Common diseases and prevention of protocephalus crawfish
Shrimp diseases occur as a result of the interaction of pathogens, environmental factors and shrimp. As a benthic aquatic animal, crayfish most of the time inhabit the bottom of the water, grass and caves, and are usually difficult to meet in water bodies, and even if they encounter them, they will quickly escape. Therefore, when patrolling the field (special weather exceptions), it is found that the water quality is suddenly changed, the crayfish are lying on the shore, climbing on the grass, the response is slow, the food intake is reduced, and individual deaths are found, indicating that the crayfish have signs of disease or have become ill.
The disease research of crayfish is shorter than the history of artificial breeding, and many problems are not fully understood at present, so the treatment of shrimp diseases should be based on the sixteen-character policy of "disease-free prevention, early treatment of diseases, prevention as the mainstay, and combination of prevention and control". Here, we summarize the diseases that occur across the country and the diseases in the relevant literature to help farmers better treat the diseases of crayfish. Common diseases of crayfish can be divided into viral diseases, bacterial diseases, fungal diseases and parasitic diseases.
1. Viral diseases
The most reported viral disease in crayfish is leukoplakia syndrome. The pathogen is leukoplakia syndrome virus, a baculovirus with a capsular membrane.
Leukoplakia syndrome is one of the common diseases in crayfish rice farming, also known as the "May Curse", which has been widely prevalent in recent years, seriously harmful and has a high mortality rate. Specialized in dead prawns, small shrimp have little impact.
[Symptom characteristics l Hyperesphoria at the beginning of the disease, the amount of food intake is significantly increased.] For about 3 days, the shrimp's feeding intake decreased, their activities weakened, their response was sluggish, and some of them lay quietly on the aquatic grasses by the pool, and their body color was dark. Anatomy can see that the diseased crayfish has dirty abdomen, the cephalothorax and abdominal carapace are easily peeled off, the inner layer has a soft carapace, there is a fluid accumulation in the body, the liver and pancreas are enlarged and the color becomes lighter, the gills are black, the gastrointestinal tract is empty and foodless, the color is green, there is obvious intestinal mucosal bleeding and edema, and the hemolymph is not easy to coagulate (Figure 0). Adult shrimp morbidity is the highest, and shrimp fry disease is rare.
Figure 0 Comprehensive evidence of leukoplakia
[Epidemiological characteristics] The incidence of water temperature is 18 - 25 °C, the peak of the epidemic from mid-April to May, and the mortality rate is more than 90%.
[Preventive measures] Prevention is the mainstay, prevention and control are combined. Prevention mainly starts from the early market, rational arrangement of breeding density, maintaining a good breeding environment for water bodies and substrates, and improving the immunity of crayfish. 1) Increase the dissolved oxygen of the water body; 2) Enhance the immunity of the crayfish body; 3) Disinfect the water body regularly; 4) Increase the amount of heat, detoxification, liver protection and liver protection drugs; 5) Change the water after 24 hours and the water source is good; 6) After taking the drug, the crayfish can be transferred to the pond when the vitality is better to reduce the breeding density; 7) Early seeding, early harvest; 8) Crayfish after the cage fishing, should not be put back into the field, because it is easy to activate the leukoplakia syndrome virus.
[Treatment] At present, there is no specific drug for this disease. After the onset of the disease, stop eating and changing water, fish out dead shrimp and bury them deeply to avoid fulminant infection, and disinfect the utensils. Strongly irritating drugs should not be used when a viral disease is diagnosed, and feeding activities should be carried out in order to avoid stress in crayfish.
2. Bacterial diseases
From the existing farming process, it is found that April to June of each year is the high incidence period of crayfish disease, during which the disease caused by pathogenic bacteria in bacterial conditions is a more prominent multi-faceted common disease at this stage. The number of deaths in the initial stage of the disease is small, the number of deaths increases with the change of time, and the complications further caused by the onset of the disease are becoming more and more urgent, the epidemic is getting faster and faster, and the losses caused are also getting larger, which brings greater difficulties to the prevention and control of breeding and diseases. For example, diseased shrimp will often have symptoms of claw weakness, rotten gills, rotten tails, dark spots on the carapace, and ulcerated edges.
Common pathogenic bacteria that cause bacterial diseases in crayfish include: Freundii citicidum, Vibrio parahaemolyticus, and Aeromonas hydrophila. Because these pathogenic bacteria are present in the water body all year round, they will only multiply in large quantities if the water quality deteriorates or there is more silt at the bottom of the pond, and the bacteria need to reach a certain number of pathogens to cause the disease. The main control techniques of several common bacterial diseases are introduced for the reference of farmers.
