Fish is a temperature-changing animal that lives in water. Changes in water temperature are closely related to the growth of fish. As the winter falls, the water temperature drops, and the fish will enter the wintering state. From mid-October onwards, the water temperature dropped to about 10°C, and fish basically stopped feeding. By the beginning of April, the thawing occurred in early April. This period of time during which the fish started eating was called the wintering period.
During the winter of fish, dead fish occurs in the fish pond every year, but only at different levels. Therefore, in order to improve the survival rate of fishes in winter, the author studied the physicochemical and biological conditions of wintering waters of fish and the physiological changes of fishes during wintering, as well as the precautions for wintering in ponds and the management methods for overwintering. . This article will introduce the environmental conditions and technical characteristics of fish overwintering.
First, the basic conditions for wintering pool should have
1. The water depth should ensure that the wintering pool is not more than 1.5 meters above sea level. As the wintering pool is in the long-term freezing period, the pool water continuously leaks. Therefore, it is not enough to consider only the depth of water when entering the pond. Pay attention to changes in the water level in the wintering pond and take timely measures to make the wintering pond water within the required range. .
2. The bottom of the bottom pool should be flat, and the thickness of the sludge should be about 10cm. Because the sludge contains a large amount of humus, although it can play the role of fertilizer supply, fertilizer maintenance, and water quality regulation, excessive sludge will be decomposed during the process. Consuming large amounts of oxygen is prone to hypoxia. Therefore, the sediment in the wintering pond should be removed as much as possible.
3. Water quality Fish should not use old pond water for wintering, and it is better to blend in more than half of the new water. The transparency of the water should be greater than 35 cm. Keeping a certain amount of phytoplankton in the water, using photosynthesis under the ice and supplementing the oxygen in the water, can play a role in improving water quality.
4. Water source wintering ponds are preferably near the water source or use the surrounding fish ponds to store water to make up for the wintering pond if necessary. The water quality of the water source must meet the water standard for fish farming. If groundwater such as well water is used, it is necessary to try to increase the oxygen content and to increase its oxygen content and discharge harmful gases such as toxic hydrogen sulfide to ensure the safety of fish wintering.
There is no special requirement for the area of ​​the wintering pond, as long as the pool is convenient, the size can be, the best area is 10 acres to 20 acres.
Second, the main physical and chemical factors of winter water body changes
1. Water temperature ice overwintering pool ice water temperature often occurs vertical stratification phenomenon, near the ice water temperature is generally around 0 °C, down gradually increased, such as the depth of 1.5 meters above the water level of the bottom up to 4 °C. Winter fish are generally clustered in deep water. The vertical distribution of water temperature in wintering ponds is shown in Table 1.
If oxygenation measures such as circulating water or replenishing water are used, the natural vertical distribution of water temperature under ice will be broken down, and the water temperature at the bottom can be reduced to 0.2°C. When the water injection is stopped, the water temperature will naturally rise but the water temperature at the bottom will generally not reach 4 °C.
2. Illumination under the ice In addition to the thickness of snow on ice more than 50 cm, the water layer under the ice can have a certain amount of light. The degree of illuminance is closely related to the transparency of ice and the thickness of snow, but less to the thickness of ice. Bright ice, regardless of thickness, light transmittance of up to 30% or more, up to 63%. The ice transmittance is generally about 10% and the maximum is 12%. Snow cover 20 cm to 30 cm, the light transmittance is greatly reduced, only 0.15%. Binzhou, Shandong Province is not very cold in winter and its ice thickness is about 40 cm to 45 cm. It sometimes melts at noon and then freezes again. This ice ice has poor light transmission. Although the ice is not thick, the light transmittance under the ice is very high. reduce. If the snow can be cleaned in time during winter, maintaining a high light transmittance, the underwater illumination can basically meet the needs of algae photosynthesis. This is very beneficial to improving the quality of overwintering water and increasing the dissolved oxygen content.
3. Water quality The stocking density of the fish wintering pond is higher than that of the rearing pond. After the pool is frozen, the water is isolated from the air, creating a small environment that is not affected by the atmosphere. Therefore, the metabolic activities of fish and aquatic organisms and the decomposition of organic matter are all carried out in this small environment. Therefore, the consumption of oxygen and the generation of metabolic wastes will cause great changes in the physicochemical and biological conditions of water bodies.
