Relationship between disease of eel culture in soil pond and water environment

Water environment is the decisive factor for eel culture. Water environment not only determines whether eel can be cultured, but also directly affects the yield and ultimately affects the economic benefits of eel culture. Therefore, only by improving the water environment can eel be raised well. The relationship between eel diseases and water environment is analyzed from the following aspects.

I. pH

pH value in water is an important comprehensive water quality index, which directly affects the physiological status of eel. Changes in the biological, chemical or physical composition of the water will be reflected in the pH value, and the pond eel requires that the pH value of the pond water be maintained between 6.5 and 8.5. If the pH value of the water is less than 6.5 and acidic, it will cause acidosis of the eel, causing protein denaturation, causing the loss of function of the tissues and organs and death; when the pH value is greater than 9.0, the water is alkaline, which has strong corrosiveness to the eel and causes serious damage to the eel gills. Acid and alkali water can stimulate eel gills and skin sensory nerve endings, reflexively affect respiratory movement, so that eel oxygen uptake ability from the water body is weakened, therefore, even if eel in oxygen-rich waters will appear hypoxia.

Control measures: When the pH value is less than 6.5, it can be adjusted with 30 g/m3 quicklime, or the pH value can be increased with "microecological promoter". If the pH value is greater than 9.0, the water should be changed immediately, or the whole pool can be sprinkled with bromochlorohydantoin, dibromohydantoin or mono-stable chlorine dioxide at a concentration of 0.2~0.3 g/m3.

II. Dissolved oxygen

Dissolved oxygen in water is an important environmental condition for eel survival and growth. It mainly comes from photosynthesis of phytoplankton. Hypoxia is detrimental to eel growth, affecting feeding, growth and feed utilization in mild cases, and reducing disease resistance and death in severe cases. The requirement of eel for dissolved oxygen should be kept above 4 mg/L. The causes of low dissolved oxygen are: first, high temperature, large activity and oxygen consumption of eel; second, excessive stocking density, large respiration of eel; third, decomposition of organic matter and oxidation consumption of inorganic matter in the pool.

Control measures: reasonable mix of mixed culture varieties and stocking density, the most ideal stocking density of soil pond is: 20P/kg for 2500~3500 per mu, 30P/kg for 3000~4000 per mu. Management personnel are required to regularly determine dissolved oxygen every day. If dissolved oxygen in water is insufficient, an aerator should be used in time. The use time of aerator should be determined according to weather changes. If the water color is really aging, fresh water should be injected or 80~ 150g of unified stable chlorine dioxide should be sprinkled in time.

III. Water temperature

Water temperature directly affects the metabolic intensity of eel, thus affecting eel feeding and growth. The adaptive temperature range of pond eel is 20~28℃. In this range, the metabolism of eel is enhanced correspondingly, the food intake is increased, and the growth is accelerated. On the contrary, eel metabolism weakened, immunity decreased, disease and even death. On the other hand, all kinds of pathogenic microorganisms reproduce under certain water temperature conditions, resulting in epidemic diseases. For example, European eel running disease generally occurs in summer high temperature, water mold is prevalent in winter and spring low water temperature.

Prevention and control measures: ① feeding fresh and high-quality bait;② in the climate change, water temperature and dissolved oxygen fluctuations, should reduce the amount of bait, pay attention to water quality control, in the whole breeding period should take "three adjustment" measures, that is, adjustment, adjustment;③ in the eel feeding season, should add some stomach powder, Lidan Baoganning, Jundu powder, a variety of vitamins, garlic or Chinese herbal medicine, such as stomach digestion and anti-inflammatory detoxification preparation mixed orally.

IV. Thoroughly clean up pond sediment and silt

Cleaning up pond sediment and silt is the basis of creating a good breeding ecological environment. Pond organic matter and humus sludge are often the main sources of deterioration and disease induction. Studies have shown that too much silt tends to deteriorate water quality, increase acidity, and bacteria tend to multiply in large numbers. At the same time, eel resistance is weakened in bad environments, so diseases are prone to occur.

Control measures: The newly constructed soil pond should be soaked in water before seedling release, the water depth should be maintained at 50~70 cm, the water should be changed 2~3 times a week, and the water added each time should not exceed 20 cm, so that the pH value is stabilized between 7.0~8.4. If it is an old pond, it must be strictly and thoroughly cleaned of silt, ploughed or exposed to the sun. If conditions permit, it is best to use bulldozers to push out 10~20 cm of sediment to transport the dike, and then in addition to applying 75~100 kg of quicklime per mu, 0.1 ~ 0.2 kg of bleaching powder or 0.1~0.2 kg of stable chlorine dioxide per mu can be applied to the whole pond to kill enemy organisms. The disinfected soil pond shall be soaked in water filtered by 60~80 mesh sieve, drained after 3~5 days, repeated for 3~5 times, refilled with new water after thorough disinfection (disinfection of new soil pond shall be carried out in the same way), and 5‰~7‰ salt shall be added into the new water to prevent virus transmission.

V. Ammonia nitrogen, hydrogen sulfide and nitrite

Ammonia comes from pond sediment and a large amount of organic fertilizer into the pond and eel's own excrement, produced by nitrification, it is a toxic substance for eel, can destroy gill tissue, and penetrate into the blood, reduce the oxygen carrying capacity of blood, so that respiratory function decreases.

Hydrogen sulfide comes from sulfate reduction bacteria in bottom sludge to sulfate, and organic sulfide in residual bait or feces is decomposed by anaerobic bacteria, resulting in black sludge, which is an important indicator of hydrogen sulfide existence.

Nitrite is a product of ammonia during nitrification. It is an important cause of eel disease, which is caused by high summer temperature, a large number of animal and plant carcasses, eel feces and residual bait deposition bottom decomposition, production of ammonia nitrogen, hydrogen sulfide, nitrite and other toxic substances, so that water quality deterioration, causing eel hypoxia or poisoning death. In addition, organic phosphorus poisoning is easily caused by drug abuse or improper water source in ponds. Control measures: For aquaculture ponds with a depth of 1~1.5 meters, 0.1~0.2 kg of unified stable chlorine dioxide or photosynthetic bacteria are sprayed on the whole area per mu, generally 1~2 times per month. This medicine can not only effectively kill these pathogenic microorganisms, but also react with hydrogen sulfide and organic matter in water, so as to achieve the purposes of deodorizing, bacteriostatic disinfection, ammonia reduction and oxygenation, improving substrate quality and purifying water quality, and preventing various diseases.