Summer and winter freezes. Starvation - oxygen starvation of fish

We continue our traditional section Tips from experienced fishermen - when fish die:

The amount of oxygen dissolved in water is determined in mg/l, and this indicator is used to judge the fish population of a reservoir and its hydrological regime. Thus, in small fast cold rivers the upper threshold reaches 12 mg/l, in lowland rivers, large flowing lakes and reservoirs - 9-7 mg/l, in small closed lakes and ponds - 5 mg/l. In summer, during the intensive growth of algae and submerged aquatic vegetation in lowland rivers and lakes, these indicators are higher, since plants release oxygen into the water during photosynthesis. In autumn, as the water temperature drops, the amount of dissolved oxygen begins to decrease.

But as the air temperature decreases, the solubility of oxygen in water begins to increase, since the intensity of mixing of water and air also increases, which is facilitated by the powerful autumn wind-driven disturbance of river currents. With a subsequent decrease in temperature, aquatic plants and algae begin to die off, the intensity of photosynthesis is reduced to zero, and the content of dissolved oxygen in water depends only on the mechanical effect of air on water.

Next comes a critical period in the life of the fish population of the reservoir - the establishment of a dense ice cover, which almost completely blocks the access of oxygen from the air to dissolve in the upper layer of water.

Theoretically, the oxygen accumulated in water should be enough for fish, since the intensity of their metabolism, and therefore oxygen consumption, decreases several times. But, besides them, a lot of other animals winter in the reservoir: planktonic and benthic invertebrate animals, aquatic worms, leeches, insects and amphibians. In addition, during the warm period the reservoir accumulates huge amount organic matter: dead vegetation, leaves, pine needles, branches, waste residues and animal corpses, as well as “products” of human activity. This organic matter takes up a large proportion of the oxygen dissolved in the water for decomposition. This releases carbon dioxide, which at high concentrations is toxic to fish, and when decomposed incompletely, hydrogen sulfide, which causes asphyxia in fish.

The establishment of a strong ice cover and the impossibility of contact of water with air for gas exchange are the main factors that can cause death.

The most favorable in terms of death (they are practically absent) are small fast streams and rivers with a large number of springs and riffles along the watercourse bed. Water flowing through changes in the riverbed is mechanically enriched with oxygen. Such reservoirs are inhabited by fish species that are least resistant to oxygen deficiency: brook trout, European grayling and sculpin. The threshold dissolved oxygen content for such fish species is 7-5 mg/l.

Deaths in such watercourses are rare and usually occur after severe frosts, when the water on the riffles freezes, blocking the flow of oxygen-rich water to the underlying section of the channel. But such phenomena are usually short-lived and do not cause serious losses to the fish population. Small lowland rivers can be considered the next most prosperous. Their bed also has riffles and spring outlets, but the flow speed in such watercourses is lower compared to the above, and the ice cover is greater. These rivers are home to oxygen-demanding species such as chub, asp, bystryanka, barbel, gudgeon, and podust (the threshold dissolved oxygen content for such fish species is 5 mg/l). The danger can be posed by quickly starting ice drift, when large ice floes block the river bed or the outlets of oxbow lakes in several places, forming ice jams. In such areas, the oxygen content can drop to critical levels when, after a strong thaw, melt water, passing through the fields, washes fertilizers and humus into the river.

Organic matter decomposes there, causing a sharp drop in the oxygen content of the water. And since the fish’s migration routes are blocked, they can completely die in the area fenced off by ice. In addition to small rivers, this phenomenon also occurs on large lowland rivers, but there the consequences of congestion are less pronounced and short-lived. Human activity introduces additional danger.

Reservoirs are often built on small and medium-sized rivers, which act as an accumulator of organic matter. In addition, so-called “working down” is carried out at reservoirs - releasing excess water before the spring flood. This leads to the collapse of the ice shell, the release of water onto the ice, and in the event of a sharp discharge, to the blocking of the flowing river bed by ice. And if severe frosts persist during this period, then the water that comes out on the ice, flooding all the cracks, freezes, and death cannot be avoided. This usually leads to almost complete death of fish in the reservoir.

