Do fish sleep

Although it may seem somewhat ambiguous at first glance to be able to answer this question, it is important to know that all living beings need some time to rest and sleep to meet their vital energy needs. In this way, like all living things, we can assume that fish sleep and replenish energy, thus guaranteeing their survival. However, is the dream of fish similar to that of other groups of higher animals? Without a doubt, this is one of the many questions that nature hides between the characteristics, similarities, and differences in its immense biodiversity. Today we will find the answer to do fish sleep?

Do fish sleep? – the answer

Although it is not so common to observe fish sleeping, compared to other groups of animals such as birds and mammals, various scientific studies affirm that both fish do sleep, both bone and cartilaginous as well as agnate.

However, it is difficult to establish that fish sleep following the same criteria and behavioral guidelines that characterize mammal sleep, for example. It is not common for fish to maintain a fixed posture while sleeping, to have a quick response upon waking, or to be easily able to become active again if disturbed.

In the next sections of this article, we will discover how fish sleep exactly, what behavior patterns characterize them, as well as some curiosities about the rest of sharks, one of the most curious fish there is.

How fish sleep

There are different techniques that fish use to sleep, so establishing a single method of rest within the world of fish would be quite wrong. Let’s get to know some of these more used techniques more closely and we will better understand how fish sleep :

• Many species of fish rest on its rear or lower fin, which they place on the seabed as an anchor. In this way, the fish can sleep and ensure that they will not be washed away by possible high-pressure and high-pressure marine currents.
• As many species of fish choose to rest directly on the seabed (or freshwater, depending on the habitat they are in). In these cases, they must make use of one of their most useful internal organs, the swim bladder. Thanks to it, the fish are able to rise to the surface at times when they need oxygen from the air to cover their respiratory needs and return again to the sea/freshwater bottom without even waking up.
• Those fish that lack a swim bladder and, therefore, cannot use the prior art to come to the surface to breathe at the same time as they sleep, must remain in constant motion, being able to turn to sleep. This is the incredible and surprising case of sharks, which we will see in more detail in the next section.

Do sharks sleep?

Did you know that sharks never stop? Not even to rest, although they do not, therefore, refuse to fulfill their needs for rest and sleep. So how do sharks sleep?

As we have previously commented, fish that lack a swim bladder are those that are characterized by sleeping without remaining immobile, including sharks. These are perhaps best known for their habit of sleeping while in constant movement, since if they were not, they would risk falling to the seafloor and could die.

In this way, sharks are able to meet their respiratory and rest needs at the same time thanks to the action of the gills. The gills are external organs located on both sides of the body (between the head and the swim fin), allow sharks and other fish without a swim bladder to capture the oxygen dissolved in the water and incorporate it into their body through the respiratory system. In this oxygen uptake, it is important and vital that the animal is moving since the simple movement of water facilitates the correct diffusion of oxygen through the gill lamellae. Without a doubt, it is one of the most fascinating events that guarantees the survival of fish.

Do fish sleep with light?

Although they do not have eyelids and their eyes do not remain moist like that of other groups of animals, the fish have a protective membrane that allows them to sleep and rest, even when the sun’s rays hit them.

Therefore, we can affirm that fish can sleep with light, both in the presence of natural sunlight and artificial light that they have near fish tanks, aquariums or other habitats in which humans maintain them.

In addition, there are many natural habitats in which the depth at which fish live is not very high and therefore they sometimes receive natural or artificial light even at night. In this way, the protective membrane of the eyes that acts as an eyelid in fish will prevent them from being disturbed by any type of light while they sleep and recharge.

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