A few months ago I was researching suitable fish species for a saltwater aquarium that I planned to set up and came across the Longhorn Cowfish. Immediately I fell in love with this little guy and proceeded to read up on them.
Now, I know you may be wondering what on earth this has to do with possible fish hearing, but it actually has a lot. For whilst reading I discovered that Cowfish have the capability, and use it, to make grunting sounds when they are caught. This discovery, in turn, led me to ask could another fish hear it?
Can fish hear – Fish do have the ability to hear despite not having ears. They have an Inner ear (their auditory system) and a Lateral line (their mechanosensory system). Fish use sounds like grunting, tapping and clicking to communicate which the inner ear and lateral line pick up.
It may seem like a completely crazy question to ask, especially since fish don’t have ears, or not that we can see. But, if some fish species can and do make sounds like grunting, humming, purring, and hooting, what would be the point unless they can hear it too?
As it turns out, I was right to question it, as indeed fish can hear!
The Basics Of Fish Hearing
All animals, including humans and fish, make use of the five senses; smell, taste, touch, sight, and hearing. However, we do not all make use of them in the same way or to the same degree. Humans, for example, rely largely on their ability to see, whilst fish rely heavily on their ability to hear. This is because, hearing, for a fish allows them to:
- Access information over greater distances
- Access information in all directions (3-dimensional view)
It also means they are not hindered by:
- Water Currents
- Lack of or poor light
- Other objects
Interestingly, it is believed that a fish’s ability to hear did not evolve originally in order for them to communicate. Rather, it developed in order for them to learn about their environments. Communication came later as fish gained the ability to make sounds.
How Do Fish Hear?
Over time fish have developed two separate, but yet related, sensory mechanisms to detect, locate, and understand sound. These are the:
- Inner ear (their auditory system)
- Lateral line (their mechanosensory system)
The inner ear of a fish is made up of bones known as otoliths and cilia (hair cells) which bend or displace when a sound wave hits them. This movement then sends a signal to the fishes brain where it is interpreted as a sound. Otoliths are made of calcium carbonate with the size and shape of them varying among fish species.
Unlike ears, the lateral lines can be seen if you look closely at the side of your fish. They work by using hair cells, similar to the inner ear which detects relative motion, the sound wave, between themselves and the surrounding water. The lateral line system is used more commonly to detect acoustic signals at short range; usually one to two body lengths.
Curiously, it is the lateral line system that allows fish to swim in schools. The flow of water created by each fish swimming sends signals to those beside and behind them. This, in turn, allows the fish near them to maintain their position within the fast moving school.
Is All Fish Hearing Created Equal?
Absolutely not! A fish’s sensitivity to sound will vary from species to species. This is mainly due to, believe it or not, the proximity of the inner ear to the swim bladder. Why? Because the swim bladder has gas within it which is of a much lower density than that of water. This translates to the sound wave creating a much more pronounced vibration in the cilia within the inner ear, and hence a louder sound.
Interestingly, in the majority of freshwater fish, the swim bladder is mechanically linked to the inner ear using a series of bones improving their hearing. Whilst Clupeiform fish, such as sardines and herrings, have a pair of elongated gas ducts that extend from the swim bladder and into the skull; again improving hearing. Those fish without a swim bladder, on the other hand, are well known to be hard of hearing.
Conclusion: Can fish hear?
I don’t know about you, but I can’t help but be amazed by the complexities and workings of our aquarium companions. The very thought that they have not one, but two complex systems of hearing makes them more fascinating than I can say.
It is amazing to think of what goes on in their relatively, compared to ours, little heads, and has me wondering what we will discover about them next!