CATDOLL : CATDOLL: What are the most common diseases of crabs in aquaculture?

1. Tremor disease) [Pathogen] The disease may be caused by viruses and bacteria. According to reports by Lu Hongda et al. (1999), a non-enveloped, spherical ribovirus is the pathogen of the disease. When it is not pathogenic, it resides in the intestines. Once it invades the central nervous system and heart, it will cause great harm. Some people have also observed another virus that is slightly smaller than cells, located in the endoplasmic reticulum of cells, and can form inclusion bodies. In addition, Vibrio and Aeromonas hydrophila have been isolated from crabs with the disease. Unclean, fertile, and highly polluted water, mixed crab species or inbreeding, excessive stocking density, uneven specifications, and unbalanced nutrition intake of crabs are prone to this disease. [Symptoms and pathology] In the early stage of the disease, the limbs of the diseased crabs can still be straightened, but then the muscles atrophy and the legs cannot be extended. The diseased crabs are unstable and have difficulty turning over. They spit foam at the mouth, are weak and cannot crawl, and tremble continuously. Sick crabs lose their appetite and stop eating, do not shed their shells, accumulate water in their bodies, and die after 3-4 days. [Epidemic characteristics] The disease mainly harms 2-year-old crabs and adult crabs. The incidence of crabs grown that year is generally low. The weight of the diseased crabs is 3-120 grams, and the highest incidence is in crabs over 100 grams. The general incidence rate can reach more than 30%, and the mortality rate is 80%-100%. It spreads rapidly and causes great harm. It often takes only 15-30 days from onset to death. The disease season is from May to early October, and August to October is the peak season. The epidemic water temperature is 25-35℃, and the epidemic is serious along the Yangtze River, especially in Jiangsu and Zhejiang provinces. [Expert recommended prescription]: Prevention: ①Clear the pond thoroughly before stocking and remove excess silt; ②Plant more aquatic plants in the crab pond, and the coverage should reach 50-60%; ③Strengthen water quality management and keep the water clean; ④Pay attention to the nutritional balance of feed and appropriately increase plant bait; ⑤Regularly spray the whole pond with Fangcao Xieping or Junbiqing for disinfection. Treatment: Spray the whole pond with Fangcao Xieping or Junbiqing externally (the former is used for three consecutive days, and the latter is used every other day), and take Fangcao Junwei and Sanhuang powder internally for 5-7 consecutive days. Use another course of treatment after the symptoms disappear to consolidate the therapeutic effect.

2. Black gill disease [Pathogen] It is preliminarily believed that the disease is caused by bacteria. In the late stage of crab breeding, the deterioration of water quality is the main cause of the disease. [Symptoms and lesions] In the early stage, some gill filaments of diseased crabs turn dark brown, and as the disease progresses, they all turn black. Diseased crabs move slowly, have difficulty breathing, and sigh. [Epidemic characteristics] The disease mainly harms adult crabs and often occurs in the late stage of crab breeding. The incidence rate is 10%-20%, and the mortality rate is high. The main epidemic seasons are summer and autumn. [Expert recommended prescription]: Prevention: Keep the water clean and add new water frequently in summer; use Fangcao Xieping, Fangcao sterilization water purification or Fangcao sterilization water purification liquid to spray the whole pond once every half a month during the disease season. Treatment: Spray the whole pond with Fangcao Xieping externally, and take Lanjilingsan + Sanhuang powder + Fangcao multivitamin internally for 3-5 days.

3. Limb rot disease [Pathogen] This disease is caused by pathogenic bacteria infection after the epidermis is damaged during grafting, transportation, stocking or invasion by enemies during growth. The pathogen has not been determined yet, and some people think it may be a Vibrio. [Symptoms and lesions] The abdomen and appendages of the diseased crabs rot, and the anus is red and swollen. [Epidemic and harm] This disease mainly harms young and adult crabs, and the main epidemic season is June-October. [Expert recommended prescription] Prevention: During the breeding process, be careful to avoid using crabs and eliminate the enemies that harm crabs, such as mice, frogs, etc. Treatment: Spraying the whole pond with aromatic grass fungus or aromatic grass sterilization water purification liquid can control the spread of the disease.

