Sound is incredibly important to a person. It is the means by which most of us communicate, and most things in our society are built around the premise that we can hear.
We have built languages and communication around this sense, created whole new areas of art using it,
and even rely on it to determine differences in mood or emotion without using words – for example, grunts of acceptance or signs of exasperation.
This isn’t only true for humans. Monkeys, birds, wolves, and even crickets use sound as a means to communicate, as do many other animals and have done for thousands of years.
However, sound as we know and experience it is purely a land-based phenomena, because we are land-based animals.
But what about the creatures that live in the sea, particularly fish. Fish have never once made the evolutionary leap onto land and spend their time completely submerged underwater.
So, can they experience sound? Would it have any reason to develop in the first place? In this article,
we will take a closer look at fish and discover whether or not the fish of the oceans are listening or not.
Hearing And Fish
Before we get on to the question of this article, we will briefly touch upon hearing itself and how we clarify it.
Our auditory sense or hearing is the body’s way of perceiving sounds through a specially adapted organ, in the case of humans and most mammals this organ is the ear.
We do this by detecting vibrations in the world around us. These vibrations cause changes in pressure of the world around us, which we then pick up on,
for example the small force of a twig snapping will ripple through the molecules of the air and that ripple’s effect is what we hear.
In most vertebrates, including humans, these vibrations are picked up by the ear and converted into neural impulses, which are sent to the brain which then interprets the message.
It’s like a game of telephone inside your brain, except the players are almost never wrong. In fact, hearing works similarly to touch,
in that they both need a sensitivity to the molecules in the world around them, rather than taking something inside the body to interpret something.
So, now we have the basic definition of hearing, what about fish? Can they hear? Yes, fish can in fact hear, though it is a different way of hearing than humans.
In humans, we have three distinct parts that transmit and amplify the sounds we hear: the outer ear, the middle ear, and the inner ear.
But, fish don’t have external ears, instead only having inner ears that are called otoliths. These otoliths are made of calcium carbonate, which makes them very dense, even denser than their own bodies.
This is so that bone conduction can happen. Bone conduction is a method of hearing whereby vibrations are transmitted to the inner ear by the bones of the skull of the animal,
allowing for smaller ear canals while not impeding hearing.
Most creatures that live in water use some form of bone conduction to hear, as it is harder to localize sound and the hearing threshold is reduced thanks to the water distorting the vibrations.
With bone conduction, all the vibrations have to do is hit the body, and the animal can hear what caused them fairly easily.
Even with all this, you’ve probably realized that hearing in water is not easy. The water makes it hard to get a clear picture of where the sound came from,
and the system is not as intricate or refined as those developed on land, thanks to our air’s low mass. Due to this,
there is a second system that fish have developed for detecting vibrations and movement. That is the lateral line system.
This system can detect changes in pressure, different vibrations, and even movement from other animals in the water through the use of hair cells which are sensitive to motion in the water.
Use of this system allows fish to orientate themselves in the water and know where they are at any moment, in a similar function to the spatial orientation systems that aircraft use.
This system is incredibly important to a fish’s survival and is used by predator and prey alike,
for tracking prey in the water by trails they left when fleeing or to manage schooling and herd behavior when a school of fish is under attack.
The lateral line system is so useful in water that even amphibians have developed their own version of it for their larvae, and some even keep the system into adulthood.
This system is used in conjunction with a fish’s hearing in order to localize sound and give the fish pinpoint accuracy to ascertain where it is coming from.
How Good Is A Fish’s Hearing?
Hearing is critical to a fish, and they are far better at hearing underwater than us or any other land-dwelling creature; some sharks have been known to hear a sound from miles away.
However, the range that fish hear at is much lower than most mammals. There is a lot of speculation as to why this could be,
but realistically fish don’t need to hear as well or at the range that we do, especially since they have a secondary system that picks up on what their ears can’t.
For comparison, humans can hear between 20 and 20,000Hz and fish can at most hear up to 3,000Hz from just their ears, not with their lateral line system.
Even with the lateral line system, having hearing seems like a disadvantage for fish, but you should also remember the environment fish live in.
On land in the open air, we can take full advantage of using complex systems for hearing, cetaceans have a fully aquatic ear to aid them that required a lot of time and energy to develop,
but for fish they already have a complex system in the lateral line system to help their hearing, something mammals don’t have.
To develop the ear would be nothing but a hindrance at this point, when they have already perfected a two-organ system that helps them hear or at least detect vibrations perfectly in their environment.
So, fish can hear and the ways that they have overcome the problems of their environment to make hearing useful is incredible.
Maybe they don’t do it in the same way as we mammals do, and maybe understanding how the two systems their body’s use is a bit difficult for our brains to comprehend.
Yet, that should not stop us marveling at the ingenuity of the solution nature provided the fish over long years of evolution to achieve a perfectly functional auditory processing network inside their own bodies.
Considering the vast difficulties that life faces when living in the ocean, it must be comforting for a fish to know that it will have a great way to listen for potential threats without worrying about water getting in the way.
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