Next, we will consider deep flowing lakes with an area of ​​500 hectares or more. In our country they can be divided into two groups: located in the south, Polesie, and northern. The latter are the most prosperous, quite deep, fed by a large number of streams and rivers. Even when stable ice cover is established, the dissolved oxygen content does not fall below 7-5 mg/l. In such lakes, where vendace, whitefish, pike perch, and burbot live, there are practically no death phenomena observed.

Southern lakes are characterized by weak flow, shallow depths, and most importantly, thick deposits of sapropel and silt. In spring, summer and autumn, the content of oxygen dissolved in water due to the rapid development of plants is quite high - about 9 mg/l. But in winter, after freezing, dead plants and silt begin to take oxygen. Deaths on such lakes are not uncommon. Fish species that require little oxygen content - perch, roach, bream, pike - can live here (threshold oxygen content is 4 mg/l). Fish of these species die regularly. True, a small proportion of adult individuals still survive death.

The last group of reservoirs includes small, several hectares in area, floodplain and swampy lakes, as well as stagnant ponds. Such reservoirs are found throughout our country, but the largest number of them are concentrated in the Brest and Gomel regions. Their depth rarely exceeds 1 m, the bed is muddy and heavily overgrown.

In summer, due to the shallow depths, plants rapidly develop in them, but after freezing, all dead plant mass decomposes, taking away oxygen. The reduced oxygen content in such reservoirs in winter is an annual phenomenon, and the species composition of fish is corresponding: silver crucian carp, golden crucian carp, loach and tench, that is, the species that are most resistant to oxygen deficiency. The threshold oxygen content for these fish species is 0.4 mg/l.

Alexander ZUBEY (magazine “Hunting and Fishing”)

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The article “When fish lack oxygen, massive fish deaths, fish deaths in winter” has been published.

Zamora- one of the most terrible natural phenomena in which fish die from oxygen starvation. They can occur in both winter and summer. The most common freeze-up of a reservoir is in the winter (from January to April).

And the essence of this phenomenon is as follows. As water temperatures drop in the fall, the amount of dissolved oxygen decreases. However, the solubility of oxygen in water increases due to the active mixing of water and air due to intense wind disturbance of the water surface. With a subsequent decrease in temperature, aquatic plants and algae begin to die off, the intensity of photosynthesis decreases, and the content of dissolved oxygen in water begins to depend on the mechanical effect of air on water. This is followed by a critical period in the life of the ichthyocenosis of the reservoir - the establishment of a dense ice cover, which almost completely blocks the access of oxygen from the air to dissolve in the upper layer of water.
In winter, the intensity of physiological metabolism in fish decreases, and accordingly, their need for oxygen decreases several times. But, besides them, a lot of other animals winter in the reservoir: planktonic and benthic invertebrate animals, aquatic worms, leeches, insects and amphibians. In addition, during the warm period, a reservoir accumulates a huge amount of organic matter: dead vegetation, leaves, pine needles, branches, waste residues and animal corpses, as well as “products” of human activity. This organic matter takes up a large proportion of the oxygen dissolved in the water for decomposition. This releases carbon dioxide, which at high concentrations is toxic to fish, and when decomposed incompletely, hydrogen sulfide, which causes asphyxia in fish. In scientific language they say that the phenomenon of death is associated with excessive eutrophication of water bodies. And in winter, the establishment of a strong ice cover and the impossibility of contact of water with air are the main factors that can cause death.

The most sensitive to a lack of oxygen are roach, perch, pike, bream, and verkhovka. Salmon and sturgeon usually simply do not live in such reservoirs in the wild. But, if they were artificially released into such a reservoir, then they are the first to die. Carp are less susceptible to winter death. But crucian carp and rotan almost always survive such conditions.