1． Carapace ulcer disease
[Symptom characteristic 1 The disease is caused by a bacterial infection of chitin decomposition.] In the initial stage, dark spots appear in the carapace of the diseased shrimp, and then the edges of the spots ulcerate and appear hollow, and gradually develop into a lump as the lesion worsens, and the muscles under the center of the mass are ulcerated, the edges are black, and they will die over time (Figure 1).
Fig. 1 Crayfish carapace ulcer disease
[Epidemic characteristics] occur everywhere, and the main epidemic period is from May to August. All crayfish can be infected.
[Preventive measures] Try to make the shrimp body free or less traumatized, improve water quality conditions, carefully manage, feed, and provide sufficient concealment. When operating in the breeding link, the action should be gentle to minimize damage, and when transporting and stocking shrimp fry and shrimp seeds, do not pile up and damage the shrimp body. Control the stocking density of crayfish seedlings and achieve reasonable intensive culture. Keep the water fresh, oxygen sufficient and feed fresh. The water body is disinfected with chlorine dioxide (or strong chlorine, bleach, etc.) and fed medicinal bait for 10-14 days.
[Treatment] Sprinkle the whole pool with 15 - 20 grams of tea meal soaking solution per cubic body of water. Sprinkling with 5-6 kg of quicklime per acre, or 2-3 grams of bleaching powder per cubic body of water, can also play a better therapeutic effect, but quicklime and bleach powder can not be used at the same time.
2． Gill rot disease
[Symptom characteristics] Due to a large number of Vibrio and other bacilli parasitizing on the gills of the diseased shrimp, through a large number of reproductions, the blood in the rich capillaries of the gills cannot circulate, resulting in a decrease in oxygen content, preventing the respiratory function of the shrimp, and making the growth of the diseased shrimp slow; the gill filament will lead to blackening, mildew, atrophy and necrosis of the gill tissue due to lack of oxygen for a long time, and death due to lack of oxygen. Shrimp with the disease usually surface or cling to aquatic grasses out of the water, in severe cases of infection, the growth of filamentous bacteria can be found above the shrimp's swimming foot and carapace, and after infection, the diseased shrimp will appear slow, abnormal, sluggish and decreased feeding.
[Epidemiological characteristics] from juvenile shrimp to adult shrimp can be infected, this disease generally occurs at a temperature of more than 15 ° C, the water temperature began to prevail in the range of 15 - 30 ° C, and the higher the temperature, the easier to spread. The disease is caused by the direct contact of the pathogenic bacteria with the shrimp body, resulting in direct infection, such as after the gills are subjected to external force and mechanical damage, the pathogenic bacteria are more likely to infect the shrimp body.
[Preventive measures] Before releasing seedlings, use quicklime and other thoroughly clear the pond; follow the "four certainties" principle of feed feeding, that is, timing, quantification, positioning, and quality, often remove the residual bait and dirt in the rice field, timely fill with new water, ensure the high-quality water environment, maintain the environmental health and safety of aquaculture, so that the dissolved oxygen in the water body is often maintained at more than 5 mg / liter, to avoid water quality pollution,
[Treatment method] with chlorine-containing disinfectant (such as bleach powder, etc.) 1.5 g / m3 in the whole pond within the breeding range, because the chlorine-containing disinfectant can interact with the bacterial plaster protein in the bacteria, produce oxidation reaction and chlorination reaction, and present a disinfection and sterilization effect, can play a better therapeutic effect, but it should be emphasized that quicklime and bleach powder can not be used at the same time. When the water is disinfected, it can be fed with mixed feed such as allicin, 2 times a day, and used for 5-7 days.
3． Rotten tail disease
[Symptom characteristics] Caused by a large number of bacterial pathogenic infections or chitin-loving decomposition bacteria caused by bacterial infection, shrimp body due to external factors (such as manual operation or mechanical damage such as fishing and stocking, transportation and so on) so that a large number of pathogenic bacteria parasitize at the tail end, the diseased shrimp is slow to respond, and the grass is powerless on the shore. At the beginning of infection, part of the tail fan is red and swollen, there are small sores, containing liquid, with the deterioration of the condition, it is easy to cause tail defects and blackening for a long time, and from the edge of corrosion erosion to the middle of the development, when the serious infection of the entire tail will be swallowed, sometimes also show the phenomenon of broken whiskers, broken feet and so on.
