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In recent years, there has been a marked upward trend in silver carp sepsis, sometimes with obvious bleeding symptoms and sometimes without obvious symptoms. Especially after entering the high temperature season in July and August, the incidence rate is high and the mortality rate is large. In addition, the white carp is filter feeding fish, rarely fed feed, in the actual prevention and control process, in general, because of the internal administration of inconvenient operation and unrealistic, mainly rely on external sprinkling drugs to control the disease, therefore, to the treatment of a certain degree of difficulty, treatment is also increasingly difficult.
One. Epidemiological situation and pathogenesis characteristics
Silver carp sepsis, in fact, the incidence of silver carp is higher than that of silver carp, and silver carp rarely occurs, whether this is related to the difference in food habits between the two (silver carp partial phytoplankton diet, silver carp partial zooplankton feeding habits), it is still unknown. Silver carp sepsis is endemic in the spring from March to May and from August to October in autumn, and is most prevalent in august to September in autumn; the incidence is acute, fulminant, and large numbers of dead fish.
(Head congestion)
Although all fish live in the water, the "hydrophilicity" of the silver carp is much stronger, because other fish only rely on the water body to absorb oxygen, but the silver carp not only relies on the water body to absorb oxygen, and the vast majority of its survival food also comes from the water (artificial feeding is a minority after all). Therefore, it may be because silver carp are the main food of plankton in filtered water, when the water quality changes poorly, the pH value is lower than 6.5, which is very easy to cause outbreaks, that is to say, acidic water is one of the root causes of the disease.
Judging from the epidemic situation and prevention results, the high temperature period shows the characteristics of easy recurrence after cure, and the low temperature period shows the characteristics that are difficult to control.
Two. cause of disease
Silver carp sepsis, also known as fulminant haemorrhagic disease, its pathogen is more complex, often the result of a compound infection of viruses and bacteria and even parasites, mostly bacterial infections. This article is based on bacterial properties for an introduction.
(Aeromonas hydrophila)
Common pathogenic bacteria are:
(1) Aeromonas hydrophila. It is susceptible to epidemics in March --- November of each year, and the diseased fish are mainly manifested as systemic bleeding.
(2) Vibrio infection. It is mainly infected by pathogenic strains of Vibrio family, which is susceptible to epidemics from May --- September every year, and the diseased fish are mainly manifested as local bleeding.
(3) Yersinia lucidum . It is susceptible to epidemics in March --- April of each year, and the diseased fish are mainly manifested by local bleeding and spring death.
3. Pathogenic conditions
Pathogen pathogenization depends on the result of interactions between the pathogen, the host, and the aquatic environment. The pathogen of bacterial sepsis is a conditional pathogen, which has the following pathogenic conditions:
(1) Parasitic disease is primary, and bacterial sepsis is secondary.
Whether it is pond culture or reservoirs, lakes and other large water surface culture, the parasitic diseases of silver carp such as ringworms, anchorhead loach, Chinese loach and wheel worm disease are common, the parasitism of parasites not only makes the disease resistance of white carp decrease, but also opens the door to invasion of pathogenic bacteria of bacterial sepsis, such as climate, water quality conditions suitable for the reproduction of pathogenic bacteria, so that the disease can be outbreak.
(2) Poor water quality and substrate cause the outbreak and recurrence of bacterial sepsis.
The causative bacteria of bacterial sepsis are bacteria that naturally exist in freshwater aquaculture. Breeding water body organic matter (residual bait, feces, etc.) is too much, and the bottom mud is too deep, which provides a material basis for the proliferation of pathogenic bacteria with bacterial sepsis, and when the water temperature and other environmental conditions are suitable, it will proliferate in large quantities, which greatly increases the probability of pathogenic bacteria infecting farmed fish. For example, from the perspective of water-loving aeromonas as a primary infection, poor water quality will directly lead to its proliferation, which will cause farmed fish to become infected and cause disease. A large number of facts show that the detection results of ammonia nitrogen and nitrite nitrogen in the cultured water bodies where bacterial sepsis occurs are too high.
