Find a fish…and prey species, that acts and sounds like these. rnrnThe actual fish we have recorded underwater are nearly silent in comparison. A hydrophone is a microphone designed to be used underwater for recording or listening to underwater sound. Most hydrophones are based on a piezoelectric transducer that generates electricity when subjected to a pressure change. Such piezoelectric materials, or transducers, can convert a sound signal into an electrical signal since sound is a pressure wave.