Prevention and control of diseases of farmed eel

Eel nematode disease [pathogen] is eel nematode. There are three species of eel nematodes parasitic in the swim bladder of eel: spherical eel nematode, thick eel nematode and Australian eel nematode. The eel nematode is oviparous, the newly born larva is only 0.2 mm-0.35 mm, the body is covered with a transparent surface membrane, and the tail is slender.

[symptoms and diagnosis] the eel nematode mainly lives on the eel's blood. The growth of diseased eels infected with nematodes is affected due to poor food intake. It shows anemia, emaciation, black body color and other body diseases. The swim bladder of diseased eel was swollen, the internal organs were oppressed, the blood flow was blocked, and the swim bladder tissue was inflamed. The sick eel floats so high that it is not easy to sink, gradually lose weight, and eventually die. Severe infection can cause the wall of the eel to break and the nematode to enter the abdominal cavity, causing peritonitis and killing the eel. [epidemic and harm] Eel nematode disease is prevalent in eel farms in Taiwan, Guangdong, Fujian, Zhejiang, Jiangsu and other provinces. The infection rate of the disease is very high, and a large number of deaths are generally very few. The disease occurs all year round, but it is more from June to September. [prevention and treatment] (1) Lime or bleach can kill larvae and intermediate hosts and has a preventive effect. (2) Trichlorfon (90% crystal) was sprinkled on the whole pond with the final concentration of 1 mg / L water, which had a better control effect. (3) to give antibiotics to prevent bacterial infection. Edwardsiasis [pathogen] Edwardsiella tarda. The growth temperature is 12-42 degrees, and the PH value is 5.5-9. It can grow in the range of 0-4% salt. [symptoms and diagnosis] according to the symptoms and pathological features, the disease can be divided into two types: liver type and kidney type. Liver-type symptoms: mainly manifested in eel anterior abdominal swelling, congestion or bleeding, abdominal wall muscle necrosis, skin softening. In severe cases, the anterior abdomen is perforated and the liver is exposed. Anatomical observation showed that the liver was enlarged with white purulent lesions. The main symptoms of renal type are as follows: prominent redness and swelling of the anus, enlargement of the kidney before and after the anus, muscle necrosis, skin congestion, extrusion of purulent blood from the abdomen. Anatomical observation showed enlargement of spleen and kidney and small purulent lesions. In clinical diagnosis, the typical symptoms of the disease should be grasped. The eel suffering from the disease has swelling, redness, softening, muscle necrosis, and even ulceration and perforation in the front and back of the abdomen or anus. [epidemic and harm] the disease is prevalent in eel farms in Japan, Taiwan and southeastern coastal provinces. In particular, a week or so after feeding the "red worm", Bai Zai is most likely to have an acute epidemic, causing a large number of deaths. [prevention and treatment] Prevention is mainly to strengthen feeding management, pay attention to the regular removal of residual bait and fecal dirt, appropriately increase the amount of water exchange, keep the water quality clean, the stocking density should not be too high, and feeding red insects should be cleaned. (1) every ton eel was fed with fish Kang B-II50 g-100g, evenly mixed with bait once a day for 3-5 days. (2) each ton of eel was fed with 200 grams of sulfamethoxazole mixed with bait, and then 100 grams per day for 5 consecutive days. Bacterial Gill rot disease [pathogen] Campylobacter columnar. The growth temperature is 5-35 degrees, the optimum temperature is 27-28 degrees, and the growth pH range is 6. 5-8. 5, and the optimum pH value is 7. About 5. The water body contains 0. 7% salt can inhibit its growth. [symptoms and diagnosis] the disease mainly causes Gill tissue necrosis. Sick eels swim weakly on the surface of the water, sometimes stopping in corners or by the pool where the current is weak. The body color of the diseased eel is slightly dark and there are no obvious symptoms in appearance. If you gently press the Gill with your fingers, red sticky pus will flow out of the Gill hole. Cut off the Gill cover, it can be seen that the Gill filaments begin to fester from the edge, Gill tissue is congested, congestion, and a lot of mucus. The rotten part of the disease is yellow, and there are a lot of sludge debris. In severe cases, most of the Gill filaments rot. The main diagnostic method is to observe the decay and necrosis of Gill tissue. [epidemic and harm] the epidemic season of the disease is long and can be seen all the year round, but it is more serious in the period of high water temperature in summer. It is a common disease, frequently-occurring disease and widespread. Eel farms are popular in Taiwan, Fujian, Jiangsu, Zhejiang and Guangdong. [prevention and treatment] the disease is closely related to high stocking density, insufficient oxygen in water and excess feeding. It has been found that Campylobacter columnar grows well on the surface of eel feed particles, so the spread of residual bait and food will provide favorable conditions for a large number of pathogens per colony. Therefore, to prevent this disease, we should pay special attention to feeding methods, avoid excessive feeding, and often pay attention to the removal of residual bait, keep the water quality clean, increase the number of water trucks, and appropriately increase the amount of water exchange, are all effective prevention and control measures.

