Do fish have voices?

   Fish called croakers make hoarse "garrumph" sounds. The noise is caused by two muscles that beat on an air-filled sac like a drum in the fish's belly. The drumming can be heard through an instrument called a hydrophone, a sort of underwater microphone. Sometimes the fish keeps on croaking after it is caught and landed.
   Scientists recognize the noises made by several kinds of fish. But they are puzzled by certain strange groans and wails that the hydrophone often picks up. They don't yet know what water animal makes these weird sounds.

croaker, the fish who sings