【 Symptoms 】 The crustacean on the body surface of the diseased shrimp has spotted black-brown ulcer, with a concave middle and a white edge. Brown spots vary in size and can occur in all parts of shrimp, especially in the back of the head, chest and the first three sections of abdomen. Appendages such as tentacles and tail fans sometimes have brown spots and rotten breaks, and the broken marks are also dark brown. When the disease is serious, the lower crust tissue is also eroded, and the destruction of the crust causes the balance of osmotic pressure. Adhesion between the old and new crustaceans leads to difficulty in molting and death. Bacteria that cause crustacean ulcers will not penetrate into the tissues below crustaceans, but it can increase the chances of other bacteria invading. In addition, the shell also affects the beauty of shrimp, which leads to the decrease of commodity value.
【 Etiology 】 The etiology of this disease is the result of the joint action of several bacteria and algae that can produce various lipases, proteases and chitinase, and may be accompanied by secondary infection of bacteria and filamentous bacteria. The bacteria detected on the brown spot of diseased shrimp include endophyte, Vibrio, Pseudomonas, Aeromonas, myxobacteria, etc., but these bacteria all have the ability to decompose chitin. But none of the artificial infection tests were successful. Therefore, it is speculated that brown spots are caused by other reasons, such as scratching the surface of shrimp during fishing and transportation, or suddenly turning into a polluted environment, malnutrition and so on. It will also cause the destruction of the skin of the parent shrimp and cause diseases.
[Epidemic Situation] The disease is widely distributed in the world. The pathogen is crustacean corrosive bacteria. It is ubiquitous in seawater, fresh water and salt water, and is a normal part of the bacterial flora of living or dead crustaceans. The number of bacteria changes with the change of environment. Shrimp cultured in harsh environment was quickly infected, and the infection rate reached 100%. After changing environmental conditions, thinning stocking density, raising water temperature and feeding high-quality feed containing antibiotics, some critically ill patients were soaked in formalin (70 mg/kg). The results were almost 100%, and the critical condition was relieved, and the molting was cured several times.
[Prevention method] First of all, don't get hurt; In addition, it is necessary to improve feeding conditions, carefully manage daily life, rationally distribute feed, and provide enough accessories and shelters. In order to improve water quality, drugs are generally discouraged, except bacteria.
〕 Treatment 〕 ① Oxytetracycline 0.45g was mixed with 1kg feed for 2 weeks. ② Take 20 ~ 30mg/kg tea residue 1 day, and then change water to raise the water temperature to promote molting.
(2) At the initial stage of infection, the tail fan of the diseased shrimp has blisters (swelling filled with liquid), which leads to the edge of the tail fan festering, necrosis and incompleteness; In severe cases, the whole tail fan was swallowed, and it was also characterized by broken whiskers and black spots on the body surface. This disease is common in overwintering parent shrimp ponds.
【 Etiology 】 ① Chitinolytic bacteria infection. ② Shrimp is injured by extreme stimulation (such as bouncing). ③ It is caused by cannibalism when molting.
(Treatment) ① Soak the tea residue for 6 hours and sprinkle it into the whole pond at the ratio of 15 ~ 20mg/kg. (2) 5 ~ 6 kg/mu of quicklime overflowed the whole pond.
(3) white shrimp disease (white syndrome)
【 Symptoms 】 The disease mostly occurs shortly after the parent shrimps selected from the culture pond enter the wintering pond (about 10 ~ 20 days). At first, only the head and breastplate turned white, then the white part gradually spread to the whole head and breastplate, the epidermis lost its pigment, the shell gradually softened, and the middle thymus shrank. This disease is mostly caused by female shrimp. The longer the bleaching time of shrimp, the harder it is for parent shrimp to shell. Therefore, it is difficult for immature shrimp to mate and molt again. The disease is not obviously contagious, but the mortality rate is higher than that of normal shrimp, and the surviving individuals can lay eggs and hatch normally.