There are two kinds of pathogens causing rotten tail of eel: one is Campylobacter columnar, the other is some bacteria of Aeromonas punctata. The cause of rotting tail disease is complicated, which is closely related to eel damage, deterioration of water quality and poor feeding and management in addition to pathogens. [symptoms and diagnosis] the skin of the tail stalk, trunk or head of the diseased fish fester, necrosis and exfoliation. In severe cases, the ulceration goes deep into the muscle layer, and some diseased eels fester at the snout end. The disease is often complicated with water mildew, liver and kidney disease. In the low temperature and rainy season, the festering part is easy to grow water mildew. If the rotten tail continues to develop, it can lead to bacterial septicemia and pathological changes in various organs. The features are: first, the neck is enlarged, but not red; second, there are coagulated blood clots or no blood in the gastrointestinal tract. [epidemic and harm] the disease is a common disease of cultured eel in China, and it is prevalent in different degrees in eel farms in the southeast coastal provinces of China. During the high temperature season in summer, when sorting and other operations cause skin damage and eel sticky flow off, rotting tail disease is most likely to occur. [prevention and treatment] (1) the operation of crossing the pool and selection should be careful to avoid damage to eels as far as possible. When crossing the pond, we should pay attention to the disinfection of fish bodies and ponds to prevent infection. (2) bathing with 4% Mel 5% salt for 1-2 minutes has a good prevention and treatment effect on rotting tail disease.

Red fin disease [pathogen] is Aeromonas hydrophila. The growth temperature range is 5-40 degrees, and the optimum humidity is 8 degrees. It can grow in the range of PH6-11, and the optimum PH value is 7.2-7.4. It can grow in a salt solution with a concentration of no more than 4%, and the optimum salt concentration is 0.5%. [symptoms and diagnosis] the diseased eel initially showed loss of appetite, then wandered away from the group on the surface of the water, leaned against the pool wall or stopped at the bait table. Diseased eel anal fin, pectoral fin, caudal fin and other hyperemia, abdominal or body side skin congestion, red door red and swollen. In severe cases, hemorrhagic plaques can be seen in the abdomen, body side and other parts. Sometimes the skin of the head, trunk and tail will be locally necrotic or infected with water mold. Anatomical observation showed that intestinal congestion and redness could be seen obviously. Pathogenic bacteria multiply in large numbers in the intestinal tract, and the toxins produced first cause intestinal inflammation, and then invade the blood to cause systemic symptoms. When the course of the disease develops to a certain extent, the bacteria invade the blood from the intestinal tract to become septicemia. [epidemic and harm] Red fin disease is a common disease, and there are also fulminant epidemics with serious harm. It is mainly popular in open-air ponds and can be found in eels of all sizes. In spring water temperature rising period, autumn water temperature decreasing period and weather unstable Meiyu period, it is easy to occur and popular, and it is less popular in high water temperature period. [prevention and treatment] (1) every ton of eel was fed with 150-200 grams of sulfamethoxazole or sulfa synergist, and 100 grams per day for 5 days after the second day. (2) every ton of eel was fed with 100 grams of oxytetracycline hydrochloride or tetracycline per day for 5 consecutive days.

Vibrio disease [pathogen] is eel vibriosis. It is a gram-negative Brevibacterium, the growth temperature is 10-35 degrees, the optimum growth temperature is about 25 degrees, and the suitable salt concentration is about 1%. The growth PH value is 6-10, and the suitable growth PH value is about 8. [symptoms and diagnosis] the main symptoms of eel vibrio disease are bleeding and redness of each fin, redness and swelling of the anus, and discoloration, erosion or eminence of the skin of the trunk. Hemorrhagic ulcers appear on the body surface of some diseased fish. The intestines are usually congested. The liver is enlarged and yellowish, with hemorrhagic spots. It is difficult to diagnose eel vibrio disease by observing symptoms alone, and serological methods or pathogen isolation and identification must be used. [epidemic and harm] the occurrence of this disease is the same as red dot disease, which is closely related to the salinity of pond water, and usually does not occur in eels cultured entirely in fresh water. Vibrio anguillarum is a conditional pathogen widely found in coastal water and seafloor. There are certain inducements for the occurrence and prevalence of vibrio disease in eel. Such as the strong stimulation of bad water quality factors, fish body injury and so on. Vibrio anguillarum is mainly carried by seedlings into freshwater eel farms. [prevention and treatment] (1) vaccination of Vibrio anguillarum vaccine. (2) mix oxytetracycline hydrochloride into the feed. Use 100 grams per ton of eel per day for 5 consecutive days.

