Prevention and treatment of fulminant hemorrhagic disease of silver carp in Shantang Reservoir

From August to September in 2005, a large area of fulminant hemorrhagic disease of silver carp occurred continuously in Baiyuan Reservoir, Shachong Reservoir and other small reservoirs in Pingle County, Guangxi, with an area of about 590mu. The fish died within two days with 5386kg and 600~1000g/, and the economic loss reached more than 20, 000 yuan. The disease is ferocious, the mortality rate is high, and the disease is easy to repeat and difficult to control, so it should be paid great attention to by the majority of fishery farmers.

1 epidemic situation and characteristics of the disease

The epidemic season is from March to May in spring and from August to October in autumn, and the most popular is from August to September in Autumn. The disease is characterized by acute, fulminant, and mass dead fish. If treatment is not taken in time, the mortality rate is 80%, 90%, or even 100%, within 3-5 days of the disease. When the water quality changes badly and the pH value is lower than 6.5, it is easy to cause outbreaks and epidemics, and in the waters where the disease has occurred, silver carp culture is also easy to relapse in the second year.

2 water quality environment

The water quality is thin, the water color is gray, the transparency is above 30cm, and the pH value is between 6 and 7. There are few phytoplankton, more organic detritus and more zooplankton in the water, among which rotifer is dominant.

3 symptoms

The phenomenon of "dark floating head" often occurs. In the early stage of the disease, silver carp often float under the water and swim slowly and respond sensitively to human shadows, but when the disease is serious, they are slow or unresponsive, showing Muna, floating their heads day and night, and the sun does not sink during the day.

Appearance examination: freshly dead or dying silver carp, the Gill cover is rough without mucous membrane, there is blood in the inner part of the operculum, there are strips or dotted erythema in the lower jaw, the lips protrude purple, the base of the anal fin is red, the caudal fin has white edges without mucus, and serious fin decay. When the Gill cover bone was cut off, the Gill piece was red and swollen, the mucus increased, the Gill filament black and purple petal separated in the shape of a comb, and there was a blue-white light film on the surface. The reticulated Gill rake is covered with red blood spots, which is grayish white and corroded into notches. Dissecting the abdomen of diseased fish, it can be seen that the color of gallbladder, liver and kidney becomes lighter, swollen and fragile; there is no food in the intestine, but it is full of mucus; the anus is swollen and swollen.

Microscopic examination: there was a white film on the outside of the Gill filament, with wave-like spores, red and swollen ends of Gill patches, blood sinuses, and a large number of monosporidium microsporidia after being crushed. There is a large amount of water in the abdominal cavity and there is hemolysis.

4 Preventive measures

Clean up and disinfect thoroughly. After fishing in winter, remove too much silt from the bottom of the reservoir and expose it to the sun. From March to April before the rainy season, the limestone 25~40g/ cubic meter can be used to sprinkle the whole pool while the water level of the reservoir is low and the water body is small. For the reservoir where the disease has occurred, it is best to thoroughly disinfect the reservoir with dibromohydantoin, chlorine dioxide and other powerful disinfectants after 7 days, the dosage is all 0.3~0.4g/ cubic meters.

Choose strong and neat fish species for stocking. Fish are bathed with 2%-3% salt water or 15~20g/ cubic meters of potassium permanganate before entering the pond. 10~15min.

During the fish disease epidemic season, regularly sprinkle the whole pool with 20~30g/ cubic meters of quicklime, dibromohydantoin or trichloroisocyanuric acid 0.3~0.4g/ cubic meters. As the fulminant hemorrhagic disease of silver carp often occurs with parasitic diseases, it is necessary to sprinkle the whole pool with Shuangxiaoling 0.03g/ cubic meters plus copper sulfate 0.3~0.4g/ cubic meters or copper sulfate cubic meters plus 0.5g/ cubic meters of crystal trichlorfon before the end of April every year.

5 methods of treatment

The whole pool was sprinkled with 20~25mg/ mu, then the whole pool was sprinkled with copper sulfate 0.4~0.5g/ cubic meters half an hour later, and the next day it was sprinkled with the whole pool to strengthen the curative effect.

Sprinkle every mu with bleach 1.5g/ cubic meters, salt 1.5g/ cubic meters, urea 0.75g/ cubic meters, trichlorfon 0.6g/ cubic meters mixed and sprinkled in the whole pool, twice in 3 days.

0.25~0.30g/ cubic meter of dibromohydantoin was sprayed continuously for 2 days per mu. When the disease was serious, the interval was 2 days, and then sprinkled with 0.3g/ cubic meter Qiangke 101 (superiodinated quaternary amine salt) once.

6 points for attention

The volume of reservoir water should be calculated accurately when using drugs. If the error is less than 10%, the reservoir capacity can be determined according to the reservoir elevation and capacity curve (table).

The method of medication should be scientific. The amount of disinfectant for external use can be adjusted according to the fat and thin water quality and the water temperature, but it must not exceed 20% of the conventional dosage; when it is applied, it must be sprinkled evenly, and more drugs should be used in deep water areas, so as to ensure the effect of drug use and prevent drug damage caused by improper use of drugs. avoid the occurrence of dead fish accidents. After sprinkling copper sulfate, we should also pay attention to observe the activity of fish to prevent hypoxia.