it a fish feels currents, a predator approaching, prey struggling and the movements of its neighbours in a school, even in total darkness. Blind cave fish find their way almost entirely by it. Scale counts along the lateral line are a common way to identify species.