They use hydrophones, underwater microphones that convert sound waves in the water to electrical signals. These signals can be converted back to audio through speakers for human ears to hear, recorded to tape for later study, and analysed by instruments. But don't plan on dropping a hydrophone into the water and expect to be greeted by a cacophony of fish noises. For the most part, fish are a quiet lot. Listen to the fish cluck, purr, knock and more.
Fish speak out when they have something to say.
The noise could startle the predator long enough to let go of its prey, allowing for a quick getaway. In the worst-case scenario, for the predator, that is, the alarm call could attract competitors that may steal its meal, or even worse, an even bigger predator looking for a hearty meal. Prime spawning spots are like prime real estate. These choice spots are usually claimed by the most aggressive males. Some fish species use sound to chase away submissive males that get too close to their territory.