Wintering management is an important part of pond culture and must be highly valued and actively promoted successful overwintering management experience to ensure safe wintering of fish. Key technical measures are described below.

First, adjust the water quality

The northern region generally stopped feeding in mid-October. After a 6-month breeding period, the pool water was dark in color, low in transparency, decreased in pH, and low in dissolved oxygen. There is a large amount of organic matter such as residual baits, fish droppings, and bodies of aquatic animals and plants in the water. Thickening of sludge at the bottom of the pond, increased oxygen consumption and accumulation of toxic or harmful substances, such as NH3, H2S, CO2, etc., increase the toxicity of fish. Adjusting the water quality can change the ecological environment of the pond and prevent the water from further aging. The main way we regulate water quality is to change the water. When water is changed, the bottom water is discharged first, which can effectively reduce the content of organic matter and harmful substances, and take away part of the mud. The discharge accounts for 2/3 of the water, and then the groundwater is injected to the highest level. Groundwater has very few organic matter and harmful organisms and it is suitable as a source of fish for wintering. The time for changing water is best to end at the beginning of December. If it is too early, it will increase the wintering load of the water body, and later it will freeze fish and even freeze the water supply facilities.

2. Kill zooplankton and reduce oxygen consumption factor

The pond water and zooplankton in the later period of culture have a high content, and they must be killed because of their high oxygen consumption rate. We took 0.35ppm crystals of trichlorfon to kill zooplankton and parasites. When splashing, it is best to use the water to dissolve. If the water is heated, the temperature of the water in the barrel cannot exceed 40°C. For ponds with large areas and inconsistent artificial splashing, it is necessary to row boats to ensure uniform distribution of drugs. Splashing Trichlorfon is best combined with changing the water. When the water level is at the lowest level, the dosage can be reduced and the cost can be reduced.

Third, fertilization and biological oxygenation

After the pond is frozen, the only source of dissolved oxygen in the fish pond is the photosynthesis of phytoplankton. The oxygen content of the water is closely related to the type and quantity of phytoplankton. In order to meet the needs of phytoplankton for nutrient elements and increase phytoplankton biomass, so as to enhance photosynthesis and increase dissolved oxygen, we adopted the fertilizer hanging bag method and carried out this work every January or early February. The specific approach is: 2 to 3 bags per acre of water, 3 to 3.5 kg of urea per bag, fertilizer bags made of 40 to 60 mesh sieve or white plastic woven bag. The fertilizer bag is suspended from the water surface and is about 10cm away from the ice. The distribution of chemical fertilizer bags should be even and the layout should be reasonable. According to our analysis, after 7-10 days, the water-soluble oxygen content of the pool can reach 5-11 mg/L.

Fourth, remove the snow

The area of ​​pond ice is snow, the water lacks light, and the photosynthesis of phytoplankton weakens. The source of dissolved oxygen is reduced. When the oxygen in the water is reduced to a level that does not meet the minimum physiological requirements of the fish, the fish suffocate and die. For example, the suffocation range of salmon and trout ranges from 0.1 to 0.4 mg/L. Therefore, remove the snow from the ice as soon as possible and allow the light to pass through the ice. Last year's three snowfalls in winter caused many fish farms in our region to suffer. The reason for the large number of overwintering fish deaths is that, apart from other technical measures that are not in place, the lack of timely removal of snow is one of the main reasons. When clearing the snow, sweep a 2m wide channel every 1m, especially the area where the fertilizer bag is hung, be sure to clean it. Conditional farms can be cleared in large areas or in whole pools.

Fifth, persist in watching the pond and take timely remedial measures

In winter, the water temperature of the water body is low and high, there is an inverse stratification phenomenon, and the fish stay in the bottom layer. Under normal circumstances, no fish activity can be observed through the ice layer, and it is easy for people to have numbness thoughts. In fact, the decline in dissolved oxygen in winter is relatively slow, unlike the sudden changes in summer, but it is gradually coming. Therefore, it is necessary to insist on daily inspections of the ponds in the early morning and carefully observe the fish activity under the ice and find problems and take timely measures. When watching the pond, special attention should be paid to observing the surrounding area of ​​the pond and finding signs of lack of oxygen as soon as possible. Conditioned farms can regularly measure dissolved oxygen levels and provide accurate data. In general, remedial measures include injecting groundwater, quickly opening part of the ice, installing submersible pumps to circulate water, and starting aerators.

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