(1) Dissolved oxygen. The change of dissolved oxygen in the water after icing is closely related to the species and quantity of phytoplankton in the pond, the number of aquatic animals, the sediment and the translucency of ice. Dissolved oxygen in ice water comes from photosynthesis of phytoplankton and submerged plants. The change trend of the amount of dissolved oxygen in the water during the ice-sealing period depends on the daily production of phytoplankton and the daily balance of oxygen consumption of organisms and sediments. If the daily oxygen production of phytoplankton is greater than the daily oxygen consumption of biological respiration and organic matter oxidation, the amount of dissolved oxygen in water will increase day by day; if the daily production of phytoplankton is less than the daily oxygen consumption of biological respiration and organic matter oxidation, the water The amount of dissolved oxygen decreases day by day. The amount of dissolved oxygen and daily net production in the water during wintering are closely related to the type and quantity of phytoplankton in the pool water and the transparency of ice. Green algae (Chlamydomonas, Chlorella, etc.), Chrysophyta (Brownella, Alpinia, etc.) and diatoms (Needle-shaped algae, Kestzella, etc.) have a high intensity of photosynthesis and a large amount of daily oxygen production. , Cryptophyta produces less oxygen. Bright ice is better than Wubing and snow-covered, so under the same conditions, the former produces more oxygen than the latter.
The change law of dissolved oxygen in the pond water with few phytoplankton is generally after the ice is sealed, and the dissolved oxygen in the water decreases day by day. Immediately after the ice is sealed, the amount of dissolved oxygen in the water can reach 11 mg/L~15 mg/L. Since the amount of oxygen consumed is greater than the amount of oxygen produced by photosynthesis, the amount of dissolved oxygen gradually decreases, which is the lowest before the ice melting, and sometimes drops to 2 Mg/L ~3 mg/L or less. This situation is very dangerous.
The vertical distribution of dissolved oxygen in wintering ponds is closely related to the transparency of pool water. When there are many plankton in the pool, the transparency is low, and the illumination under the ice decreases with the water depth. The oxygen production of phytoplankton in each water layer also decreases with illumination decreasing, and the organic oxygen in the bottom layer decomposes, so usually the surface oxygen is higher than the bottom layer. . However, when the transparency of the ice is good, the transparency of the pool water is relatively light, and the water is shallow, the light can be directly injected into the bottom layer. The phytoplankton in the entire water layer can normally perform photosynthesis, and sometimes the amount of phytoplankton in the bottom layer is more than the surface layer. At this point, the amount of dissolved oxygen in the bottom layer is often higher than the surface layer.
(2) Carbon dioxide. The carbon dioxide content in the water after the ice closure gradually increased. Carbon dioxide in water is mainly derived from the oxidative decomposition of organic matter and the breathing of aquatic organisms. Due to the accumulation of carbon dioxide, the amount of carbon dioxide in the water increases day by day. According to records, the highest concentration of carbon dioxide in the water during wintering is 174 mg/l (more than 60 mg/l of carbon dioxide in water is harmful to fish, and over 200 ml/l can cause fish to die; especially in the absence of oxygen, An increase in carbon dioxide will also accelerate fish mortality). This is very dangerous. Therefore, there must be a certain amount of phytoplankton in the water, and photosynthesis of phytoplankton is used to reduce the impact of carbon dioxide on water quality.
(3) Hydrogen sulfide. In the absence of oxygen after freezing, hydrogen sulfide is produced by the mineralization of sulfates and organic matter (proteins) in the reducing water under the action of reducing bacteria. Hydrogen sulfide is a toxic substance that is extremely toxic to fish. Even if the water contains very little hydrogen sulfide, it can cause fish poisoning and death. At the same time, its oxidation also consumes oxygen in water, and 1 milligram of hydrogen sulfide requires consumption of 1.4 milligrams of oxygen in water. Therefore, the amount of dissolved oxygen rapidly decreases in the water body that produces hydrogen sulfide. However, it rarely happens in the absence of oxygen.
(4) pH. After the ice closure, due to the accumulation of carbon dioxide, the pH will gradually decrease from weak alkaline to neutral or weakly acidic.
