How about koi? diagnosis and treatment of herpesvirus disease of koi

Koi Koi hepesvirus disease virus (KHVD) is an infectious disease caused by herpesvirus (KHV). Current epidemiological studies show that the virus only infects common carp and brocade carp, regardless of fry, juvenile or adult fish, will be infected with KHV, with a mortality rate as high as 80% to 100%.

I. morbidity

In recent years, the incidence of koi herpesvirus disease is high in Guangdong koi culture ponds, and the mortality is high.

Brocade carp culture ponds in Shunde, Nanhai, Zhongshan and Dongguan, Guangdong have all suffered from the disease. The author went to the pond for diagnosis. Received a lot of phone calls about the pond koi rapid onset, a large number of deaths, suspected of koi herpesvirus disease. Many koi enthusiasts bought koi from the market, quickly died, reflecting symptoms, but also systemic bleeding, suspected koi herpesvirus disease. The above examples show the occurrence of a large number of the disease.

Many koi farmers do not recognize the disease and treat it as a common bacterial disease. a large number of koi die, and some areas simply call it "koi plague". They think that there is no cure for this disease. in fact, many koi can be saved and their losses can be recovered. In order to help koi farmers and enthusiasts prevent and better treat the disease and avoid loss, according to the experience in the diagnosis and treatment of koi herpesvirus disease in recent years, write this article to share with you.

Two. characteristics of fish virus diseases

Viruses are very smart. Viruses are chemical and biological. Fish virus diseases have the following characteristics:

1. Pick and choose: when the virus is parasitic on fish, it is very good at choosing hosts, often choosing fast-growing and fat fish as parasites, because fat and big fish are better media than skinny ones. The virus uses the host's enzyme system, energy system, transcription system, etc., to replicate a large number of viruses. A good medium can make the virus replicate more viruses per unit time. After the outbreak of viral disease, often the fat fish die first, leaving small and thin fish, often these fish are still deformed (such as bending of the spine, tail deformities).

two。 Has a strict temperature range: virus disease requires a very high temperature range, the peak of the disease is about 25 ℃, if the water temperature suddenly rises to 35 ℃ and maintains for 24 hours, many diseases may disappear; when the water temperature suddenly drops to 15 ℃ and maintains for 24 hours, many virus symptoms will disappear and the number of deaths will be greatly reduced. The treatment of viral diseases must depend on the weather and pay attention to the weather changes.

3. Virus proliferation organs and effect organs may be different: the virus proliferation organs of fish virus disease are often kidney and spleen, but the effect organs are often skin, liver, etc., the observation of fish virus disease must look at spleen and kidney.

three。 How to simply judge the herpesvirus disease of koi

It should be noted that there is a great relationship between clinical symptoms and the course of disease, in different stages of the disease, the performance of clinical symptoms are different.

a. The incidence is fast, the death rate is large, and the mortality rate is high. The number of fish showing symptoms can rise from 5% to 90% in one day, and the death toll can rise from zero to hundreds in one day.

b. The sick brocade carp floats on the surface, some floats on the surface, some lie on the side of the water; the sick koi shows mental depression and loss of appetite; swimming with no sense of direction occurs in behavior, or floats upright on the head and tail in the water, or even stops swimming; if you get sick in the cement pool, you will find many koi lying on the side at the bottom of the water, especially in the inlet and outlet, and some farmers call it "drowsiness".

c. The diseased carp had bleeding on the body surface and local ulcers; the scales were loose, the scales fell off, and blood filaments appeared on the scales.

d. Brocade carp Gill cover bleeding, open Gill cover, Gill silk color dark red, Gill wire bleeding, tissue necrosis, Gill wire end necrosis and whitening.

e. The fin, especially the caudal fin, is severely congested, partially bleeding and seems to be covered with white mucus.

f. Red and swollen anus

g. Tear open the skin, there are symptoms of subcutaneous congestion and muscle bleeding, bleeding and congestion are more distributed along the muscle thorns; because there is part of red meat under the skin of carp, attention should be paid to the difference between red meat and muscle bleeding.

h. Open the abdominal cavity, the blood clots quickly, the outflow of blood is obviously less and coagulates very quickly, about 6 seconds to start rapid coagulation, blood coagulation time is obviously shorter than healthy fish; cut the heart, bleeding is significantly less than healthy carp, and rapid clotting

i. The intestinal tract has no catarrhal inflammation, but the intestinal tract is congested and red, and the intestinal tract is stiff and red, indicating that it is not a bacterial infection.

j. Cholecyknosis and darker bile of the diseased koi

k. The liver of the diseased koi has small bleeding spots at the edge of the hepatic lobule, the surfactant is reduced, and the liver is fragile.

l. There are bleeding spots in the spleen, and microscopic examination shows that there are a few bleeding spots inside, and the bleeding spots are bright red.

m. The posterior kidney is enlarged, microscopic examination has bleeding spot, bright red.

Farmers often reflect: a, b, c and e of the fish lethargy, body surface bleeding, tail bleeding, other symptoms need to be grasped by fish disease prevention and control personnel.

Four. disease analysis

Koi herpesvirus is a kind of virus with strong pathogenicity and high fatality. it shows the characteristics of rapid onset, high infection rate and high mortality. After the koi is infected with the virus, the virus destroys the nervous system of the fish, resulting in decreased activity, imbalance of balance and lethargy. The disease occurs quickly, does great harm to the koi, and is unbearable to the koi. It is easy to scratch the skin, coupled with microvascular rupture, showing the symptoms of skin bleeding, resulting in massive microvascular bleeding, resulting in the collapse of the blood coagulation system of koi, causing multiple bleeding in the body. Multiple organ failure and death.

