Although at first glance being able to answer this question seems somewhat ambiguous, it is important to know that all living beings need some time of rest and sleep to meet their vital energy needs. In this way, like all living beings, we can assume that fish sleep and replenish energy, thus guaranteeing their survival. Nevertheless, the dream of the fish is it 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 of its immense biodiversity.
Continue reading this Green Ecologist article in which we answer in detail the question of: 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 the bone and the cartilaginous as the agnate.
However, it is difficult to establish that fish sleep following the same criteria and behavior patterns that characterize sleep in mammals, for example. It is not common for fish to maintain a fixed posture while sleeping, to have a quick response upon awakening, or to easily count on being 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, some of the most curious fish there is.
How fish sleep
There are different techniques that fish use to sleep, so to establish a single method of rest within the world of fish would be quite wrong. Let's get to know some of these most used techniques more closely and we will better understand how fish sleep:
- Many species of fish rest on its hind 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 swept away by possible ocean currents of great force and pressure.
- As many species of fish choose rest directly on the bottom marine (or freshwater, depending on the habitat in which they are found). 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 on occasions when they need oxygen from the air to meet their respiratory needs, and return again to the seabed / freshwater without even waking up.
- Those fish that lack a swim bladder and, therefore, cannot use the prior art to surface to breathe while sleeping, must stay in constant motion, in turn being able 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 sharks never stop? Not even to rest, although this does not mean they refuse to fulfill their rest and sleep needs. So how do sharks sleep?
As we have commented previously, fish that lack a swim bladder are those that are characterized by sleeping without remaining immobile, among them, sharks. These are perhaps best known for their habit of sleeping while in constant motion, since if it were not like that, they would run the risk of falling to the seabed and could die.
In this way, sharks are able to cover both their respiratory and resting needs thanks to the action of their gills. Gills They are external organs located on both sides of the body (between the head and the swim fin), they allow sharks and other fish without a swim bladder, to capture the dissolved oxygen 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 the 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.
Learn more about this question in this other post: Do sharks sleep?
Do fish sleep with light?
Even if lack eyelids and their eyes do not remain moist like those of other groups of animals, fish have a protective membrane that allows them to sleep and rest, even when the sun's rays reach them.
Therefore, we can affirm that fish can sleep with light, both with the presence of natural sunlight and with 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 the 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 which acts as an eyelid in fish, will prevent them from being disturbed by any type of light while they sleep and replenish energy.
To finish, we encourage you to watch this curious video about animals that sleep strangely, because fish are not the only ones that rest in ways different from ours.
If you want to read more articles similar to Do fish sleep?, we recommend that you enter our category of Animal Curiosities.
Bibliography- Drafting Team. How much do you know about sharks? National Geographic Spain: Nature.
- Del Río-Bermúdez, C. & Karlsson, K. (2013) The zebrafish (Danio rerio) as a dream animal model: swimming in a new direction. Science Cognitive, University of Granada (Spain), Volume 7 (1), pp: 1-4.
- Lagler, K., Bardach, J., Miller, R. & Passino, D. (1984) Ichthyology. AGT EDITOR, S.A., pp: 305-373.
- Hendricks, J., Sehgal, A. & Pack, A. (2000). The need for a simple model to understand sleep. Progress in Neurobiology, Volume 61, pages 339-351.