The change of physical and chemical factors of various water bodies is different. For water bodies with deeper water, less silt and less organic matter, the physical and chemical factors of the water body have less relative changes, and the over-winter safety factor is also high. On the other hand, water bodies with shallow water, thick silt, and high organic matter content have large variations in various physical and chemical factors, and the fish have poor wintering effects and are also dangerous.
During the winter of fish, dead fish occurs in the fish pond every year, but only at different levels. Therefore, in order to improve the survival rate of fishes in winter, the author studied the physicochemical and biological conditions of wintering waters of fish and the physiological changes of fishes during wintering, as well as the precautions for wintering in ponds and the management methods for overwintering. . This article will introduce the environmental conditions and technical characteristics of fish overwintering.
First, the basic conditions for wintering pool should have
1. The water depth should ensure that the wintering pool is not more than 1.5 meters above sea level. As the wintering pool is in the long-term freezing period, the pool water continuously leaks. Therefore, it is not enough to consider only the depth of water when entering the pond. Pay attention to changes in the water level in the wintering pond and take timely measures to make the wintering pond water within the required range. .
2. The bottom of the bottom pool should be flat, and the thickness of the sludge should be about 10cm. Because the sludge contains a large amount of humus, although it can play the role of fertilizer supply, fertilizer maintenance, and water quality regulation, excessive sludge will be decomposed during the process. Consuming large amounts of oxygen is prone to hypoxia. Therefore, the sediment in the wintering pond should be removed as much as possible.
3. Water quality Fish should not use old pond water for wintering, and it is better to blend in more than half of the new water. The transparency of the water should be greater than 35 cm. Keeping a certain amount of phytoplankton in the water, using photosynthesis under the ice and supplementing the oxygen in the water, can play a role in improving water quality.
4. Water source wintering ponds are preferably near the water source or use the surrounding fish ponds to store water to make up for the wintering pond if necessary. The water quality of the water source must meet the water standard for fish farming. If groundwater such as well water is used, it is necessary to try to increase the oxygen content and to increase its oxygen content and discharge harmful gases such as toxic hydrogen sulfide to ensure the safety of fish wintering.
There is no special requirement for the area of ​​the wintering pond, as long as the pool is convenient, the size can be, the best area is 10 acres to 20 acres.
Second, the main physical and chemical factors of winter water body changes
1. Water temperature ice overwintering pool ice water temperature often occurs vertical stratification phenomenon, near the ice water temperature is generally around 0 °C, down gradually increased, such as the depth of 1.5 meters above the water level of the bottom up to 4 °C. Winter fish are generally clustered in deep water. The vertical distribution of water temperature in wintering ponds is shown in Table 1.
If oxygenation measures such as circulating water or replenishing water are used, the natural vertical distribution of water temperature under ice will be broken down, and the water temperature at the bottom can be reduced to 0.2°C. When the water injection is stopped, the water temperature will naturally rise but the water temperature at the bottom will generally not reach 4 °C.
2. Illumination under the ice In addition to the thickness of snow on ice more than 50 cm, the water layer under the ice can have a certain amount of light. The degree of illuminance is closely related to the transparency of ice and the thickness of snow, but less to the thickness of ice. Bright ice, regardless of thickness, light transmittance of up to 30% or more, up to 63%. The ice transmittance is generally about 10% and the maximum is 12%. Snow cover 20 cm to 30 cm, the light transmittance is greatly reduced, only 0.15%. Binzhou, Shandong Province is not very cold in winter and its ice thickness is about 40 cm to 45 cm. It sometimes melts at noon and then freezes again. This ice ice has poor light transmission. Although the ice is not thick, the light transmittance under the ice is very high. reduce. If the snow can be cleaned in time during winter, maintaining a high light transmittance, the underwater illumination can basically meet the needs of algae photosynthesis. This is very beneficial to improving the quality of overwintering water and increasing the dissolved oxygen content.
3. Water quality The stocking density of the fish wintering pond is higher than that of the rearing pond. After the pool is frozen, the water is isolated from the air, creating a small environment that is not affected by the atmosphere. Therefore, the metabolic activities of fish and aquatic organisms and the decomposition of organic matter are all carried out in this small environment. Therefore, the consumption of oxygen and the generation of metabolic wastes will cause great changes in the physicochemical and biological conditions of water bodies.
