Anyone who dives below the surface assumes that the underwater world is silent simply because humans have difficulty hearing in that medium. Science has shown that the opposite is true. A moving school of bait fish sends out sound waves. The noise of a tackle box scraped along the deck of a boat is echoed through the water. Footsteps along the bank send vibration into the water.
Some fish can hear the sound made by a worm wriggling into the bottom.
Fish have become adept at detecting and reacting to these various sounds that signal food or danger. Humans and other mammals respond to sound also. Behavior scientist have demonstrated that dogs and other mammals respond to a bell or light prior to eating and begin salivating before the food arrives. Humans respond to a siren or a horn that is honked, because we associate those sounds with danger and caution. When a fish is injured or its normal swimming impaired, it gives off distress vibrations.