【 Etiology 】 Adult shrimps fed with artificial feed in ponds (overwintering ponds) that cannot be exposed to direct sunlight are prone to this disease. It may be due to the atrophy of epidermal pigment cells and the continuous loss of pigment. Putting shrimp into the pond during transportation is a general physiological protection reaction caused by mechanical collision or environmental mutation.
[Prevention and control methods]
① When selecting parent shrimp ponds for operation, we should be extra careful, and the environmental changes should not be too great. In the management of parent shrimp wintering period, we should also prevent diseases caused by improper operation. ② Isolation of diseased shrimps, strengthening culture, raising water temperature, and promoting parent shrimps to shell. ③ Feeding high-quality feed to improve the culture environment.
(4) molting disorder [disease] This disease mainly appears in the late larval stage and the young shrimp stage. Death occurs when you shed your skin during transformation. Because the head and chest appendages and frontal angle can't fall off, most larvae die in the old shell; Some larvae die immediately after molting. After molting, the appendage is deformed and the shell sinks. The mortality rate of larvae of this disease can reach 20% ~ 30%, and the sediment of this shell is found in the molting shell. The analysis results show that the deposit is calcium-containing substance precipitation, and the amount of calcium precipitation is positively correlated with the sinking amount of the shell.
【 Etiology 】 Artemia in different areas, malnutrition, poor water quality and calcium deposition on the exoskeleton shell are all the causes of this disease.
【 Control method 】 Supplementing green water (phytoplankton), increasing nutrition, improving water quality and adding appropriate larval feed such as lecithin and tofu.
(5) Muscle white turbidity (muscle necrosis)
【 Symptoms 】 At the early stage of the disease, the abdomen of the sick shrimp appeared slightly turbid patches at 1 ~ 6 nodes, and then spread to the back of the body. Muscle color is cloudy, muscle cells are necrotic in batches, accompanied by mild or moderate blood cell exudation. The focus spread to the periphery, and the nucleus of myofibrillar membrane spontaneously proliferated. It is reported that 40% of shrimp deaths are related to this disease. The disease can occur in young shrimp, young shrimp, adult shrimp and overwintering parent shrimp. Osmotic pressure imbalance and secondary bacterial infection may occur in the late stage of the disease.
【 Etiology 】 This disease is mainly caused by the environment, not by microorganisms or parasites. Some water quality is polluted by chemical substances because of high water temperature, high stocking density and low dissolved oxygen, especially when these factors suddenly change, diseases are prone to occur.
[Diagnosis] The symptoms of microsporidiosis and vibriosis are also manifested as muscle whitening, which should be carefully examined when judging. In the area of muscle necrosis, there may be other bacteria and fungi, so we should pay attention to identification.
【 Control methods 】 ① Pay attention to prevention, and reduce sudden changes in the environment when handling and transporting larvae, larvae and adults. (2) In the high temperature season, the water temperature in the aquaculture pond should be prevented from being too high or suddenly changed, and the water should be changed frequently, injected with new water and aerated. ③ Control stocking density. (4) once the disease is found, it should be kept in isolation immediately. If shrimp is treated in time and gets sick for a short time, it can restore health and reduce losses.
(6) Spiny hair atrophy (deformity)
【 Symptoms 】 At the beginning of the disease, the tail bristles bend and become shorter, then the tail spines and appendages further shrink, even the whole body bristles shrink, and the larvae are unable to swim, and then sink to the bottom of the pool. Although it can shed its skin, sometimes it hangs on the tail of the larva and it is difficult to shed it completely. This disease mostly occurs in fertilized eggs and larvae.
【 Etiology 】 The occurrence of this disease is related to the unsuitable physical and chemical conditions of water environment. In the water polluted by heavy metals, fertilized eggs can develop in the membrane, but it is not easy to break the membrane and hatch.
【 Prevention method 】 ① Protect the water quality and proper water temperature. ② When the content of heavy metal ions in seedling water is high, 5 ~ 10 mg/kg EDTA-Na2 (disodium EDTA) should be added.
