The most surprising fact about fishes is that you cannot hear them but, they can certainly hear you. Fishes are very well-equipped for hearing. They have a pair of ears. These ears do not have an outer projection as we have, but are simply tiny holes on either side of the head, leading to the inner ear. Since there is no external ear to direct the sound, these ears are probably not as effective as our own. But the fishes have other ways of picking up sounds of vibrations in the water.
Along each side of the fish’s body is a line of little holes or pores, which can also pick up vibrations and changes in pressure inside water and pass on the message to the brain. This line of pores is called the lateral line, and can be seen quite easily.
By using this lateral line a fish can avoid all obstacles when it is extremely sensitive to pressure changes caused by the vibrations of another fish or some other objects. A fish’s lateral line contains sensory cells which provide the fish with all the information of events going on around it.
Some other teleost fishes such as catfish that lives in rather muddy water have barbells — long sensitive feelers on their mouths.
The fishes of the ‘carp’ family have tiny bones in the head which are linked to the swim bladder. The swim bladder keeps the fish upright in water and also acts as a sounding board which can pick up and magnify the tiniest vibrations, and then pass them along the bones directly to the inner ear.
These are the different mechanisms in the fishes by which they can even hear very feeble sounds.