In addition to winter pestilence, there is also summer pestilence. It falls during the hottest months of the year and mainly occurs in July - August. It occurs as a result of abundant blooms of algae (most often blue-green) and is dangerous because it clogs the gills of fish and reduces their filtering ability. In addition, with increasing water temperature, the solubility of oxygen in water decreases significantly. That is why during the hot summer months, at high water temperatures, the fish are depressed and prefer to feed in the dark.
Summer death most often occurs in shallow reservoirs, abundantly overgrown with aquatic vegetation.

How to deal with these natural phenomena? On at the moment There are many different ways: running oxygen under the ice helps relieve winter cold. Fishing holes do not save a reservoir from starvation; real, large mines are needed. Most in an efficient way The solution is to install aerators. They create large gullies in the ice thickness and effectively mix oxygen with water through the flow they form. There is also another method - a chemical one. The industry produces special oxygen tablets, which, when in contact with water, release a certain amount of oxygen.
Against summer death, the most commonly used method is to clear the reservoir of aquatic vegetation and the bottom of the reservoir from silting. They use special water mowers and harrow the bottom. However, you should be careful with the last procedure, since harrowing over a large area can itself provoke the death of the fish.
Methods of biological purification of a reservoir from aquatic vegetation are also used - introducing herbivorous fish such as grass carp, silver and bighead carp and their hybrids into the reservoir. However, for this measure to have a positive effect, it is recommended to carry it out only after an ichthyological examination of the reservoir and consultation with specialists.

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By its devastation fish kill is the greatest disaster. A colossal amount of commercial fish and their young die every year in many water bodies. Many good reservoirs, abundant with fish, were devastated and devalued by death. Sports centers were closed because of him. In many lakes and ponds, for the same reason, it is impossible to breed valuable species fish, and the ponds are used only for summer rearing of carp. In winter, carp that are undercaught in ponds, with rare exceptions, completely die from starvation.

Fish kill occurs from lack of oxygen in the water. In summer, oxygen enters the water from the atmosphere and is released by aquatic plants. It is continuously consumed for the oxidation (rotting) of sludge and dying aquatic animals and plants, as well as for the respiration of aquatic organisms. If a reservoir is heavily overgrown or microscopic algae develop (“water bloom”), oxygen consumption in the summer may be significantly greater than the supply, especially at night, when plants do not produce oxygen. In these cases, death can occur in the summer. But summer frost is less common. The main danger is death in winter, when the ice cover prevents the flow of oxygen into the reservoir from the atmosphere. During this period, plants do not enrich the water with oxygen. The amount of oxygen in the water can decrease so much that the fish begins to suffocate. Often the entire fish population of a reservoir dies, or many valuable fish species die and only crucian carp survives.

Unfortunately, people often look at death as an annoying, but completely natural phenomenon. They regret the death of fish and the devastation of water bodies, but they care little about the fight against death. And in some places they even try to make money by killing people.

The idea of ​​the inevitability of death was facilitated by the absence effective means of combating with this evil. In reality, starvation can and should be fought. Summer freeze-up in fish ponds is eliminated by spraying water with garden sprinklers. Until recently, as almost the only “preventive measure” against winter death, “vents” were used - large ice holes that are cleared of ice from time to time. In some cases, sheaves of straw, reeds or reeds are frozen in an ice hole, naively believing that a sufficient amount of air will pass through the sheaves into the water.

• The impression of the usefulness of ice holes is created because when fish are dying, they first desperately “climb into the ice hole,” and then their movement stops. So they think that thanks to the ice holes the fish “caught their breath.” This conviction is strengthened by the fact that often after death in a stagnant body of water in the spring and summer it is discovered live fish. In addition, the fish in the ice holes become more active and careful towards the end of the kill.

