Common diseases and countermeasures for the artificial cultivation of yellow eel in China
1 Status of yellow eel culture
Artificial cultivation of yellow eel in China began in the early 1980s and has been expanding in recent years. With the expansion of the scale of breeding, the disease of yellow eel is becoming more and more serious, and the currently found yellow eel diseases mainly include bacterial diseases, fungal diseases and parasitic diseases. Yellow eel bacterial disease mainly includes hemorrhagic sepsis, enteritis, etc., and the pathogens are aeromonas, mild aeromonas, pseudomonas alkaline and so on. There are 15 species of parasites reported in China, and a large number of investigations have been carried out on the epidemiology of the yellow eel parasite, and the relationship between different water bodies, seasons and parasitic infection rates has been analyzed.
Seasonal variations in fish parasitic helminth infection levels are related to water temperature and parasite life history, and parasitic worms in fish are usually infected by feeding on intermediate hosts. The peak of hidden new echinococcal infection occurs in spring and autumn, and the peak of infection of gastric nematode in yellow eels is in late spring and early summer. Parasitic infection is related to the individual size of the yellow eel, and the infection intensity of the new echinococcus increases with the increase of the individual. The jaw-mouth nematodes in the yellow eel parasite can infect humans.
2 Prevention of yellow eel diseases
There are many ways to diagnose yellow eel disease, visual examination is the main way to check yellow eel disease, common eel disease sites are mainly manifested in the body surface and internal organs. In order to determine that it should be observed on the spot, the diseased eels are fished out of the eel pond in time, and carefully observed from the head, eyes, eel tail and other parts in order, and large pathogens can be found from the body surface, and small pathogens cannot be seen by the naked eye. It can be distinguished according to the pathology, such as the eel body is blue and black, the redness and swelling are prominent, and it is mostly enteritis. Local bleeding on the surface of the eel, in severe cases, the epidermis is a funnel-shaped small socket, and the epidermis rots into erythroderma; The surface of the body is covered with mud and is covered with mud for mud dragging disease. Dissect the eel, cut the foregut to the hindgut, observe for the presence of parasites, rinse with water, and if intestinal congestion is found, it is enteritis.
When stocking eel seeds, it is best to use potassium permanganate and other drugs for in vitro disinfection, and all localities should be adapted to local conditions. When soaking, it is necessary to achieve the required concentration of the liquid medicine, depending on the tolerance of the eel seed. Eel species captured in the wild or cultivated in special ponds are soaked with 2% salt water for 10 minutes before stocking, and then put into eel ponds to achieve the purpose of disease prevention. Pay attention to thoroughly clean the pond before stocking, use 50g of quicklime slurry per square meter and sprinkle it, and then release the eel seed after 5 days. Avoid touching the eel body with dry tools during stocking operations to ensure that the eel body has a certain degree of wetness, and do not use force to squeeze the eel when catching yellow eel.
3 Common diseases of yellow eel farming
Common ecological diseases are spasticity, colds, and fever. Spastic disease is currently the most threatening disease of artificial breeding of yellow eels, the disease is manifested as extreme head spasms, easy to frighten, often unconsciously bitten. There is no inflammation on the surface of the body and internal organs. It is often developed in batches, and death begins after 10 days and ends after 1 month.
When changing water, the water temperature difference exceeds ±2 °C may lead to a cold, and the water temperature difference changes suddenly, making it difficult for the normal movement physiological regulation of the eel body to adapt to the change of temperature outside the body, and the occlusion of the thermoregulation pathway leads to a cold. Fever also occurs mainly in transport, due to the long transport time, the body surface mucosa is decomposed by microorganisms in the water, resulting in a sharp increase in water temperature, so that the head of the underlying yellow eel is swollen, and the mortality rate of this disease can reach 90%.
Common diseases of bacteria are printing disease, enteritis disease and water mold disease. Print disease is infected by the punctate subspecies of the pathogen Punctate Aeromonas, which initially appears small erythema at the wound, and then expands to a round bean size, with congestion and redness at the edges; In severe cases, bones and internal organs can be seen, and the diseased eel does not enter the hole, and dies of exhaustion.
Enteritis is caused by a digestive tract infection caused by the consumption of spoiled food in yellow eels, which has a decrease in appetite, slow movement, and prominent redness and swelling. Water mold disease is caused by infection due to improper handling of body surface injuries in the early stages of stocking.
