Yet appearances deceive. For their inhabitants, the world’s oceans are certainly not silent, but full of noises and sounds. It is just that often we cannot hear them, because they are outside our range of hearing. This particularly applies to sounds made by fish. For despite common preconceptions, these animals are anything but mute. On the contrary, most fish are extremely loquacious and use a number of different sounds to communicate.

As mute as a fish? Yeah, right ...

For a long time, the belief that fish are mute hindered researchers’ interest in communication between fish. Although they had known for a relatively long time that some fish species emit acoustic signals, it was seen more as the exception than the rule. The best-known example is probably the gurnard. This reddish-brown fish lives on the seafloor, which it sifts through looking for food with its tentacle-like ventral fins. When threatened, the gurnard produces clearly audible grunting and snarling sounds.

Clown loach owners also repeatedly report peculiar clicking sounds. The popular aquarium fish seemingly like to make these sounds when feeding. As they are like loud chewing and crunching sounds, for a long time people linked them to the eating process. But in actual fact, the noises do not come from the jaw at all: the black-and-white pied fish make them with their swim bladder.

Now researchers have documented the sounds made by numerous species of fish. We can even listen to them on several Internet sites. And what comes out of our familiar speakers is utterly surprising and alien: the acoustic world of fish proves to be incredibly diverse. They click, gurgle, squeak, grunt, cheep, hum, fizzle, hiss and even quack, chirr and bark, for all they’re worth.

And they are just the most common sounds. Here too, there are exotic species and outsiders. The silver prochilodus, for instance, produces sounds during the spawning migration that vaguely call to mind the purring of a motorcycle. Many eels, in contrast, use extended infrasound for purposes of location and orientation in the water.

• Part 1: The language of fish
• Part 2: Unimagined acoustic diversity
• Part 3: Of thrummers and chirrers