(7) Black gill disease [disease] The gill color of shrimp changes from reddish brown to black, and the shrimp has difficulty breathing, leading to death.
【 Etiology 】 There are many reasons for shrimp black gill disease, which are generally as follows: ① The bottom of the pond is seriously polluted and there are many organic debris in the pond water. These debris attach to the gill filaments with the breathing water, which makes the gills black and affects the shrimp's breathing. ② The gill of shrimp is infected by fungi, such as black gill disease caused by Fusarium. ③ The content of metal ions in the bottom of the pond is too high, which leads to poisoning and black gills. ④ Long-term vitamin C deficiency.
【 Preventive measures 】 Take the following preventive measures according to the causes: ① Sterilize regularly to reduce the possibility of bacteria and fungi breeding. (2) Pumping out the sludge at the bottom of the pond, so as to reduce the breeding opportunities of pathogens. ③ Avoid long-term use of copper sulfate drugs. If necessary, citric acid should be added at the same time to avoid copper deposition. ④ Vitamin C was added to the feed.
[Treatment] It is necessary to determine the real cause in order to prescribe the right medicine. The details are as follows: (1) Heavy metal poisoning should be treated with large change of water, adding citric acid and EDTA-Na2. ② Add enough vitamin C into the feed.
(8) Fusarium disease (or black gill disease)
【 Symptoms 】 This disease is found in eggs, larvae and adults. The gill of diseased shrimp is orange or bright brown in the early stage, then gradually darkens and finally turns black, so some people call it black gill disease. The bacteria can also parasitize on the appendages and body walls of shrimp, and the parasitic parts are also black. This disease leads to gill dysfunction and affects the normal breathing of shrimp. The disease can kill 90% larvae, and it is one of the most harmful diseases in aquaculture.
[Pathogen] Fusarium, also known as Fusarium or crescent, is a semi-knowing fungus and an incomplete fungus commonly found in soil and seawater. The most obvious feature of this strain.
Its macromolecules are sickle-shaped or round, with 1 ~ 7 walls. Oval and oval small molecules can also be formed under artificial culture conditions. When the conditions are not good, thick-film spores will form and then attach to other larvae to germinate into new mycelium. The diagnosis method of this bacterium is: the tissue damaged by Fusarium is made into immersion liquid and examined by anatomical mirror. When boat-shaped macromolecular spores are found on the surface or inside the wound, they can be diagnosed as Fusarium.
【 Control method 】 Fusarium isolated from the focus can grow in the medium with pH of 3 ~11and salinity of 0 ~ 10, which shows that it is a fungus with strong vitality. Therefore, it is impossible to control the growth of this bacterium by changing the pH value or salinity of the shrimp pond. So far, no drugs have been found at home and abroad to treat the confirmed Fusarium infection or prevent the spread of the disease. It is suggested that the source of molecular spores of Fusarium should be eliminated, the diseased shrimp should be destroyed and thoroughly disinfected with 2 ~ 10 mg/kg potassium permanganate solution. Japanese shrimp pond with 6.2 mg/kg in sodium dichloroisocyanurate can effectively kill conidia of Fusarium.
(9) Intermediate adolescent diseases
【 Symptoms 】 The disease has a specific incidence type, and a large number of deaths occurred within 1 1 ~ 24 days during seedling raising. However, the mortality rate decreased obviously after the 24th day, and the death peak was 14 ~ 18. Larvae in the 1 ~ 5 stage are sensitive to the disease, but they are resistant in the later stage. If the first stage larvae are raised in infected water, similar symptoms will appear within 4 ~ 5 days. It can be considered that the incubation period of the disease is about 5 days. The diseased larvae appear weak, spiral and don't eat. According to dissecting microscope's examination, epithelial tissue fluid cells in hepatopancreas and liver decreased obviously, and tissue cavities increased correspondingly. Spherical colonies were occasionally seen in the hepatopancreas lumen, and the striated muscle in the lumen was obviously degenerated. Infected larvae lose their normal body color and turn gray-blue, while the epithelial tissue of appendages appears "goose egg"-like processes. Bacterial colonies from histopathological sections were confined in the hepatopancreatic cavity and there was no bacteremia. No pathogenic bacteria were identified. But Vibrio has been isolated from diseased larvae.
