If we have an aquarium, then most often we watch the fish when we are awake: in the morning, in the afternoon and in the evening. And we don’t always think about what our pets are doing at night. But after all, all living creatures need rest and sleep, which means that it is also necessary for fish. But how do you know that a fish is sleeping, because its eyes are constantly open? Let’s try to understand this question.
What is a "fish" dream
Generally, speaking of sleep, one usually means the natural physiological state of the organism, when its response to the surrounding world is reduced, and the level of brain activity is minimal.
This happens in humans, mammals, birds, some insects and fish. On average, people spend a third of their lives in a dream (with a duration of sleep eight hours a day). In these time intervals, a decrease in heart rate and respiration occurs, the muscles relax. Such a state can be considered a period of inactivity.
But the fish are very different from the rest in biological functions of the body. Consequently, the dream they have is not quite familiar to us way.
- The environment in which they live, as well as the features of the external and internal structures do not allow them to completely disconnect from the surrounding reality.
- They do not have an absolute unconscious state, and they do not cease to fully understand the world around them.
- Their brain activity remains almost unchanged.
The sleep time of these underwater inhabitants depends on the type of fish. Those that are active during the day rest at night and vice versa. For example, a catfish hides all the bright time in a secluded place, practically does not move, and only at nightfall does it begin to swim and look for food.
What do the fish look like in a dream
Getting into the embrace of morpheus, the fish do not close their eyes. After all, they have no eyelids, and water constantly cleans their eye surface. However, the absence of eyelids does not interfere at all, since at night it is quite dark, and those fish that sleep during the day, specially swim to cover or shade the plants.
Fish that sleep can simply lie on the water, during which their gills will wash. Some can cling to the branches and leaves of plants. Other belly or side lay down on the bottom. Still others hang in the water column. In an aquarium, the sleeping fish most often drift at the bottom of the aquarium, making almost no movements, sometimes they can barely see the swaying tail. But with any, even the smallest effects of external factors (be it a danger or potential prey), they instantly revive and return to their normal state.
Briefly hibernation in winter and summer
Some species of fish at the onset of the cold season fall into the so-called hibernation. These periods, of course, differ from what we are accustomed to understand under the dream. But, nevertheless, it is also a sleep cycle.
During it, the metabolic processes in the body also decrease, all physical functions slow down, and the fish is inactive. At this time, she either hides in the shelter, or remains at the bottom of the reservoir.
And there are those fish who prefer to sleep during periods of heat. So they are protected from dehydration. The phenomenon of summer hibernation plays a very important role, as it helps the fish to survive outside of the water during dry periods or when the temperature is too high.
For example, in Africa, there is fish that turns into mud, thus creating a cocoon, and in a state of complete rest is there up to several months, until habitat conditions become suitable again. It is worth noting that aquarium fish rarely resort to such methods.
A couple of interesting facts about the dream of "wild" fish
In nature, these underwater inhabitants slumber differently:
- lying belly or sideways on the bottom, like cod;
- or up belly and upside down in the water, like a herring;
- or buried in the sand, like a flounder; or wrapped in mucus like a blanket, like a parrot fish.
The hardest thing to sleep is cartilaginous fish, especially sharks.
- They do not have a swim bladder, therefore, they cannot hang in the water, as they immediately sink to the bottom without movement.
- And they cannot lie on the bottom either, since they have not gills, but gill slits, in which water will not get into without movement, and the fish will simply suffocate.
What to do? Here’s what:
- some sharks adapted to sleep in places with a bottom current, constantly opening and closing their mouths for the movement of water around the gill slits;
- other species have sprinklers for this purpose (special gill openings located behind the eyes);
- and still others do sleep on the go. Their brain rests at this time, and the spinal cord regulates the swimming muscles.