[Epidemiological characteristics] The disease is a common disease of shrimp, when the shrimp is mechanically damaged, it will increase the infection rate, the epidemic water temperature is above 12 °C, and the infection rate increases with the increase of water temperature, which has the characteristics of fast infection speed and wide spread. When such diseases occur, it is necessary to isolate the farmed diseased shrimp, disinfect in time, control the water temperature, keep the spread of the disease within a controllable range, and avoid greater losses.
[Preventive measures 1 Usually pay attention to maintaining good aquaculture water quality, regular disinfection, regular water replacement, the disease should be thoroughly disinfected in the whole field. In the process of transportation, transfer culture and handling, attention should be paid to avoiding damage to the shrimp, and the cage should be selected on a sunny day to control the stocking density.
[Treatment method] When the disease occurs, 15 - 20 g / m 3 tea meal soaking liquid can be sprinkled in the whole pool, or the tea meal residue can be placed around the cultivated rice field by hanging bag hanging basket method, and the tea meal residue can be automatically soaked. Sprinkle with bleach or chlorine-containing disinfectant to achieve a better therapeutic effect. When the disease is cured, the use of quicklime and photosynthetic bacteria and other microecological preparations cross-rotated whole tank sprinkling, use once a half a month, which can effectively adjust the pH of the water body, to achieve the effect of improving the water body, reducing the ammonia nitrogen content and other chemical components in the pool.
3. Fungal diseases
It mainly includes black gill disease and water mold disease.
1. Black gill disease
[Symptoms and features] The gills change from flesh color to brown or dark brown until they become black, and the gill tissue atrophies and necrotic. The diseased juveniles are weak in activity, and most of them crawl slowly and stop eating at the bottom of the pool. Diseased adult shrimp often surface or cling to aquatic grasses to expose themselves, do not enter the cave, move slowly, and finally die of breathing difficulties.
[Epidemic characteristics] After continuous rain or heavy rainstorms, due to the shallow and turbid water, water pollution and insufficient light can easily cause mold infection.
[Preventive measures] Change water frequently, remove residual bait and spoilage in time, and regularly disinfect water bodies with quicklime or chlorine dioxide.
[Treatment] Sprinkle with bleach powder in the whole tank, 1 time a day, 2-3 times a day, or use povidone iodine to sprinkle disinfection.
2． Water mold disease
[Symptom characteristics] The initial symptoms are not obvious, when the symptoms are obvious, the hyphae have invaded the epidermal muscles, and the water is grayish white, like cotton flocculent. The muscle tissue at the wound is covered with hyphae of varying lengths, and the tissue cells in this area gradually necrosis. Sick shrimp are emaciated and weak, anxious, reduced feeding, and in severe cases, death.
[Prevalence] occurs more often in 18 - 21 ° C.
[Preventive measures] When the water temperature rises to more than 15 ° C, sprinkle the whole pond with quicklime water, and thoroughly disinfect the stocked rice field; in the fishing and handling, careful and careful should be taken to avoid shrimp damage and sticking to the silt; avoid rain and snow to avoid frostbite; wintering or stocking water bodies must be cleaned and disinfected to kill predators, parasites and pathogens to reduce the chance of water mold invasion.
[Treatment method] Use table salt and baking soda to mix the whole pool, once a day, for 2 days, if the effect is not obvious, change the water and then take the drug for 1-2 days. Sprinkle 1-2 times with a whole tank of chlorine dioxide, and the interval between the two doses should be 36 hours.
4. Parasitic diseases
It is mainly protozoa and ciliate. Ciliate disease is one of the common diseases in crayfish rice field farming, and it is very harmful, and the disease has been reported throughout the country.
[Symptom characteristics] Crayfish shrimp with ciliary disease have many brown or yellow-green villi on the surface, appendages, gills and other parts, no sensitive response to external stimuli, weak activity, emaciated shrimp body, blackened head and breast nails, mucus on the surface of the shrimp body, the whole body is covered with mud dirt, and drag strips, commonly known as "dragging mud disease" (Figure 2).
(Figure 2.)
[Epidemiological features] Adult shrimp, juvenile shrimp and fertilized eggs are susceptible to infection and are very susceptible to occurrence in water with a lot of organic matter. The disease can occur throughout the country.