(3) Pulling nets (such as catching hot water fish), transport, etc. causing damage to fish function or injury to fish body caused by outbreaks of bacterial sepsis.
(4) Feeding moldy feed, adding water, etc. to cause outbreaks of bacterial sepsis.
Feeding moldy feed is not only toxic to farmed fish, but also changes the intestinal flora of farmed fish, so that the disease resistance of farmed fish decreases and increases the infection rate of pathogenic bacteria; improper water addition, water exchange and flood discharge of large water surfaces will cause farmed fish to produce stress responses, thereby reducing their disease resistance and increasing the infection rate of pathogenic bacteria.
(5) Climatic mutations or frequent changes cause outbreaks of bacterial sepsis.
4. Symptoms
Silver carp populations often have a "dark floating head" phenomenon. At the beginning of the disease, the fish often floats about 10 cm below the surface of the water and swims slowly, reacts sensitively to human shadows, most people are not easy to detect, and when the disease is serious, it is slow or unresponsive, showing a silly performance, multi-day and night (all-weather) floating head, sometimes during the day under the sun's illumination does not sink.
(Gill cap and mandibular congestion)
Visual Inspection:
Freshly dead or dying silverhead carp, the gill cap is rough and mucous on the outside, the gill cap has blood streaks, the submandibular part has strips or scattered erythema, the outer protrusion of the lips is purple, the base of the fin is red, the caudal fin has a white edge without mucus, and in severe cases there are borer fins. The gill cap is cut off, and the gill pieces are red and swollen, the mucus is increased, and the gill silk purple petals are separated in the shape of wooden comb teeth, and there is a blue-white light film on the surface. The reticulated gill rakers are covered with red blood spots, severely off-white and corroded into missing marks.
(Gill filament lobes are separated in the shape of wooden comb teeth)
(Left: hyperemia of the lower jaw and gill cap, right: congestion of the oral cavity)
Dissecting the abdomen of the diseased fish, it can be seen that the color of the gallbladder, liver and kidneys is pale, swollen and fragile; there is no food in the intestine, but it is full of mucus; and the anus is swollen and red.
Primary symptoms
The main symptoms are characterized by body surface bleeding and congestion, especially on both sides of the body surface, head, gill cap, jaw, mouth, fin base, tail stalk, orbit and other parts, some can also see protruding eye and gill silk anemia (white gills); internal organs are also accompanied by different degrees of inflammation, congestion, and some intestines are swollen and inflated. Sometimes presents with asymptomatic features, usually due to acute infection with a strong strain of Aeromonas hydrophila.
Five. Precautions
1. Adjust the water quality: In March to April, the whole pond can be sprinkled with 25 to 40 grams /cubic meter (that is, 30 to 50 kg/mu) of quick ash stone to improve the pH of the water body, because the acidic water body is one of the root causes of sepsis of the white carp.
2. Usual disinfection prevention: dibromohydantoin, chlorine dioxide and other disinfectants can be used for disinfection, the dosage is 0.3 to 0.4 grams / cubic meter, as far as possible once a month in March to September.
3. Insecticidal: Because the sepsis of silver carp is often complicated with parasitic diseases, insecticides can be sprinkled on water bodies, such as inulin, avi, dimethoate, copper sulfate and other insecticides. Or copper sulfate 0.5 g/m3 plus 0.5 g/m3 crystal enemy insects for spilling.
4. Normally open, add aerator: keep the water has enough dissolved oxygen, can inhibit the chemical reaction of toxic substances, conversion or reduce the content of toxic substances (such as ammonia, nitrite and hydrogen sulfide). For example, ammonia and hydrogen sulfide produced by too much organic matter in water (feces, residual bait, carcasses, etc.), under sufficient dissolved oxygen conditions, ammonia will be converted into nitrite and then converted to nitrate; hydrogen sulfide is converted into sulfate, which produces a non-toxic final product and is absorbed by phytoplankton photosynthesis. Therefore, it is very important for aquaculture to maintain sufficient dissolved oxygen in the water. In the absence of oxygen, these toxic substances can easily reach the level of harm quickly. It was determined that when dissolved oxygen in water was increased from 1.54 mg/L to 2.2 mg/L, the content of ammonia or "ammonia" (nh3) was raised from 0.4 mg/l to 0.2 mg/L, and nitrite could be raised from 0.04 mg/l to 0.01 mg/L.
