Do Fish Need Sleep? Common Questions About Fish


Out of all the unique pets out there that you can own, there are none that are quite as mystifying as the fish. While the fish might be a simple creature on the outside, they are wonderfully complex little creatures. When you first get a fish, you might come to realize that there are questions that you might not ever have thought of before, until you have a group of fish hanging out in your room. For instance, most people don’t really think about how fish might communicate with each other, or if they communicate at all. A lot of people don’t know how to tell how old a fish is. Understanding how fish live out their little lives is important if you want to start caring for an aquarium of fish. Learning about this starts out with the most common question that non-fish owners and fish owners alike have: do fish sleep?

Do Fish Need Sleep?

One of the most commonly asked questions about fish is whether or not they sleep at all, and if they do, what does it look like. In fact, this question is so commonly asked, that there are research experts around the world studying how fish sleep works. The area is not well understood yet, meaning that there are a lot of assumptions made. However, there are some speculations available.

It is known that fish, as with any other creature, do need periods of resting. It has been documented that many different kinds of fish change their activity levels to achieve that period of resting. However, the nature of this supposed sleep is not nearly the same as the way land mammals sleep, which is why so many people wonder if fish actually do sleep or not. After all, fish don’t close their eyes. On a more scientific level, fish do not experience REM and they continue moving enough to float in place and breathe with their gills. In humans and other animals, REM sleep is one of the most important components of sleep, being the time when the body restores itself so it can feel refreshed. Most people also do not move in their sleep, aside from breathing. Despite all of this, it has been shown that fish do have a designated down period that could qualify as sleep for them.

What research has shown is that fish will have periods of time where they reduce their activity and their metabolism while still keeping themselves alert enough to run away from danger. Fish do this in different ways, with some fish choosing to just float in place in the middle of the water, while others might choose to secure themselves in a safe area where the danger cannot get to them. There are even some fish that find a nest-like location to do this resting. Research experts believe that these periods of resting might perform the same type of restoration that sleep provides in people, even though the fish still remains alert toward danger.

How Can You Tell a Fish’s Age?

Unlike most animals, once fish exit the egg and reach their full size, you can’t really get an idea of how old they are. With most pets, you can. For example, when dogs become older, they become stiffer, their fur becomes white or grey, and their limbs often become shakier. In fish, there are no limbs that can become stiff or weak. There is no fur that can change color due to age. So once you have a fish, how are you supposed to tell how old it is besides keeping track of the day you adopted the fish?

There are actually ways to tell how old a fish is without just memorizing the day the fish was born. With most fish, you can actually use the scales of the fish to determine the age. Removing the scale is a process in it of itself that you might not want to do, but it is possible. Typically, if you plan on doing this, you take a blunt knife and remove about 10 scales. Multiple scales are removed, as some fish develop replacement scales that will not accurately depict the age of the fish.

Once the scales have been collected, it is important to store the scales in a quality envelope so that the patterns are not damaged. When it is time to determine the age of the fish, you will want to find something that can see the finest details of the scale. One of the most commonly used devices is known as a microfiche reader. Before putting the scale on this device, you will want to moisten the scale slightly, place it on a 35-millimeter slide, and project the image onto a screen. From here, gauging the age of the fish is as simple as counting the rings on a tree. There will be wide growth rings that are called annuli (or annulus for a single ring).

With scaleless fish and fish with very small scales, there is another method that you can use. However, this method can really only be used when the fish is dead, as it requires removing a bone from the fish’s head, and you can’t really do this when the fish is alive. The bone you will want to remove is called an Otolith, or occasionally referred to as an “earstone.” There are three types of otolith, but they can all be used for this. The otolith method is quite similar to the scale method in the sense that there are rings to count to determine the age of the fish. The way to do this is complex and is often only done in studies, as it requires a lot of fish, killing some fish when they are young to determine details of the rings, and so on. But, in the end, it is possible to determine the age of a fish.

Do Fish Chew Their Food?

The answer to this question, unfortunately, depends on the type of fish you are talking about. Carnivorous fish and bottom-dwelling fish consume their food in different ways, as they both eat different kinds of food. Much like how herbivores and carnivores have different types of teeth that have evolved to better chew the specific foods that these animals eat, bottom-dwelling fish and carnivorous fish have developed different methods for consuming their food.

Carnivorous fish do not “chew” like people do. People chew their food to grind it down so that it can be swallowed. People chew tough meats to tear them apart and slice them so that a single bite can be taken. Fish, on the other hand, do make a chewing motion. They do this so that they can use their teeth to hold down the prey while they swallow it whole. At times, this process can cut the prey into large pieces for the fish to swallow. In a sense, these fish do not chew so much as hold their food down in place, although the argument can be made that they make a chewing motion, so they simply chew for a different purpose.

Many bottom-dwelling fish chew their food in a similar manner as people do. They have teeth that are designed to grind down shellfish, and herbivores will grind down plants much in the way that people chew their salads. The main difference in this process is that most of these bottom-dwelling fish have their teeth located in the back of their throat and not in their lips.

How Do Fish Communicate?

Fish, as with most other animals, need to communicate with each other one way or another, right? So how do they do it? Of course, different fish are going to communicate with each other in different manners, so it is difficult to provide a concise answer to this kind of question. The easiest answer is to simply say that fish do have different methods of communication. Fish communication involves a lot more than just noises, though. Fish communication involves smells, colors, motions, illumination, and even electrical impulses.

Like people, and most other animals, fish do communicate using sounds. When underwater, it is hard to hear sounds properly, so most people don’t even realize that fish are talking to each other. Fish sounds can be similar to purring or they can be more akin to popping. Fish usually use sound when birthing, breeding, and fighting other fish, although there are some fish species that use sound to find predators and prey.

Some fish use smell, although research on this is not complete and there is a lot left to learn about how and why fish do this. Some fish use their urine to send chemical signals, much like dogs do when marking their territory. Other fish use pheromones when it is time to breed, and some scientists believe that these pheromones are sometimes used for other social situations besides breeding.

Using color is one way that fish communicate that people can also see and recognize. For example, the blue-ringed octopus is a very well-known example of this. This octopus will reveal its classic blue rings when it feels threatened, and this is a form of communication using coloring. Fish use color to warn other fish to stay away, and they can also change their color to indicate that they are ready to breed.

Fish can also use movements to communicate with others. Typically, fish that use movement to communicate are fish that cannot produce sounds. This is also an area of fish communication that is not well-researched, but it is documented that there are types of fish that do this.

Illumination, scientifically known as bioluminescence is used in much deeper parts of the water where fish might have a hard time seeing each other. Bioluminescence is when a fish uses chemical reactions within the body to light itself up so that it is more visible. Fish do this to recognize each other and to show themselves to other creatures that might not be able to see them. This can be a warning sign or it can be a sign of recognition. Some fish do this to also lure prey in to capture them.

Finally, there are electrical impulses. These are almost exclusively done to protect the fish emitting the impulse and are used to ward off predators and threats. The most well-known example of this is the electric eel, which is an eel that is famous for shocking people (and predators) that try to go near it.