(NaturalNews) Much like land animals, fish also use sounds to communicate with each other and even with predators, according to a study conducted by researchers from the University of Auckland, New Zealand, and presented at a conference of the New Zealand Marine Sciences Society.
Shahriman Ghazali and colleagues used underwater microphones and other instruments to detect water vibrations produced by New Zealand fish kept in tanks in his laboratory. The special instruments were required because the human ear is not designed to hear sound underwater. The researchers found that many fish produced sounds such as chirps, grunts and pops.
"All fish can hear, but not all can make sound -- pops and other sounds are made by vibrating their swim bladder, a muscle they can contract," Ghazali said.
One of the most vocal species was the gurnard, which vocalized almost continuously and was capable of a wide range of sounds. Bigeyes produced a regular popping sound, and damselfish appeared to produce sounds when they felt threatened by other fish, perhaps to scare them off.
In contrast, cod were silent except when spawning.
"The hypothesis is that they are using sound as a synchronization so that the male and female release their eggs at the same time for fertilization," Ghazali said. "Outside spawning season, you won't hear a sound from them."
Goldfish were completely silent, and New Zealand crayfish were actually quieter than the researchers had expected. While divers have reported hearing popping sounds from New Zealand crayfish and other species have been known to make a guitar-like sound, the researchers detected no sounds from the specimens in his lab.
The researchers now hope to test their hypotheses for the function of the fishes' sounds.
"We are 99 percent sure they are fish sounds," Ghazali said. "Now we want to find out what the sounds mean."