In science, there is a definition of the concept of atmospheric pressure – this is the force of the impact of the air 1 cm of the surface. That is, the planet is surrounded by an air mass, 
which under the influence of gravity is pressing on any object, including the human body, and the bodies of all living creatures. This force is called the pressure of the atmosphere. Measurement of atmospheric pressure is made by a special instrument – a barometer. Barometer readings help to accurately find out the current indicator of atmospheric pressure, as well as to predict the possible weather changes.
The States of Atmospheric Pressure You Should Know About
As is known, atmospheric pressure is constantly changing. Its cyclic changes are associated with daily, annual, seasonal and other cycles in natural meteorological processes. Noncyclic changes are observed in the formation and destruction of cyclones and anticyclones.
Low Atmospheric Pressure
Lowering of the atmospheric pressure is not common, but under certain conditions, it can lead to very serious consequences, called “altitude sickness”, which is based on oxygen starvation of tissues, in which the level of carbon dioxide begins to increase catastrophically. Vessels of all organs (with the exception of the heart and brain) react to 
hypercapnia (increased concentration of carbon monoxide) by spasm, significantly increasing the pressure in a large circle of blood circulation.
This situation is typical for farm animals that live in mountainous areas. In order to prevent critically poor animal health, they move to higher pastures and back at a slow pace. So they manage to adapt.
High Atmospheric Pressure
The increase in atmospheric pressure per se is not dangerous for the organism and, if certain safety rules are followed, does not cause even discomfort, and all processes are reduced to the accumulation of air gases (mainly nitrogen) in tissues and blood (the so-called compression stage).
How Pressure and Weather Affect Animals
Atmospheric pressure significantly affects the climate, and its fluctuations cause a significant change in the weather. At high atmospheric pressure, there is usually good weather – cloudless sky, dry air and lack of strong wind. Low pressure, on the contrary, is 
accompanied by cloudiness, precipitation, fog formation, and therefore adversely affects animals.
Frequent changes in weather have a negative effect on the health and productivity of animals. Raw, cold weather contributes to the occurrence of colds, hot weather leads to gastrointestinal, invasive and infectious diseases.
The Role of Atmospheric Pressure in Animal Life
The direct effect of atmospheric pressure on living organisms has so far been poorly studied, although there is no doubt that it is significant. This is because, firstly, living organisms are always forced to equalize the internal hydrostatic pressure with the external atmospheric pressure.
Using the example of a human, one can see that in the event of a failure in the physiological mechanisms responsible for this process, fairly widespread pathological conditions arise, such as hypertension (high blood pressure) and hypotension (low). On the other hand, the absolute amount of oxygen contained in the same volume of air depends 
on atmospheric pressure. The combination of these two actions of atmospheric pressure lies, in particular, in the basis of the so-called mountain sickness, which develops when people without preparation get from a lowland area low above sea level to high altitude conditions, where the atmosphere with rising up is more and more rarefied. Naturally, living organisms can respond to long-term changes in atmospheric pressure by adaptive physiological changes in the body. The results of studies of organisms adaptations to living in the mountains speak directly about this.
Thus, atmospheric pressure has a significant impact on animals and birds. When the conditions change, the body reacts, which leads to a decrease in potential productivity and product quality (this is relevant for farm animals).
Fish Behavior: The Most Revealing Example
The atmospheric pressure affects primarily the change in the density of water. With increasing pressure, the density of water rises, and its level becomes slightly less. When the pressure is lowered, the picture is reversed. In both cases, the fish are forced to find that level of water (depth) on which they will feel comfortable. In this case, the fish undergoes a short period of adaptation, during which it stops eating. Large fish specimens 
react to changes in atmospheric pressure most painfully.
It happens that for several days, the pressure jumps abruptly. In such periods the fish does not have time to adapt to constantly changing conditions, and is forced to refuse to search for food. Accordingly, it does not make sense to go fishing at this moment.
Atmospheric pressure acquires the greatest value in the life of fish in winter. Cold water in winter acquires the greatest density. The fish require a lot of energy to overcome the resistance of “dense” water. High atmospheric pressure only aggravates the situation. A smooth decrease in pressure always leads to increased activity and biting. This period continues until another anticyclone coming.
