FISH SENSES: HEARING
- Friendly Fins
- Nov 29, 2024
- 5 min read
Updated: Mar 8
“Why do you always say ‘as silent as a fish’?” Don’t you know we’re big chatterboxes?!”
Let's continue our journey to discover the senses of fish:
When we put our head under water, we are immediately enveloped in a new environment, apparently silent that transmits peace and tranquility... However, if we close our eyes and concentrate only on hearing, we will realize that it is not silent at all! We will hear an extremely varied range of noises, sounds and ticks! Do you know why?
Because fish have more methods of producing sound than any other group of vertebrates!
Let's start from the beginning: the sound in the water
Sound is a pressure variation that propagates in an elastic physical medium, and therefore the density of the medium determines its speed. Water is less compressible than air and therefore sound propagates much faster, this is the reason why we do not hear in the same way when our head is under water! Density also depends on pressure, temperature and salinity. Therefore, sound travels faster in warm surface waters and slower in cold and deep waters.
Our ear is not capable of fully processing sound or its direction. The auricle is unable to transmit the vibration of the sound to the middle and inner ear from where it is then converted into a nervous signal for the brain. However, we can perceive some components of the sound thanks to the bones of our skull precisely because they are denser than water.
“Just because you can’t hear the sound well doesn’t mean it’s not there…”
Fish make sounds
We make sounds thanks to the vibration of air on a membrane, in water this is not possible but fish have proven to be quite ingenious. Let's see...
They can rapidly contract a pair of vocal muscles that vibrate the swim bladder, which in addition to having a buoyancy function, greatly amplifies the sound.
They make sounds by grinding their teeth in their jaws or by grinding extra teeth lining their throats. (Like the grunt fish, pictured below!)
By percussing hard parts of the body such as bones, gill covers, pectoral fins.
They can even produce sounds by expelling bubbles with their anus! Below we will see who they are!
“Now don’t laugh!”
Hearing, how do fish hear without ears?
Until the last century, it was thought that fish did not have a sense of hearing because they do not have ears, which are essential for perceiving sound in a terrestrial environment.
“But we live in water! We don’t need ears, we have developed other very ingenious tools to listen and make ourselves heard!”
Fish have excellent hearing: they perceive both infrasound (from 50 hertz) and high-frequency sounds up to 30,000 hertz (unlike us who can hear from 20 to 20,000 hertz). Let's see some examples in the graph below:
They are also able to perceive the direction of sounds and distinguish between sounds coming from above/below and left/right.
Through the “Weber Bones”
These small bones derive from modified portions of the first 4 vertebrae just behind the skull of fish. Their function is to conduct and amplify sound waves in a very similar way to the small bones of the middle ear in mammals (stapes, incus, hammer).
They are typical of a particular order of fish: the Gymnotiformes, to which carp and electric eels belong, for example.
“We probably invented this specialized hearing apparatus, and you Earthlings then managed to adapt it to life on dry land!”
Through the lateral line
It is a line that runs from the snout to the tail, on both sides of the fish. It is rich in mechanical receptors that allow it to detect low-frequency waves. This is very useful in fish that live in large schools.
“Thanks to the sideline, we can all swim very close together but without colliding because we can perceive the position of our teammates next to us!”
Using sound
Searching for food
The ability to distinguish the origin of a certain noise is very useful for hunting or escaping!
This is why fishing is not so easy, because the fish perceive the presence of the fisherman on the boat!
Communication
Fish communicate with each other by making sounds and listening to them accordingly. What do they have to say to each other?
Fish have a lot of things to tell each other: they have to defend their territory, they have to court each other, they have to look for their partner, they have to compete with potential rivals. To do this they emit the most varied sounds: from grunts to thumps, from whistles to moans, each with a specific function.
“So we’re big chatterboxes but you can’t hear us!”
At the moment this branch of science is still developing, but thanks to sophisticated instruments such as hydrophones it is making great strides.
“Who knows, maybe one day you will even be able to understand what we say to each other!”
Among the most chatty families are the Scienidae, the Gobidii, the Serranidae, which include both Mediterranean and Atlantic species, both tropical and freshwater.
The curiosities do not end here, however, pay attention to the case of the herring!
Both Atlantic and Pacific herrings have a communication, how can I say, flatulent! They are able to expel bubbles from the anus probably produced by the swim bladder. The production of these squeaking sounds probably has a social function as the production is greater when the herring schools are more populous.
Migration
Climate conditions are always changing, think of currents, tides, wave motion. These phenomena generate noises, more precisely environmental infrasounds: such as surf on rocks, beaches and submerged reefs. Many migratory fish are able to perceive infrasounds up to a single hertz and use this acoustic information to orient themselves during migration.
“They can be considered similar to the astronomical information used by migratory birds!”
Underwater noise generated by humans
Man at sea generates many noises that cause disturbance and damage, even permanent, to its inhabitants.
The noise produced by compressed air cannons used in oil exploration generates low-frequency, high-intensity sounds. This causes permanent damage at the cellular level to the delicate hair cells that line the internal auditory system of fish.
Sonar causes devastating effects on the life of cetaceans (which we will see in another article)
We ourselves, when we dive, snorkel or simply bathe, produce noises! We will not cause harm to the fish but they will surely hear us!
“Especially when you blow all those bubbles out of your mouth! You make a lot of noise but you’re so funny!”
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