(1) Dissolved oxygen. The change of dissolved oxygen in the water after icing is closely related to the species and quantity of phytoplankton in the pond, the number of aquatic animals, the sediment and the translucency of ice. Dissolved oxygen in ice water comes from photosynthesis of phytoplankton and submerged plants. The change trend of the amount of dissolved oxygen in the water during the ice-sealing period depends on the daily production of phytoplankton and the daily balance of oxygen consumption of organisms and sediments. If the daily oxygen production of phytoplankton is greater than the daily oxygen consumption of biological respiration and organic matter oxidation, the amount of dissolved oxygen in water will increase day by day; if the daily production of phytoplankton is less than the daily oxygen consumption of biological respiration and organic matter oxidation, the water The amount of dissolved oxygen decreases day by day. The amount of dissolved oxygen and daily net production in the water during wintering are closely related to the type and quantity of phytoplankton in the pool water and the transparency of ice. Green algae (Chlamydomonas, Chlorella, etc.), Chrysophyta (Brownella, Alpinia, etc.) and diatoms (Needle-shaped algae, Kestzella, etc.) have a high intensity of photosynthesis and a large amount of daily oxygen production. , Cryptophyta produces less oxygen. Bright ice is better than Wubing and snow-covered, so under the same conditions, the former produces more oxygen than the latter.
The change law of dissolved oxygen in the pond water with few phytoplankton is generally after the ice is sealed, and the dissolved oxygen in the water decreases day by day. Immediately after the ice is sealed, the amount of dissolved oxygen in the water can reach 11 mg/L~15 mg/L. Since the amount of oxygen consumed is greater than the amount of oxygen produced by photosynthesis, the amount of dissolved oxygen gradually decreases, which is the lowest before the ice melting, and sometimes drops to 2 Mg/L ~3 mg/L or less. This situation is very dangerous.
The vertical distribution of dissolved oxygen in wintering ponds is closely related to the transparency of pool water. When there are many plankton in the pool, the transparency is low, and the illumination under the ice decreases with the water depth. The oxygen production of phytoplankton in each water layer also decreases with illumination decreasing, and the organic oxygen in the bottom layer decomposes, so usually the surface oxygen is higher than the bottom layer. . However, when the transparency of the ice is good, the transparency of the pool water is relatively light, and the water is shallow, the light can be directly injected into the bottom layer. The phytoplankton in the entire water layer can normally perform photosynthesis, and sometimes the amount of phytoplankton in the bottom layer is more than the surface layer. At this point, the amount of dissolved oxygen in the bottom layer is often higher than the surface layer.
(2) Carbon dioxide. The carbon dioxide content in the water after the ice closure gradually increased. Carbon dioxide in water is mainly derived from the oxidative decomposition of organic matter and the breathing of aquatic organisms. Due to the accumulation of carbon dioxide, the amount of carbon dioxide in the water increases day by day. According to records, the highest concentration of carbon dioxide in the water during wintering is 174 mg/l (more than 60 mg/l of carbon dioxide in water is harmful to fish, and over 200 ml/l can cause fish to die; especially in the absence of oxygen, An increase in carbon dioxide will also accelerate fish mortality). This is very dangerous. Therefore, there must be a certain amount of phytoplankton in the water, and photosynthesis of phytoplankton is used to reduce the impact of carbon dioxide on water quality.
(3) Hydrogen sulfide. In the absence of oxygen after freezing, hydrogen sulfide is produced by the mineralization of sulfates and organic matter (proteins) in the reducing water under the action of reducing bacteria. Hydrogen sulfide is a toxic substance that is extremely toxic to fish. Even if the water contains very little hydrogen sulfide, it can cause fish poisoning and death. At the same time, its oxidation also consumes oxygen in water, and 1 milligram of hydrogen sulfide requires consumption of 1.4 milligrams of oxygen in water. Therefore, the amount of dissolved oxygen rapidly decreases in the water body that produces hydrogen sulfide. However, it rarely happens in the absence of oxygen.
(4) pH. After the ice closure, due to the accumulation of carbon dioxide, the pH will gradually decrease from weak alkaline to neutral or weakly acidic.
The change of physical and chemical factors of various water bodies is different. For water bodies with deeper water, less silt and less organic matter, the physical and chemical factors of the water body have less relative changes, and the over-winter safety factor is also high. On the other hand, water bodies with shallow water, thick silt, and high organic matter content have large variations in various physical and chemical factors, and the fish have poor wintering effects and are also dangerous.
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