Five. time of onset

It is reported that the optimum culture temperature of the virus in the laboratory is 21 ℃, the onset water temperature is 18-29 ℃, and the peak water temperature is 22-28 ℃. The disease often occurs in spring and autumn, and generally occurs in late April and early September in Guangdong. However, the weather in 2008 and 2009 is quite abnormal, and it has entered a period of climate chaos. In 2009, some ponds became ill in late October and November, making it more difficult to prevent and control.

VI. Prevention and control

6.1 Prevention

6.1.1 Prevention begins one month before the disease-prone period, that is, prevention begins in March and August; specific measures: administration of appropriate drugs (40 kg feed: "hemostatic fast" 3 packets + "Like 101" 1 package + "florfenicol" 1 package + internal medicine synergist 1 package), improve fish immunity and increase the content of fish coagulation factors Sprinkle "excellent iodine" (1 mu for 1 bottle) or "polyiodine" (2 mu for 1 bottle) every 5 days.

6.1.2 reduce the stocking and breeding density of common carp, reduce the yield per unit area, and stop strong stimulating activities such as net-pulling in the disease-prone period.

6.1.3 do not introduce other koi during the onset period. In November 2009, a farmer in the South China Sea bought koi and put it in a cement pond. The water flowed into the koi pond. The next day, the koi pond got sick and died a lot.

6.1.4 do not turn over the bottom of the pond during the disease-prone period. In 2008, a brocade carp culture pond in Shunde was prevented according to the scheme we provided, and there was no disease. However, in 2009, it was still carried out in accordance with the plan, and one of the ponds suddenly fell ill. The author rushed to find that it was the farming owners who fished up the sediment to make lump flower fertilizer and turned over the bottom of the pond, resulting in the deterioration of water quality and the emergence of a large number of viruses.

6.1.5 vehicles and personnel entering the site are disinfected with "superior iodine". The production appliances of each pond should not be mixed, and disinfectants are often used for disinfection; in the early stage of the disease, high concentrations of "superior iodine" are regularly sprinkled on the ridge of the pond to reduce the possibility of virus transmission.

6.1.6 choose suitable feed, 10 days before the peak of the disease, reduce the amount of feed to 40% of the usual amount of feed.

6.1.7 during the disease-prone period, the activities of fish were observed frequently every day, and several carps were sampled every day for detailed observation.

6.2 treatment

6.2.1 confirm that it is the disease

Judge whether the disease is caused by epidemiology and the characteristics of the disease, and send the suspected cases to the relevant personnel for diagnosis immediately.

6.2.2 No indiscriminate use of drugs

Do not drug casually, when the outbreak of viral disease taboo random drug, often have the opposite effect.

6.2.3 treatment regimen

Turn on the aerator, ① to reduce the amount of feeding, oral administration: appropriate drugs (40 kg feed: "hemostatic fast" 3 packets + "Like 101" 1 pack + "florfenicol" 1 package + internal medicine synergist), improve fish immunity and improve fish blood coagulation factor content; ② sprinkle: use "Bishuishuang" (1 bottle of 1 mu water surface) throughout the pond for 3 days Sprinkle with "clean water treasure" (1 pack of 1 meter 1 mu of water surface) in the whole pool for 3 days, and disinfect it with "excellent iodine" (2 bottles with 1 mu) on the 3rd and 5th day. This scheme has a better therapeutic effect, but it requires farmers to communicate with relevant personnel according to the actual situation.

If there are parasites such as ring worms in the gills, you can't kill them at this time. If the water has turned white, it needs to be reflected to the relevant personnel.

6.2.4 Disinfection environment

Strictly control the entry and exit of personnel, vehicles and appliances; do a good job in disinfection of personnel and tools in the breeding area, disinfect with "superior iodine"; sprinkle with high concentration of "superior iodine" on the ridge of the pond many times a day to prevent the spread of pathogens.

6.2.5 look at the weather

In the next 2 days after the onset of the disease, the temperature will change sharply more than 12 ℃. Congratulations, the fish will be fine if you don't save the fish. In November 2009, koi fell ill in a culture pond in Shunde, and 300 koi died every day in a pond of 3 mu. I paid attention to the weather. When the cold wave in the north came, the temperature dropped more than 15 ℃. I asked the farmers to use "clear water cool", and let it use "excellent iodine" on the third day, telling him that it would be all right in 4 days. Guangzhou began to cool down the next afternoon, and on the fourth day, only three fish died, and there was no further death within a month.

However, relying solely on weather treatment, if the water temperature rises again to the virus-prone water temperature within 1 month, the koi is easy to break out herpes virus disease again after about 1 month.

6.2.6 variation of water temperature

Koi raised in small water bodies in the family can be treated by changing the water temperature. Put the sick koi in an aquarium and slowly raise the water temperature to above 33 ℃ for 24 hours, or put the diseased fish in an aquarium and lower the water temperature to about 15 ℃ with ice for 24 hours. The disadvantages of this method are: ① household users do not have a good grasp of heating and cooling, resulting in greater stress death of fish; ② is easy to relapse again one month later.

What needs to be reminded is that the fish after the change of water temperature should be taken orally in time: appropriate drugs (40kg feed: "hemostatic fast" 3 packets + "Like 101" 1 package + florfenicol 1 package + internal medicine synergist). Improve fish immunity and increase the content of blood coagulation factors. Practice has proved that changing water temperature + improving fish immunity and increasing the content of coagulation factors can prevent fish from relapse after one month.

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