In reality termination of the "move" fish means that all or part of it is already died - "died", as the fishermen say. And indeed, in an ice hole in a stagnant reservoir, you can see a lot of dead fish lying on the bottom. In addition, part of the fish population of the reservoir stops going into the ice holes, as they find less choked zones. After all, death does not always spread throughout the entire body of water. Such favorable zones occur near springs, in places with an air gap under the ice, which, when the water level decreases, hangs on hummocks, bushes, reed thickets that have been flooded since the fall, or on the slopes of a steep bank. The survival of fish in these zones until spring reinforces the belief in the action of “breathers”.

Increased mobility and alertness fish in the ice hole after the toga, as many fish were taken from it by hand, is explained by the fact that the water in the ice hole is slightly refreshed, especially due to splashes when catching fish. In such water, the fish does not experience suffocation and becomes more mobile. However, based on the few specimens of fish staying at the ice hole at this time, it cannot be judged that all the fish in the reservoir are also feeling well. After all, the volume of refreshed water in the ice hole is very small, and in the absence of a current, already at a distance of 1-2 m from the “vent” the reservoir is frozen. That is why dead fish are visible near the ice hole.

• Water has its greatest density at +4° C. When heated and cooled, its specific gravity decreases. Cooling in the ice hole from contact with air, the water becomes lighter and, in the absence of flow, forms a kind of liquid plug. Consequently, the refreshing effect of the “air” cannot spread throughout the reservoir. In addition, ice holes freeze very quickly, and keeping them open means best case scenario, to their 2-3-fold renewal during the day.

In places with a noticeable current, water refreshed in the “vent” spreads beyond the ice hole.

8.08.11. At the end of the week, the Desna River in Novomoskovsk Troitsk was covered with dead fish like a carpet.

Officials assume that the crucian carp and grass carp suffocated due to the massive discharge of sewage, but the townspeople are confident that the situation is much more serious: the river has been polluted for many years, and this is the first time such a massive pestilence has occurred.
“We went by boat yesterday and assessed the situation. I won’t tell you the exact number of fish that surfaced, but it’s a lot, I’ve never seen anything like this,” Vasily Romanenko, head of the department for civil defense, emergency situations, environmental and territorial security, told MK.

According to the official, no one thought that there could be so many living creatures in the river: grass carp, crucian carp, carp, roach and rudd floated to the surface. The prosecutor's office, administrative technical supervision and police officers have already visited the scene of the disaster and are establishing the cause of the mass pestilence. The water analysis will not be ready until August 10, but for now inspectors are considering the possibility of a sewer break. “There is a pipe sticking out from under the ground near the shore, from which there is a constant drain, however, we do not yet know whose it is - the FSB recreation center “Moscow Evenings” or the FSB dacha cooperative “Leto,” said Vasily Romanenko.

Local residents, however, are confident that law enforcement will only write off the disaster as an unauthorized drain, and will hush up the real cause. “Back in 2010, we wrote to both Medvedev and Gromov about the terrible situation on the river, where everyone is dumping sewage, and this is a well-known fact. Sewage has been drained for years, but never have so many fish died in just a few days! This means that there was some very serious toxic release, most likely from “Moscow Evenings”. Only the head of the Admtekhnadzor is their regular, and the matter will probably be hushed up,” Igor Slepovich, editor of the Troitskie Vedomosti newspaper, told MK. According to him, 10 years ago the city had large number equipped beaches and half the city swam in the river.

Now the beaches are built up or closed, and swimming is officially prohibited. More than once, local residents turned to the administration with a request to give the Desna the status of a protected area and develop recreational areas, but since the 2000s, the river has only been filled up, for example, for a complex of 17-story buildings, which are located a few meters from the shore. Sewage from houses, according to townspeople, is dumped directly into the river. And now, in the Desna water protection zone, not far from the high-rise buildings, a gas station complex with a car wash is being built without its own treatment facilities.