The red spot disease [pathogen] is Trichoderma anguillarum. It is Gram-negative Brevibacterium, the growth temperature range is 5-30 degrees, the suitable growth temperature is 15-20 degrees, the growth PH range is 5.3-9.7, the suitable growth PH value is 7-9. The bacteria will die in fresh water within a day and can survive in seawater or diluted sea water for more than 200 days. [symptoms and diagnosis] the main symptom of the disease is punctate bleeding on the body surface. Punctate bleeding is the most obvious and most common in the skin of diseased eels, especially in the jaw, abdomen or around the anus. After invading the skin, the pathogens multiply in the epidermal basement membrane and dermis, causing capillary congestion, resulting in exudative bleeding and ruptured plaque bleeding. In addition, fin bleeding, liver congestion, spleen fading and atrophy, kidney atrophy, gastrointestinal and mesenteric punctate bleeding were also seen. The most obvious feature of the disease is that there are many punctate bleeding on the body surface, according to which a diagnosis can be made. [epidemic and harm] the disease occurs in salty eel ponds. The epidemic time is from February to August and from October to November, and the epidemic peak is from April to May. The disease begins to occur when the water temperature is above 10 degrees in early spring, weakens when the water temperature rises to 25 degrees, disappears in midsummer, and spreads again when the water temperature drops below 25 degrees in autumn. [prevention and treatment] Red spot disease occurs at 10-25 degrees. Therefore, in eel culture in greenhouse, controlling the water temperature at 26-27 degrees can prevent the occurrence of the disease. The occurrence of the disease is related to the salt content in the water, so special attention should be paid to eels raised in salty fish ponds. Raising in salt-free fresh water is an important measure to prevent the disease. attention should be paid to changing the pool water used for salt bath and flushing once or twice. The incubation period of the disease is long, the symptoms of the diseased fish have not yet been shown, and the appetite has been lost, so oral drug treatment is difficult to be effective. The furan bath ketone with the final concentration of 2 mg / L can be sprinkled in the whole pool.

Open mouth disease [pathogen] the disease is caused by a virus that lives in the cytoplasm of white blood cells in eels. The virus can be cultured with gonadal cells of eel and can cause cytopathic effect.

[symptoms and diagnosis] cranial hemorrhage, oral mucosal bleeding, head muscle bleeding, lymphocyte infiltration, oral muscle erosion, mouth opening can not be closed, upper and lower jaw congestion, erosion, maxilla shortening, severe mandible fracture, oral cavity completely lost the ability to open and close. When the condition is serious, the liver is congested, enlarged, and even ulcers appear. Diseased fish sometimes show fin congestion. [prevention and treatment] there is no effective method at present

The cause of summer mania in European eel is not clear. It may be due to the inadaptability to the changes of living environment (such as water temperature, light, light quality, food and drug stimulation, etc.), long-term environmental pressure, excessive emergency response of fish, resulting in the imbalance of physiological function of the body. the function of some important organs was damaged and the disease resistance decreased, which eventually led to the death of a large number of European eels. Or it is mainly due to secondary disease or bacterial infection caused by emergency factors, resulting in a large number of deaths of European eel. In order to fully understand the cause of the disease, extensive and in-depth research remains to be carried out. [symptoms and diagnosis] at the initial stage of the disease, a small number of eels swim irregularly at the edge of the pool, swimming weakly, and there are interstitial head twitching, swirling and rolling or backward movement. A few days later, a large number of eels developed similar symptoms with paroxysmal head tremors and died soon after swimming wildly on the surface of the water. The newly dead eel was stiff and its mouth was open. The body surface of the diseased fish is intact, but there are varying degrees of ulcer or congestion in the lower jaw. Some diseased fish have congestion or ulcers in the mouth, anal fins and tail. The Gill filaments of most diseased fish are bright red, the liver is light red, and the kidneys of some diseased fish are enlarged. The red blood cell, hemoglobin and serum chloride ion of diseased eel increased significantly, while the content of blood urea nitrogen and serum cholinesterase decreased significantly. At present, due to the lack of in-depth understanding of the disease, it can only be diagnosed according to the above-mentioned main symptoms. [epidemic and harm] this disease is a serious disease that occurs when European eel is introduced into Asian culture. It is mainly prevalent in the high temperature period in summer, from black eel to adult eel. The disease is so severe that within a week, the mortality rate is as high as more than 90%, and even almost all of them die. [prevention and treatment] there is no effective prevention and treatment at present. Only the following precautions are provided here: 1) do not introduce European eel seedlings in summer to avoid the pressure of high temperature period on new seedlings. It is reported that the water temperature of 20 degrees Celsius is suitable for the growth of European eel, and the continued rise of water temperature from 24 degrees Celsius is very disadvantageous to European eel and should be paid attention to. 2) pay attention to keep the water environment of the eel pond relatively stable and clean to prevent the water quality and water temperature from changing too much. 3) set a shading shed on the eel pond to avoid direct light. 4) the amount of feeding should be controlled during the period of high temperature. 5) pay attention to the timely prevention and control of parasitic diseases and other diseases, fish health can enhance the ability of emergency response. 6) if necessary, use any of the following therapeutic drugs for external use once.