To answer the question "How do fish sleep?"It is necessary to understand the peculiarities of their anatomical structure.
When you watch the fish in the aquarium, the impression is created, that they never rest, for their eyes are always open, but, this statement is not true. This is happening, because fish do not have eyelids on their own. The eyelid is an auxiliary organ of the eye, whose main function is to protect against external influences and drying. The latter is not scary for fish in water.
However, the fish are still asleep, although this differs from our understanding of deep and carefree sleep. Unfortunately, the peculiarities of the structure of their body, as well as habitat, prevent fish from falling into a deep sleep, during which they would be completely disconnected from reality.
What is the difference between the sleep of fish?
It is best to mark this condition with a period of low activity. In this position, the fish do not move, although they continue to perceive all sounds and are ready to take active action at any moment. Unlike most mammals, the brain activity of fish during rest remains unchanged. That's why they don't sleep like that at all, like other animals, they always arrive in a conscious state.
So what are they still sleeping fish? If you carefully observe them in the aquarium, then you can see, that periodically the fish freeze in the water without movement. The fish in this state can be called sleeping.
Depending on the species, each fish has a certain time to sleep. For an hour, in which the fish is resting, affects the environment and living conditions, as well as diet. Example, such factors may be the transparency of the water, its viscosity and density, depth of stay, flow velocity. Classifying fish by time of day for rest can be distinguished:
- day fish - light-loving. It does not mean, that at night they want to sleep, this indicates, that the structure of their eyes allows them to see better in the water during the day, and in the dark - they rest if possible;
- nocturnal fish - twilight. These fish see well in the dark, however, their eyes can be very sensitive to daylight, so during the day they try to rest. Many species of predators are nocturnal fish.
Because fish sleep, you can determine which class they belong to.
How fish sleep, belonging to the bone class?
Bone-class fish rest in calm and quiet places. They can be in sleep in various interesting poses. example:
- cod is located sideways or belly on the bottom;
- herring hangs upside down or upside down in the water;
- flounder, preparing for vacation, buried in the sand.
Before slowing down your activity, fish not only choose a pose for rest, but also try to take care of their safety. Example, parrot fish, who lives in the tropics, surrounds itself with a cloud of mucus, so that the predator could not smell it.
How fish sleep, belonging to the cartilaginous class?
Finding a favorable sleeping position for cartilaginous fish is a little harder, than bony. These difficulties are also due to differences in the structure of their body. Consider them in detail.
Bone fish, unlike cartilaginous, have a swimming bubble. The swimming bladder is a growth of the esophagus, in simple words - a bag, filled with air. Its main function is to help the fish stay at a certain depth. In order to descend to the bottom of the fish blows part of the air, and if you come to the surface - gaining. Fish, by means of a bubble simply "hang" in water on necessary depth. Cartilaginous fish do not have this ability, so they need to be constantly on the move. If it stops, then immediately sinks and falls to the bottom.
However, at the bottom of the cartilaginous class of fish can not afford to rest in peace. All the fault of the structure of their gills. Gill covers are developed only in the class of bony fish. Example, in cartilaginous sharks instead of gills just slits. Accordingly, the shark can not move its gills. In order for water to get into the gill slits, saturated with necessary oxygen, sharks need to be constantly moving, otherwise she may suffocate.
Cartilaginous fish solve this problem in several ways.
way 1
The fish are resting, located at the bottom in places of natural flow, so that water gets into the gill slits. Even in such cases, they can constantly open and close their mouths, creating a circulation of water around the gills.
way 2
Some representatives of bony fish have splashes - small holes, which are located behind the eyes. The main function of the spray is to draw water and supply it to the gills. Example, reef and tiger sharks have such a feature.
way 3
There are fish, resting in motion. Example, the inhabitant of the Black Sea never stops tar. The spinal cord of this shark is responsible for the work of the swimming muscles, so, when the brain is at rest, the tar continues to move.