Parasitic diseases are common and include spondylosis, cryptoflura, black spot disease, and capillary worm disease. Vertebral worms parasitize in the blood of yellow eels, which are often anemia and have poor growth after infection. Cryptoflagellum parasitizes in the blood of yellow eels, after which the flagella is attached to a section of the body surface of the insect, the living insect body flutters in the blood, and the infected yellow eel is anemia-like, which is more common in summer and autumn. Black spot disease is caused by the parasitism of the posterior cysticers of the compound mouth fluke in the subcutaneous tissue of the fish body, and small black dots appear on the tail at the beginning of the disease, followed by the color of the small dots deepening, some small black dots protruding into the skin, and the diseased eel stops feeding until it dies. Spinosa is caused by the parasitism of a hidden new echinoccans in the foreguin of the yellow eel, with a cylindrical cylindrical body and a small snout. Sick eels have intestinal obstruction due to a large number of parasites, loss of appetite, and are manifested by a large head and a small tail. Causes death in severe cases.
Capillary nematode disease is caused by capillary worm parasitism in the second half of the yellow eel intestine, often due to water change is not infected in time, the diseased eel is reduced and emaciated, parasitic locusts on the body surface, because the ant adsorbed on the surface of the yellow eel, the diseased eel is slow, affecting normal growth. Cultivating water hyacinth in the pond is beneficial to the effect of yellow eel culture, but it is easy to bring in ants.
4 Control of diseases in yellow eel farming
4． 1 Prevention and control of common diseases
Quicklime clear pond for the prevention and control of spondylosis, and the effect can be seen by soaking the diseased eel in 20g/L of salt water for about 10 minutes. Cryptolera control is effectively prevented with a 5min bath in a 20 g/L salt water solution. Quicklime clearing ponds for the prevention and control of black spot disease, sprinkle the whole pond with 1~15mg/L algae and insect clear liquid, with 0. 6 mg of bacteria and algae net whole pool sprinkled.
Echinococcal disease was controlled with 2 mg/L 100 g of solution to soak the diseased eel for 5 minutes, and added to the feed with 40% of the addition of fish worm no. 1, and the bait was fed in 3 times for 1 day. Broad-spectrum insecticides are fed regularly. For capillary nematode disease, soak the diseased eel with 2mg/L 100 grams of worm solution for 5 minutes, add it to the feed with fish worm extermination No. 1 in 4% amount, feed the bait in 3 times for 1 day, and stop eating for 1 day before taking the drug.
Parasitic locust control on the surface of the body puts the diseased eel into a 100-gram worm solution bath for 5 minutes, and soaks it in 5 parts of each yellow eel for 2 hours. If it is found that the yellow eel trembles during the bath, indicating that the drug concentration is too high, the yellow eel should be fished out immediately. Lay out 3 handfuls of tobacco leaves in the breeding pond to free the locusts from the eels on their own.
4． 2 Prevention and control of other diseases
The pathogen of bacterial sepsis is waterphilic monastic bacteria, etc., and the diseased eel floats on the surface of the water, does not eat, and appears on the surface of the body with erythema of different sizes. Some of the sick eels had red and swollen heads, followed by a large number of deaths. Extensive bleeding from internal organs may be seen on autopsy. The epidemic area is wide, and the peak period is in autumn, showing the characteristics of rapid incidence and high mortality. The control method is to thoroughly clear the pond with quicklime, avoid damage during cage fishing, adopt appropriate stocking density, and monitor water quality. To prevent pathogenic bacteria from entering, eel seeds are sterilized with 3% salt water for 5 minutes when stocking, and with internal medication, Chinese herbs such as pentaplus and forsythia can be added to the feed for feeding.
Printing pathogens are point-like aeromonas, etc., the surface of the sick eel appears to varying degrees of lump rot, the initial diseased eel has a loss of appetite, the back of the body surface is inflamed and congested, and in severe cases, the ulcer lesion is deeply concave, such as a red seal mark. This disease is the main disease of the adult stage of yellow eel, mostly occurs in summer and autumn, has a strong contagiousness, and the natural healing rate of the diseased eel is extremely low. Prevention and control method is to prevent mechanical damage during transport, when the printing disease is found, 2 toads are caught by caesarean section, and a rope is tied to the toad's legs and repeatedly dragged in the pool. Sprinkle the whole tank with 2mg/L pentaplate solution, and feed with 100kg of yellow eel with 2g of sulfonamide methoxypyrimidine powder. Yellow eel is a partial carnivorous fish, artificial breeding long-term intake of high-protein food, water quality is easy to deteriorate, yellow eel greed leads to liver digestion and other functional overload, hepatobiliary enlargement and other diseases occur in autumn. The prevention and control method is to stop eating for 1 day after each feeding 7 days to reduce the liver load, reasonably feed the yellow eel, and sprinkle photosynthetic bacteria on the bottom of the cage in the whole pond to purify the bottom of the cage, so that the aquaculture water environment remains in good condition.
