Overwintering technology of fish in Northeast China
First of all, the pond is aging and has not been dredged for many years, and the silt is thick. The pig and duck manure from the pig and duck farm in Tangtou falls into the pond, and the fish (species) are cultured in high density, with high intake and excretion, increased organic matter and high oxygen consumption; Secondly, in some villages and towns, villagers live densely, and domestic sewage and wastewater from nearby factories are discharged into ponds, which consumes a lot of oxygen, resulting in insufficient dissolved oxygen; Moreover, excessive carbon monoxide, carbon dioxide and hydrogen sulfide in water will also cause fish (species) to die of poisoning; Fourthly, the fish pond has large leakage, poor water retention, insufficient fresh water supply, shallow water lack of oxygen in the pond and narrow fish activity space; Fifth, newly dug ponds and thin ponds are not fat, lack of abundant phytoplankton, weak photosynthesis, oxygen production is not equal to oxygen consumption, and fish die of hypoxia and floating head disease.
2. Fish species are too dense and too small to cause death.
Uneven size of fish species, coupled with improper feeding and law of the jungle, lead to fish species being too small, getting worse and worse in physique, and less energy accumulated by nutrients such as fat in the body, so it is difficult to maintain the energy needed for life activities during the long wintering period, and they die because of weak physique.
The fish died of injury.
Improper operation when pulling nets to market or assembling ponds will cause fish scales, fins and gill filaments to be scraped off, so that bacteria can invade and infect diseases and die easily during the wintering period.
4. Poor management leads to death
During winter, fish farmers think that fish don't eat or eat less feed, but relax management and don't check the water quality in time (when the oxygen content in water drops to 3 mg/L, fish feel uneasy; When the dissolved oxygen is 1 mg/L, fish have difficulty breathing and a large number of floating heads die. It is best to control the dissolved oxygen at 5 mg/L (safety factor). The water body is aging and the fish is active. Otherwise, if the fish is found to be in poor health and measures are not taken in time, the fish will weaken and die due to delay. Water leakage, shallow water and thick ice and snow in the wintering pool will all lead to hypoxia in the pool water, and will also lead to fish suffocation and death.
Second, prevention and remedy.
1. Establish the concept of "prevention first, treating both the symptoms and root causes"
Three conditions must be met for breeding animals to get sick: first, the breeding environment is bad (including abnormal climate); Second, aquatic animals are weak in constitution and their disease resistance is reduced; The third is the existence of pathogenic pathogens, all of which are indispensable. According to these three principles, if we can do well in these three aspects, we can make the cultured varieties overwinter safely. Therefore, we must adhere to the principle of putting prevention first and combining prevention with control, implement a healthy and ecological aquaculture management model, reduce or control the diseases of overwintering fish, and reduce the economic losses caused thereby, so as to lay a solid foundation for increasing production and income in the coming year.
2. Transform the overwintering culture environment
Choose the wintering pond, clean the pond and disinfect it to improve the water quality. The quality of overwintering ponds is directly related to the survival rate of fingerlings and the growth and growth of adult fish. Pond selection conditions: leeward facing the sun, good water retention, sufficient water source, convenient irrigation and drainage, 3-5 mu of fish pond, 5- 10 mu of adult fish pond, and 2-3 meters of water depth (the water level in the northern pond should be kept at about 2 meters after freezing). If possible, choose a pond with hot spring water, which is most conducive to protecting tropical and subtropical fish for the winter. Excess sludge should be removed and used as organic fertilizer for crops and fruit trees, and leakage should be repaired. The bottom of the pond should be cleaned, and the sludge should be kept 20 cm, and exposed to the sun, raked up and fully oxidized. Then pour water into the pond 80 cm ~ 100 cm, put 150 kg of quicklime and 50 kg of tea bran into the pond (after soaking for 24 hours, evenly splash the residue and water into the pond), so as to neutralize the acidity of the quicklime, raise the pH value, improve the water quality, release nutrients and kill wild fish, parasites and pathogens. Tea bran can not only kill wild fish, but also improve water quality (cultivating abundant phytoplankton is beneficial to photosynthesis and oxygen production). In addition to medicinal properties, tea bran is also a nutritional bait that fish like to eat. A week later, the water level in the wintering pond was deepened to 1.5m ~ 2m, and 500kg fermented organic fertilizer (or 5kg urea and 3kg phosphate fertilizer) was applied per mu to improve the water quality, so that fish species (or adult fish that cannot be marketed after pond splicing) could eat rich bait after falling into the pond.