Six. Treatment
1. Use sepsis drugs: apply hemostatic factor drugs such as silver carp outbreak stop, burst hemoping (or burst hemostasis) and other hemostatic factor drugs for whole pool spilling. It is reported that when the fish are seriously ill, after the application of hemostatic factor drugs in the morning, it can be sprinkled with 0.5 to 0.7 g/m3 of copper sulfate in the afternoon to enhance the efficacy. After sprinkling copper sulfate, be sure to pay attention to the activity of the fish to prevent hypoxia.
2. Per mu with bleach powder 1.5 g / m3, salt 1.5 g / m3, urea 0.75 g / m3, enemy insects 0.6 g / m3 tetrax mixture after the whole pond sprinkled, 3 days twice.
3. Per mu with dibromohydantoin 0.25 ~ 0.30 g / cubic meter continuously sprinkled for 2 days, when the disease is more severe, it can be separated for 2 days, and then sprinkled with 0.3 g / cubic meter quaternary amine salt once.
4. When the artificial feeding conditions permit, when feeding powder or granular float, silver carp can be mixed with antipyretic, detoxifying, hemostatic and anti-inflammatory drugs (such as three yellow powder) for feeding. In addition, in the case of helplessness in the diagnosis and treatment of external drugs, according to the characteristics of silver carp, special internal measures can also be used, that is, heat-clearing, detoxification or antibiotic drugs (allowed by the state) are mixed in soy milk and other substances, and then sprinkled on the area where silver carp clusters or downwind outlets are used for silver carp to filter food.
5. For the onset of disease caused by poor water quality, the bottom modified granules are applied to the waters, and the water quality improvement preparations are sprinkled throughout the pond.
6. Root reports that the therapeutic effect of sepsis or hemorrhagic disease of silver carp through octylthion solution is obvious, it is worth mentioning that octylthion itself has no antibacterial effect, so its treatment mechanism is not clear, and even some experts do not believe in its therapeutic efficacy. Common prescriptions are:
(1) Apply 40% octyl thion solution 20 ml / mu + copper sulfate 250 g / mu mixed water sprinkled, which is the most common treatment measure.
(2) Sprinkle octyl thion solution on the first day, and then sprinkle chlorine dioxide on the second day.
(3) 40% octyl thion solution 20 ml / mu + 45% benzalkonium bromide solution 25 ml / mu, mixed water sprinkled everywhere.
The following medications are available:
7. Apply 0.4% avermectin solution 20-25 ml/mu + ferrous sulfate 150 g/mu mixed water sprinkled all over.
8. Apply 50% trichloroisocyanuric acid (strong chlorine) tablets to the whole pool dry sprinkling, 200-300 g / mu.
9. Apply 45% benzalkonium bromide solution per mu of water depth of 1 meter with 30 ml, once a day, continuous use 2 to 3 times.
10. Apply 0.4% ivermectin solution 25-30 ml/mu + ferrous sulfate 150 g/mu mixed water sprinkled all over.
11. Apply 45% dioxide chlorine 200 g/mu + 10% complexed copper solution 300 ml/mu, dissolve and then mix water and sprinkle it over. It is also effective in the treatment of viral silver carp hemorrhage (sepsis).
12. Apply 20% glutaraldehyde solution 25 ml / mu + 10% quaternary ammonium salt complexed iodine solution 150 ml / mu mixed water sprinkled all over.
Fish fulminant sepsis and hemorrhagic diseases can be treated with reference to the contents of this article, this article is for reference only.
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(Note: Most of the pictures in this article come from the Internet, if there is any dissent, it will be deleted)
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