【 Etiology 】 Bacterial toxins play a role in hepatopancreatic diseases. Other pathogenic factors include heavy metal elements, organic synthetic agents (pesticides), other biotoxins or malnutrition, but it is still unknown which one works.
[Prevention and control methods] All kinds of chemical treatment methods have been tried, but they have no effect. The only measure after the onset is to isolate all infected larvae and disinfect them thoroughly. Someone once used 0.4 mg/kg sodium difluorstyrene as a disease prevention agent.
(10) vibriosis
【 Symptoms 】 The muscles of diseased shrimp are opaque and white. Some diseased shrimps have black ulcers on their shells, black spots on their gills, head breastplate and ventral side, and black and brown dirt attached to their gills. After washing, the gill surface is gray or khaki, and the gill becomes thick and brittle. Finally, sometimes the gill filaments are damaged, and the tissues fall off or become vacuoles. We can see (under the microscope) active bacilli. Gram staining was positive and curved. This disease is more common in young shrimp and adult shrimp. The activity of diseased larvae is obviously weakened, mostly swimming slowly at the bottom, with weak phototaxis, slow growth of larvae, prolonged metamorphosis or inability to metamorphose, curled abdomen, white body color, no feeding, and adult shrimp floating on the water (or swimming along the edge) without direction. Some floated to the shore, moving slowly and slowly. The liver of diseased shrimp is white except for a small part above the breastplate of the head. The infection rate of the disease is very high, and the mortality rate of infected larvae or adults can be as high as 100%.
[Pathogen] The most common bacterial diseases of shrimp are caused by Vibrio. Vibrio is a common bacterium in seawater, fresh water and shrimp. According to the investigation of bacterial community in Macrobrachium rosenbergii nursery by Andreson et al. (1989), the number of bacteria on the body surface of Macrobrachium rosenbergii larvae (4th-6th stage) is1.4×105 ~ 5.7×105, belonging to/kloc-. Vibrio can be isolated from many diseased shrimps, such as brown spot disease and intermediate larva disease listed in this chapter. In addition to the watchcase, bacteria can be separated from shrimp intestine, hepatopancreas and muscle. Therefore, it is necessary to carry out infection test on sick shrimp to isolate Vibrio. If you can get the initial symptoms, you can be sure that it is the pathogen. There are many reports about the death of shrimp caused by Vibrio, but few can draw a clear conclusion.
【 Prevention method 】 Prevention is the main method of this disease. (1) Thoroughly disinfect the nursery pool before use, use 100 ~ 200mg/kg bleaching powder and 10 ~ 20mg/kg potassium permanganate, rinse the remaining drugs repeatedly with clear water, and filter and disinfect the nursery water. (2) Remove the dirt at the bottom of the pond every day during seedling raising. (3) Larvae in diseased ponds should not be brought into other nursery ponds. (4) Reduce seedling density and feed properly to prevent excess feed from rotting. ⑤ dosage: oxytetracycline 1 ~ 2mg/kg (powder), furacilin 0.5 ~ 1mg/kg (powder), spilled in the whole pool, 1 time, once every other day, 2 ~ 3 times in total, and bleaching powder 3mg/kg. ⑥ It is reported that the garlic shrimp seedling vibriosis has a good therapeutic effect. The specific method is to peel garlic and mash it, and filter the juice to make it into 5 ~ 10 mg/kg (according to the severity of the disease) for 24 hours. Garlic has low cost and can be used as a broad-spectrum fishery medicine to treat shrimp diseases.
The content of this article comes from: Natural Resources Protection by China Agricultural Publishing House.