About Fish And Their Hearing

Anyone who has pet fish wonders if they can hear tapping on the tank, or sounds outside the tank. Fish don’t have ears like we do, so can fish hear?

Yes, fish can hear, although not quite in the same way we do.

How Do Fish Hear?

Exactly how a fish hears depends on the species. Some species live in large groups and can rely on the school’s hearing as a whole. Others live almost entirely alone, and would need a more developed sense of hearing. Deep water fish would need a different sense of hearing to fish who prefer the shallows. Meat eating fish would need to hear prey fish to be able to hunt effectively, whereas herbivorous fish wouldn’t need the same heightened hearing senses. 

Most fish hear through the otoliths which is an ear of sorts, or the lateral line. Some species can also hear through their swim bladder. 

Otoliths

The otolith is a calcium carbonate structure in the inner ear. Fish ears start with a tympanum, a membrane that acts a lot like a drum cover. Beyond the tympanum, are three otoliths, which have a similar function to the three bones in our own ears. 

Otoliths are behind the fish’s brain, inside a fluid chamber. There is a larger otolith, called a sagittae, and two smaller otoliths, called the lapilli and the asteriscii. The larger otoliths, the sagittae, are more commonly studied, but this is entirely because the size means that they’re easier to work with. 

Otoliths grow as the fish grows, creating new layers of calcium. A fish can be aged by counting the rings of a cross section of otolith. Interestingly, otoliths are different sizes and shapes, depending on the species of fish. 

Scientists and marine biologists don’t only look at otoliths to age the fish. These ingenius little structures can convey so much more information as well. They’re actually a pretty good window into the fish’s life. 

For example, a darker ring in the otolith would suggest that the water temperature dropped, or that the fish found himself in cooler waters. Lighter colored rings would show that the temperature was unusually high, or the fish was in warmer waters. Thin rings would show that food was scarce, and the fish didn’t grow very much for a period of time, or thicker rings could show that there was an abundance of food. 

The otoliths detect the vibration of sound, and translate it to the brain in a way that it can understand. They also help detect motion, pinpoint direction, and maintain balance. This is probably why flying fish have more developed otoliths. 

Lateral Line

The lateral line is also known as the lateral line organ, or the lateral line system. You can see it if you look closely at many fish species as it many be a slightly darker color than the rest of their scales. 

The lateral line works by allowing fish to sense changes and vibrations in the water. It’s actually very important for feeding and schooling behavior. Studies have found than blind fish are able to make their way back to their school, however, fish who have a damaged or impaired lateral line are unable to do so. 

The lateral line works by using an organ called a neuromast. This organ is what fish use to sense changes in the water. There are two types of neuromast. 

A superficial neuromast is on the outside of the body. A canal neuromast is in the sub-dermal layer of the lateral line. 

The neuromasts are made from receptive hair cells. These hair cell tips are covered with a flexible jelly type covering. The hair cells are similar to epithelial cells, although there are some differences. The cells have bundles of microvilli hairs, which are the mechanism that senses vibrations, and mechanical changes of the water. They aren’t all the same length, and the varying lengths creates a sort of stair case. 

The lateral line is also able to detect the direction a sound or movement is coming from. The fish can judge the direction and distance of the sound or movement by how the hair cells move and the force that makes the hair cells move. 

Both types of neuromast can do this, but superficial neuromasts are better designed for a wide range of detection. Canal neuromasts are designed to pinpoint the cause of the sound or movement with better accuracy. 

The hair cells are similar to, and interact with the hair cells in a fish’s auditory system, which is how the lateral line helps a fish hear. 

Swim Bladder

The main function of the swim bladder is to keep the fish buoyant, however in some species, it acts as a hearing tool as well. In some species of cichlids for example, the swim bladder takes on a second function as an ear drum. 

It detects sound and movement, and transmits this information to the inner ear for auditory processing. These species have slightly different swim bladders to other species, in that they’re more specialized. These species can detect both higher frequency sounds, and lower frequency sounds better than species without a specialized swim bladder. 

Studies also suggest that size plays an important role in this method of sound detection. In essence, research seems to show that the bigger the swim bladder, the better the hearing, though research is ongoing. 

Can Fish Be Trained To Voice Command?

Some fish can be trained to recognize voice commands. Betta fish, for example are considered to be among the most intelligent fish species, and can recognize voices outside the tank. 

Research suggests that it’s unlikely that they can distinguish your voice from someone else’s. However, they can be trained to perform some basic tricks by voice command. 

Coming By Name

Fish won’t recognize their names in the same way as a dog does, or as a cat does (when it wants to). They can, however, be trained to come to the surface for food, which means that they will associate the sound of the name with getting food. Any time you say the name, the fish is likely to come to the water’s surface looking for food. 

Teaching Your Betta Fish Tricks

Before you start teaching your fish tricks, you need to prepare him, and yourself. 

  1. Getting Familiar With Your Fish

Betta fish don’t have a fantastic sense of sight but this doesn’t mean that they can’t learn to recognize your face. The best way to do this is to spend time near the aquarium, letting them see you. As they become more familiar with you, they will start to come towards you whenever they see you. 

  1. Give Them Treats

As we’ve said, fish won’t come to the surface of the water because you said his name, but because he’s coming for food. He will learn to associate the word you use as his name with eating. This can be used to train him with treats, in the same way as a cat or a dog can be treat trained. You can use brine shrimp, bloodworms, daphnia, tubiflex worms, or mosquito larvae. 

You need to take care not to feed too many treats, as overfeeding can become a problem. Also if you feed frozen treats, make sure that you thaw them first. 

  1. Health Matters

Happy, healthy fish will respond better to training, so make sure that the aquarium is set up properly. You fish needs to be active, swimming normally, and in a habitat that closely replicates their natural environment. 

  1. Wash Your Hands

Before you start closely interacting with your fish, you’ll need to wash your hands in hot water. You shouldn’t use soap, only use hot water, as most soaps are actually toxic for fish. 

Tricks To Teach

The following are some basic tricks for your fish to learn. Remember training takes time and patience, with a lot of repetition. 

  • Follow – You can teach your fish to follow your finger along the tank. Make sure you have his attention and drag your finger along the side of the tank. When he does this, give him a treat as soon as possible. You can use a training word, such as follow for this as well, so that when he knows the trick, he will eventually swim the line when he hears the word. 
  • Flare – Betta fish flare their long fins when they need to show aggression, so the easiest way to teach this trick is to say ‘flare’ and use a mirror to show your fish his reflection. Back this up with a pen, but make sure you use the same pen every time you train, and reward him with a treat as soon as possible. 
  • Jump – Jumping is a natural behavior for Betta, so teaching him to jump on command can be great fun. You’ll need a feed stick, so you can start by feeding him a treat under water. As he gets used to eating from the stick, you can move it slightly further away from him until you have the stick outside the water. You can add the word ‘jump’ so he can learn to do this trick by voice command only.