Which sensory system detects water movement along the body in fishes?

• A. Lateral-Line System
• B. Olfactory System
• C. Auditory System
• D. Visual System

Answer: (A)

The ability to sense water movement along the body in fishes comes from the lateral line system. This network of sensory units runs along the head and along the body and contains neuromasts with hair cells. When water moves or vibrations occur nearby, the flow deflects the hair bundles in these neuromasts, opening ion channels and sending signals to the brain. This lets the fish detect the speed and direction of water currents, see nearby movements, and sense approaching prey or predators, even in darkness or murky water. The olfactory system detects dissolved chemicals, the auditory system responds to sound via the inner ear, and the visual system detects light; none of these track water movement along the body like the lateral line does.