True, now there is a catastrophe with the fish Russian tradition can turn the situation around. “The damage to nature has been colossal; it is not yet possible to estimate it in numbers. It is only clear that the river will have to be completely cleaned and the fish population restored. But who will do it and how, I can’t tell you right now,” Vasily Romanenko explained to MK. “In our country, for the authorities to pay attention to the problem, something terrible really has to happen: either a ship with a hundred people will sink, or the river will turn white from dead cupids,” says Igor Slepovich. Now, according to him, the dead fish from the FSB recreation center were carried away by the current: the dam's poles were opened - and the crucian carp and carp swam further down the river. The editor believes that this is for the better: downstream there is a health complex of the Presidential Administration, so the problem of river pollution will definitely not pass by the country's leadership.

Fish, like other animals, cannot live without oxygen. The enrichment of water with oxygen occurs in two ways: from the surrounding air due to wind and rain, and also due to the vital activity of green plants. As a result of a lack or complete absence If the water lacks the oxygen necessary for fish life, fish may die. If the amount of oxygen in the water decreases sharply, the fish become restless and often die.

Depending on the seasonality and time of occurrence, there are three types of fish kills: summer, night and winter.

Summer cravings observed in the hot season (June-July) with high temperatures in rivers, lakes, and reservoirs heavily overgrown with blue-green algae, giving the water a dense green color. The more silted a water body is, the more vegetation there is and the worse it is for fish. In addition, as a result of flooding of floodplain sections of rivers caused by heavy rains or floods, fish kills may occur in the summer caused by rotting of the flooded vegetation.

Of particular danger is the entry of swamp and industrial wastewater into the reservoir, which leads to massive death of fish. The waters entering fishing grounds from swampy areas contain large amounts of organic matter and are poor in dissolved oxygen.

Night freezes are a type of summer kills and are observed in shallow water bodies, heavily overgrown various types aquatic vegetation. As a rule, such freezes are observed in the morning and quickly pass with the advent of light.

Lack of oxygen in the water causes anxiety in fish. The fish begin to move, and therefore their need for oxygen increases. With a lack of oxygen in the water, fish experience: pallor of the gills and mucous membranes of the mouth (sometimes with a pronounced bluish and dirty bluish color); eyes become cloudy; rapid breathing - fish breathe with an open mouth and gills.

Winter freezes are observed both as a result of a complete cessation of oxygen supply from the air and a sharp limitation of the life activity of plants under the ice. The establishment of a strong ice cover and the impossibility of water contact with air (gas exchange) is the main factor that can cause death. Winter frost does not occur everywhere within the boundaries of each individual reservoir, but in separate areas, the areas of which change from year to year. Very often, especially in winter, you can see how fish accumulate in the ice holes, greedily gasping for air. Harbingers of death are swimming beetles and other insects that gather in ice holes.

Measures to prevent fish kills.

To prevent the occurrence of death in the summer season, it is necessary in every possible way to prevent excessive overgrowing of water bodies with hard surface vegetation. The more common plants that need to be dealt with include: reeds, reeds, sedges, cattails, calamus, etc. Tough vegetation is destroyed by mowing, which is carried out during the flowering period of the plants, since during this period they have the smallest supply of nutrients and can no longer will be able to give rise to new shoots in the future. Mown tough vegetation should be removed in a timely manner. It is also important to clear channels and springs, mow down vegetation in floodplains, reclamation canals and others.

To prevent the occurrence of winter fish kills, it is necessary to organize operational control over the content of oxygen dissolved in water during the period after the formation of ice and before its disintegration in the reservoir (January-March). When the oxygen concentration decreases, it is recommended to arrange ice holes (2 x 2 m, 1 piece per 3-5 hectares), and clear the ice field of snow (up to 30% of the area). Amateur fishermen who visit water bodies can help wintering fish: several holes cut are an additional amount of oxygen in the water.

An effective measure to prevent fish kills in reservoirs and watercourses prone to kills is the addition of lime. Liming promotes the decomposition and acceleration of mineralization of organic matter, as well as improving the gas regime, neutralizing the acidic reaction of water.