Video: Influence Of Various Conditions On The Occurrence Of Diseases In Fish
2024 Author: Molly Page | [email protected]. Last modified: 2023-12-17 15:30
Water, together with the soil of the pond bed, bacteria, algae, emerging and underwater higher plants, invertebrate forage animals, is the external environment for fish. It affects all life processes, the origin in the fish organism: respiration, nutrition, hematopoiesis and blood circulation, nervous activity, reproduction, growth and development. Therefore, for the normal life of fish and their maintenance at the proper level of vitality, it is necessary to create optimal zoohygienic conditions in ponds.
Among the variety of environmental factors that play an important role in the life of fish, the most important are the thermal, gas and salt regimes of water. By changing these factors, it is possible to regulate the environmental conditions in the desired direction and thereby prevent infectious diseases of fish.
Effect of water temperature on fish. Not only the growth and development of fish depends on the temperature of the water, but also the nature of the manifestation and course of various diseases. At the same time, both the lowest (0.1-0.2 ° C) and excessively high (above 30 ° C) water temperature have a negative effect on carp. For other fish species, these values can be shifted to one side or the other.
From a practical point of view, it should be well remembered that the resistance of fish and other aquatic organisms to the action of threshold temperatures depends on their adaptation to certain temperatures. For example, goldfish adapted to a temperature of 22 ° C can withstand a temperature rise only up to 28 ° C, and animals living at a temperature of 36.5 ° C can withstand an increase in water temperature even up to 42 ° C. Conversely, goldfish adapted to 2.2 ° C can live at 0 ° C, while for individual specimens accustomed to warm water, the LD50 is within 15 ° C. Therefore, when talking about preferred and selected temperatures, they mean that at these temperatures fish usually live in natural conditions for them, and when determining the irritating, lethal temperatures for fish, the initial adaptation temperature must be taken into account.
For fish of different species and stages of their development (eggs, larvae, fry and yearlings) certain temperatures are required.
Despite the fact that the lower temperature limit of life is much wider than the upper one, hypothermia has a great effect on all life processes and can lead to the death of living organisms. It should be noted that the more complex the organism, the more sensitive it is to the effects of low temperatures.
All types of animals, as well as humans, in terms of temperature, have a so-called biological zero, that is, that maximum tolerable lower level of body temperature at which the activity of one or another organ or organism as a whole stops. Fortunately, this process is reversible.
In most animals, including fish, the effect of low temperatures causes a number of adaptive reactions that arise mainly reflexively: narrowing of peripheral vessels, slowing down of respiration (this is especially noticeable in fish), increased metabolism (without the supply of nutrients in fish in winter and - their sharp emaciation at the same time). With further exposure to cold, compensation for heat loss is violated. In fish, along with the ambient temperature, the body temperature begins to fall, the metabolic rate weakens, the peripheral vessels expand (clearly visible on the gills). In this case, the function of the midbrain of fish is inhibited (cold anesthesia), then the hypothalamus and other centers of the nervous system of the body are inhibited. Blood pressure drops, respiratory movements of the operculums become infrequent. Hypoglycemia occurs,that is, a decrease in the amount of sugar in the blood.
The central nervous system is especially sensitive to a lack of glucose, the cells of which do not have glycogen stores. As a result, the consumption of oxygen by the brain decreases sharply. With prolonged hypoglycemia, irreversible changes occur in the nerve cells. With deep and prolonged hypothermia, the intensity decreases and the nature of metabolism changes - for example, anaerobic glycolysis manifests itself, turning into autolysis, and first individual cells die, and then the whole organism.
Of course, the resistance of the fish organism to cooling depends on its state (general resistance, fatness, age, etc.). Tissue hypoxia and irreversible changes in the nervous system are considered the main reason for the death of the body from prolonged hypothermia.
A prominent Soviet ecologist, Professor NS Stroganov, believes that a living protein is the first to suffer from hypothermia. He further points out: “Fish may not eat for a long time (months), but they endure oxygen starvation for a short period of time. If the first starvation in some fish can last up to one year, then oxygen starvation lasts only a few minutes and rarely several hours."
In some cases, even in nature, when the water temperature drops below normal, there is a sharp deterioration in the condition of the fish, although the tissue fluid does not freeze if the temperature drops slowly. then the fish go to places with a higher temperature (ecological adaptability). If the temperature drops sharply (in 1-2 days), then there is a massive death of fish (Black Sea mullet, haddock, sea and river flounder, cod, herring, sprat, etc.).
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