[Preventive measures] Thoroughly disinfect with drugs to keep the water clean; during the production season, replace the new water once a week to keep the pond water fresh; when shrimp species are stocked, shrimp seeds can be soaked in salt water for 3-5 minutes. For marketed crayfish, the surface of the shrimp can be rinsed with groundwater for 2 days, and the ciliates will fall off on their own if they lose their nutrient supply.
[Treatment 3 Soak diseased shrimp with a combination of 0.5 to 1 g/L neo-g/L potassium permanganate; sprinkle whole tank with 0.7 mg/L copper sulfate and ferrous sulfate (5:2) mixture; soak the diseased crayfish in a solution of acetic acid, and most of the solid ciliates are killed.
5. Other types of diseases
1. Soft shell disease
[Symptoms and characteristics] The disease is due to insufficient light, long-term low pH, too thick silt at the bottom of the pond, excessive density of shrimp fry, long-term feeding of single feed, and difficulty in calcium and phosphorus conversion after the vege shell, resulting in the inability of the shrimp body to use calcium and phosphorus. The shells of the sick shrimp become soft and thin, the body color is not red or gray, the activity is poor, the foraging is not exuberant, the growth rate is slow, and the coordination ability of various parts of the body is poor.
[Epidemiological features] juvenile shrimp are susceptible to infection.
[Preventive measures] Dredging and exposure in winter; thoroughly clearing the pond with quicklime, sprinkling with 20 mg/l of quicklime water every 20 days after the release of seedlings; control of stocking density; diversification of feeding, appropriate increase of calcium-containing feed.
[Treatment] When the water quality is poor, the water should be changed in large quantities to improve the water quality. When the disease occurs, it is sprinkled with 25 mg/l of quicklime water per month in a whole pond; fresh okara or other feed is fed with fish bone meal once a day for 7-10 days; and the whole pond is sprinkled with Bacillus subtilis 0 every half a month. 25 g/m3; Add 3% -5% metasin to the feed and feed continuously for 5-7 days.
2． The molting does not succeed
[Symptom characteristics] The diseased shrimp has a crack at the junction of its head and chest and abdomen, and its whole body is blackened.
[Popular characteristics] often due to the lack of a certain element of the growing water body, weather changes are also easy to lead to the failure of the tap shell. Shrimp of all sizes can occur, especially juvenile shrimp.
[Precautions] Sprinkle every 15 -20 days with whole tanks of quicklime water; monthly sprinkle with whole tanks of calcified water per phosphate.
[Treatment method] 1% 0-2% 0 metamorphosis in the feed; bone meal, eggshell powder and so on are mixed in the feed to increase calcium.
3． Pan pool
[Symptoms] When the crayfish are lacking oxygen, they are restless, sometimes crawling into the grass on the shore in groups, and some climbing ashore, if they leave the water body for a long time, it will lead to death.
[Epidemic characteristics 3 Can occur in all seasons, mainly due to lack of oxygen in the water body. ]
[Preventive measures] During the winter leisure period, it is necessary to remove too much silt in time and freeze the bottom of the pond; use fermented organic fertilizer to control the water quality is too thick; control the stocking density of shrimp species; often add new water to keep the water body fresh.
[Treatment] If the shrimp is found to be uneasy, it should be filled with new water, but it cannot be directly flushed in, it is best to spray into the water surface; if the water quality is turbid, sprinkle the whole pond with 2-3 kg of alum per acre; other oxygenation measures can also be used.
Diseases in the process of breeding crayfish will cause great losses, as long as we adhere to the healthy breeding idea of prevention over treatment, disease-free prevention, early treatment of diseases, regular disinfection, improve water quality, timely removal of dead shrimp, control of bacteria, viruses and other reproduction quantities, we can scientifically and effectively prevent diseases. In the production process, disinfectant drugs are used in rotation as much as possible to avoid drug resistance, so as to achieve effective disease prevention. Freshwater crayfish disease species and pathogens are more, farmers in the breeding process will often encounter a series of diseases and problems, in the field selection of diseased shrimp sampling diagnosis, in addition to the fixed ciliates (such as polyconders, monofidocysts, etc.) can be directly through the naked eye observation to confirm the diagnosis, diseases caused by viruses, such as leukoplakia virus disease, bacterial fungus caused by diseases are not easy to diagnose, must be analyzed and diagnosed through the laboratory, but through the epidemic law can be the initial judgment of the disease, so usually to strictly grasp the prevention and control of diseases, early prevention, Pay attention to disinfection, strengthen the training and daily management of breeders, and establish a high awareness of prevention and control, so as to achieve better and faster development of the crayfish farming industry.