Clicks and buzzes on coral reefs suggest that there is communication by sound under the sea. Who is speaking? And what might they be saying? Dr Anjani Ganase discusses research on sounds emitted by fish.
For life in the ocean, water becomes the ideal medium for communicating by sound compared to air. Sound travels five times faster and much further distances in water than it does in air. When it comes to other communication methods, by comparison, the use of smell (olfactory) or sight is limited to much smaller spaces. While this may not be obvious on the brightly lit shallow, buzzing coral reefs, for most of the ocean that is in low light or no light conditions, sound becomes very important. Most studies of sound communication listen to large marine mammals, who use sophisticated sounds patterns to communicate with each other and to navigate distances of hundreds of kilometres. Less understood are the sounds used by fish to communicate with each other at close range, or whether they can communicate over long distances.
It is well understood that while most fish can 'hear' underwater, many appear to not produce sounds, at least not with the intention of communication. However, there are a few families of fish species, such as ray-finned fishes and many deep-ocean species that occur at depths or in darkness where visual cues are non-existent. Scientists are slowly uncovering the world of fish communications.
When it comes to talking fish, it is very difficult to connect the sounds to the fish as well as to the physical mechanism used in sound creation. In some scenarios, the scientists may be lucky to observe a fish carrying out a specific behaviour, such as colour changes or by dipping the body, that go along with sound creation during spawning or mate calling activities. Often, the production of sounds is not associated with any obvious physical or behavioural changes in the fish. In the dark, the need for light by scientists seeking to identify the sounds often causes the fish to flee. Many fish species are also observed in captivity, but tank environments also skew the information because of reflecting sound waves. Nonetheless, scientists have studied quite a few species in details including the catfish, while toadfish are known to be the loudest communicators.
There is also minimal understanding of the mechanisms that create the sounds. Sound is made mostly using specialised sonic muscles (sound producing muscle attached to the swim bladder) that vibrate against the bladder like a drum. Alternatively, sound can be made by rubbing bony elements together. This is how catfish and damselfish can make such high shrill sounds, similar to that of insects, by rapidly moving their jaw bones.
Most studies are conducted in shallow water environments and of the fishes studied, many can make a large variety of sounds and most occur at very low frequencies of less than 1000 hertz. Fish can carry out some tonal sounds through continuous muscle contractions. For the most part, owing to the wide variety of
