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Temperature-water fish (such as tilapia, squid, pond gizzards, gemstone clams, freshwater white clams, etc.) are poor in resistance to low temperatures. When the water temperature drops to its critical lethal temperature, insulation measures must be taken or the fish will freeze. After death, even if it is not frozen, the fish body can easily induce infection and mass death after frostbite. Therefore, we must take the necessary cold measures to ensure that they safely overwinter and avoid or reduce losses.
First, anti-cold antifreeze technical measures
1. Cut off alternating flow caused by convection and wind in different temperature layers of the pond.
In winter, the temperature of the rainwater is relatively cold, which is significant, and it is easy to sink and accelerate the cooling at the bottom of the pond. In addition, the strong northerly action in the winter will cause the pond water surface and the bottom of the pond to alternate slowly, so that the water temperature at the bottom of the pond will drop rapidly. Therefore, cutting off alternating flow caused by convection and wind in different temperature layers of the pond can effectively prevent the decline of pond water temperature.
(1) Wintering technology for plastic insulation greenhouses When the pond area is relatively small and is suitable for the construction of a whole pool of plastic film greenhouses, ponds with high topography, good water retention, and leewardness should be selected as wintering ponds. Ponds can be earthen or cement pools. The whole pool is supported by arched frames with steel pipes or wood, covered with plastic film, and covered with a layer of sparse mesh to prevent the wind from blowing the film. The part of the membrane connected to the pool edge is sealed with slime. Greenhouses should not be too high, about 60-80cm above the pond, generally half-slope. The pond water depth is 2.5-3m, and the pond base is 20-30cm above the ground. It is equipped with simple temperature-increasing and oxygen-increasing facilities. In places where groundwater can be exploited, underground water can be extracted from deep-water wells to keep the ponds at a certain temperature and help aquatic animals to safely pass winter. When the temperature rises, some of the membranes must be opened to allow air to circulate, so as to avoid the death of oxygenated animals.
(2) Simple half-shed wintering technique When the pond area is large and the construction of the greenhouse is not easy, put a stake on both sides of the north 1/3 of the pond, pull on the steel wire rope, or use bamboo to cross over the surface of the fish pond. About 0.5m, covered with film to prevent the cold rain from sinking. This has an endothermic effect during the day and slows down the heat at night. In addition, the film should be covered with a sparse net to prevent the wind from blowing the film. At the same time, ditches should be dug around the pond to prevent the inflow of snow from the pool and reduce the pool water temperature. This method can prevent the pond from freezing and locally increase the pond water temperature. This method is simple and the material can be used repeatedly for 4-5 years.
(3) The semi-wall wind-resisting and cold-resisting technology can construct a wind shield on the north side of the pond to block the north wind from blowing directly onto the surface of the pond and slow down the alternation of the pool water, thereby slowing the cooling of the pool water. The windshield is about 2-3m high. It is built with bamboo, mixed wood or other materials. It is then covered with a film or straw to block the cold wind and reduce the water temperature in the pond.
2. When the temperature in the greenhouse or the greenhouse is too low, the temperature may be increased by burning carbon or diesel in the room or shed.
3. Increase the water depth of the pond and keep the water depth at 2m or more. Or you can dig a fish ditch 8-10m long, 4-5m wide and 2m deep in the west and north sides of the fish pond. When the cold wave arrives, fish can be concentrated in the fish ditch to keep warm.
4, rare species of small water, can increase the salinity of the water, so that the salinity of the water in the 2-3 ‰ (depending on the species may be), can increase the cold resistance of fish and shrimp 1-2 °C.
5. When there are conditions, use hot water pipes to inject hot water or hot spring water at the bottom of the pond to form a heat island at the bottom of the pond, which will help the fish accumulate winter.
6. For larger ponds, it is also possible to adopt a method of concentrating overwintering. Through the separation and insulation of the local waters of the pond (such as the corner of the pond), the aquatic animals gather for the winter.
Second, the management approach
1. During the cold spell, water should not be added because the water level of the pond is too low to prevent the fish from freezing to death due to stress.
2, open-air ponds can not be warmed with the sun lamp at night, because the lights will lure the fish to the surface of the pond in the low-temperature area and frostbite, easy to cause watery mildew and death.
3. Firecrackers or pool water should not be thrown at the pond to avoid fish being frozen to death.
4. If there is no pond with a warm greenhouse, the aerator should not be started as much as possible to reduce the convection of the pond water, thereby slowing down the water temperature drop at the bottom of the pond and achieving the purpose of preventing cold.
5, the construction of a greenhouse shed, overwintering shed turbid air, it is appropriate to open more aerators, rushing groundwater to keep the water fresh and adequate dissolved oxygen, to prevent the death of fish oxygen-free floating head. In the late winter, when the temperature rises, the overwintering shed film should be opened to remove harmful gases (such as carbon dioxide, hydrogen sulfide, etc.) from the shed, which will facilitate the convection of air inside and outside the shed and improve the dissolved oxygen in the water.
6. If the surface of the pond has been frozen, the ice layer within the range of 3-4m near the pond should be smashed as soon as possible to prevent the lack of oxygen in the aquatic animals and at the same time be conducive to the escape of some harmful gases in the water. In addition to pay attention to the color of ice, ice should be better, if the ice color is too deep, it will lead to insufficient light under the ice and affect the photosynthesis of phytoplankton in the water, resulting in fish hypoxia.
7, carefully inspect greenhouses and other insulation facilities and oxygenation and heating equipment. Completely reinforce and repair insulation and heat supply and aeration facilities to prevent seepage of rain and water in the fish ponds. Warming, temperature-building sheds and other insulation measures can be adopted in places where conditions permit.
8. When winter cold current increases, quick lime 15kg/mu (1.5m water depth), or bleaching powder 0.5-0.75kg/mu (1.2m water depth) may be properly applied to prevent the occurrence of diseases such as watery mildew.
9. If there is fish frostbite, apply 0.4 kg/m3 of salt and baking soda mixture as soon as possible to prevent saprophytic disease.
10. Try iodine preparations for the treatment of diseases such as small melon worms and water mold caused by low temperatures.