3. Improve the overwintering and cold-resistant immunity of fish (species).
Large fish species are physically strong, fat, cold-resistant and anoxic, and have strong anti-infection ability. According to the author's practice for many years, under the same conditions, the survival rate of fish with tail length 12 cm or more can reach 90% after wintering, while the survival rate of fish with tail length of 5 cm ~ 6 cm is 50% ~ 60%. It can be seen that every autumn, fish eat a lot and accumulate fat energy for wintering consumption, so it is necessary to feed more high-protein and high-fat feeds (such as agricultural and sideline products, peanut bran, bean cake, wheat bran, jade bran and appropriate fresh green leaves and grass leaves) to fatten fish (species). Timely release is to grasp the release time, premature release, high water temperature, frequent fish activities, high oxygen consumption and physical exertion, and the scratch of the net is also prone to diseases such as red skin and rotten cheeks; If the fish is released too late and the weather is cold, pulling the net to scrape the fish will also damage the fish's body surface, which will easily lead to water mold infection and a large number of deaths. Therefore, pond culture with water temperature between 1 12℃ and 15℃ in the middle of 10 is generally selected (at this time, fish activities are weakened, scales are dense, and it is not easy to scratch and get sick when pulling nets). There are single species and multiple species of fish (fry), which should be divided into varieties, specifications and feeding habits. Such as filter-feeding silver carp and bighead carp, can make 70% of cultured fish, 20% of grass carp and 10% of bottom omnivorous fish (single species of tilapia or shad, etc. ), and vice versa. If you are cultivating bottom fish (tilapia, shad, carp, crucian carp, etc. ), don't mix them, because these fish have similar feeding habits, live in the water layer, and are easy to grab food. The big fish bully the small fish, causing the weak to die first. It is suggested that the single species cultured in a single pond should be mainly fish of the same specification, such as shad (70%), silver carp (20%) and grass carp (65,438+00%), which can make full use of the fish food chain, benefit each other and cultivate healthily. Over-stocking, due to insufficient feed for food, fish grow in different sizes, have small activity space, and the water level drops, which is easy to die of hypoxia; Too sparse, wasting water space. Generally, 30,000 ~ 40,000 fish species with a height of 10cm are released per mu, and less than 10000 are released per mu without supplementary water. In the case of adult fish ponds, generally 300 kg of adult fish can't be listed, as much as you can catch, so as to keep the fish quantity relatively stable, which is conducive to increasing production and income. It should also be adjusted in time according to the specific conditions of breeding technology, feed, water source, variety, specification and density, and cannot be copied. Stocking is carried out at 2 ~ 3 noon when there is no wind, light and normal water temperature. Quarantine before stocking, soak the fish in 4% ~ 5% salt solution, disinfect for more than ten minutes, and then go to the pond for culture.
4. Strengthen overwintering management
Do a good job in water quality management: patrol the pond regularly to observe the changes of water color in the morning, noon and evening, so as to make the pond water "fat, lively, tender and cool", inject new water regularly (18 days ~ 15 days) and discharge old water. If the water quality is found to be discolored, turbid, black and fishy, it means that the water quality is getting worse and new water needs to be replaced in time; If there are concentrated activities of fish in the ice eye, it is necessary to break the ice in time and replenish fresh water or adopt other methods to increase oxygen. After snowfall, the surface of the frozen pond should be cleared of snow, the lighting conditions should be improved, the photosynthesis of phytoplankton in the water should be increased, and more oxygen should be produced. Feeding culture should be relatively reasonable, not only to ensure that the fish (species) are full, but also to consider the pollution of the breeding environment and save costs, so scientific feeding is necessary. 1~ feed once every two days 1% ~ 1.5% in the morning 10 for several times, feed less when the water temperature is lower than 15℃, and feed less when it is lower than 8℃; Feed more when the weather is warm and sunny, and don't feed when the wind and rain are light; Don't feed when floating, feed more when the water quality is good, and don't feed when the water quality is poor. Feed nutrition should be reasonable and comprehensive, and it is better to add some minerals and vitamins.
Do a good job in the prevention and control of fish diseases: give priority to prevention and combine prevention and control. In the process of culture, some water quality improvers, matrix improvers and microbial agents are often used, and the effect of using live bacteria is better and the water quality is better. Regularly disinfect the aquaculture water, sterilize and kill insects, and cut off the horizontal transmission of pathogens. It is best to use disinfectants (such as bleaching powder, salt, quicklime, yujunjing, yujunqing, etc.). And the bait is regularly fed to enhance the physique of fish and improve the abilities of disease resistance, cold resistance and overwintering. The overwintering fish pond should be kept quiet to prevent livestock from falling into the pond and disturbing the fish.
Do a good job in cold and antifreeze: although fish are temperature-changing animals, when the water temperature drops to 1℃ ~ 0℃, warm-water fish generally enter a state of paralysis; When the water temperature drops below 0.5℃, the fish will die immediately. Due to the geothermal heat, the water temperature in overwintering fish ponds is generally around 4℃, and fish bodies such as "Four Big Fish" will also die due to large-scale frostbite and infection with diseases such as water mold and bacteria. However, tropical and subtropical fish will also die in large numbers when the water temperature is 6℃ ~ 10℃, and water mold caused by frostbite at 12℃ ~ 18℃ will also die in large numbers. Therefore, the water level in wintering fish ponds should be deepened to 3m as far as possible, or a frost-proof shed with a depth of 60m2 ~ 80m2 should be set up in the leeward and sunny part of the fish ponds, and straw or nylon woven cloth with a thickness of 10cm ~ 13cm should be covered above the water surface with bamboo poles, or peat mud and straw prepared at ordinary times should be piled around the pond foundation, and attention should be paid to the weather forecast. Once the cold wave comes, light it.