3. Sessile ciliate disease [Pathogen] The pathogens are many species of Ciliates, Trichodea, Sessile suborder, among which the main ones that cause disease to crabs are polycystic ovary, in addition to bellworms, monocystic ovary, truncate worms, gastrocnemius (Gastrionauta sp.) and lntransty-lumpalaemini sp. are also one of its pathogens. Pond water is too fertile and the water is not changed for a long time, which is the cause of the disease. [Symptoms and lesions] When sessile ciliates parasitize on river crab larvae, they are often distributed in the head, thorax, abdomen, etc. They can also parasitize on the eggs of egg-bearing crabs, but rarely on the appendages. The larvae of diseased crabs parasitized by this type of ciliates are covered with yellow-green or brown. The normal activities of crab larvae are affected, the food intake is reduced, the breathing is blocked, and the molting is difficult, causing a large number of larvae to die. Sessile ciliates parasitize on juvenile and adult crabs, mostly distributed in joints, walking legs, carapace, forehead, appendages and gills. The body surface of diseased crabs is more polluted, and their activity and feeding ability are weakened, which in turn leads to more parasitism of sessile ciliates. The burden of diseased crabs is increased, the water flowing out of the gills is slow, the antennae are insensitive, and the body surface and appendages of diseased crabs feel greasy when touched. Diseased crabs usually die around dawn. [Epidemic characteristics and hazards] It can harm river crab larvae and adult crabs, but it is more harmful to river crab larvae in seedling ponds. Once this type of ciliate enters the nursery pond with the water flow, it will quickly reproduce in the pond, causing a large number of larvae to die. Adult crabs infected with this disease, even if they do not die, will also affect their commercial value. The disease is very likely to occur when the water temperature is 18-20℃ and the salinity is 3. This disease has been found in crab breeding areas in Jiangsu, Hubei, Jiangxi and other provinces in my country. [Expert recommended prescription] Prevention: ① Maintain appropriate stocking density; ② Change new water frequently to keep the water clean, and feed appropriate feed to promote molting. Treatment: Spray the whole pond: ① Shrimp and Crab Ping 500g/mu.m or Fangcao Xianmie 50g/mu.m, for 3 consecutive days; after 3 days, spray Fangcao Jundi 200g/mu.m once for external use, and take Shrimp and Crab Molting Ping 500-750g/100Kg feed internally to promote molting.

5. Saprolegniasis [Pathogen] The pathogen is Saprolegnia, whose species has not yet been identified. The main cause of the disease is that other diseases occur during transportation, causing crabs to be injured and fungal spores to invade; in addition, the stagnation of water flow and temperature can also cause the eggs to be infected. [Symptoms and lesions] Grayish-white cotton-like lesions appear on the surface of crab eggs or the body and appendages of diseased crabs, especially on wounds. The tissue at the wound site ulcerates. The diseased crabs move slowly, have a loss of appetite, and are thin. They have difficulty molting and die. [Epidemic characteristics] The disease can infect crab eggs, larvae, and adult crabs, and it can occur in any area. The incidence rate is high, and the disease of crab eggs and larvae can easily cause a large number of deaths. [Expert recommended prescription] Prevention: ① Be careful during the process of catching, transporting, and stocking to avoid injuring river crabs. ② Before river crabs molt, add some animal feed to promote molting. ③ During the seedling raising period, keep the water clear and pay attention to heat preservation. Treatment: Spray the entire pond with Water Mold Cleaner (1 bag/mu・m) for 3 consecutive days.

6. Edema [Pathogen] This disease is mainly caused by the injury of the crab's abdomen and the parasitism of pathogens. The pathogen has not yet been determined, and some people believe it is Aeromonas hydrophila. [Symptoms and lesions] The crab's anus is red and swollen, and the abdomen, belly button and the lower part of the back shell are swollen and transparent. The crab crawls on the edge of the pond, moves slowly or does not move, refuses to eat, and eventually dies in the shallow water at the edge of the pond. [Epidemic characteristics] This disease mainly harms young and adult crabs. Although the incidence rate is not high, the mortality rate of infected crabs can reach more than 60%. Summer and autumn are its main epidemic seasons. The main epidemic temperature is 24-28 ℃. [Recommended prescriptions by herbal experts]: Prevention: ① During the breeding process, especially when the crabs are molting, try to minimize disturbing them to avoid injury; ② In summer, add new water frequently and feed more fresh feed and fresh plant bait. Treatment: Spray the whole pond with Junbiqing or Fangcao Xieping, and take Yubingkangsan or Fangcaojunling internally at the same time.

[Important Tips]: After the symptoms disappear, it is recommended to continue taking the medicine until the end of the course of treatment to avoid cross infection and recurrence of the disease.

Tremor disease, the pathogen comes from bacteria or viruses;

Prevention and treatment methods: ecological disease prevention is the main method, supplemented by drug treatment, and attention must be paid to improving the quality of the breeding environment;

Sick crabs can be treated with a combination of external and internal methods. External disinfectants can use chlorine dioxide or compound iodine and other disinfectants, followed by water adjustment with bio-water and compound probiotics. For internal use, detoxifying VCE, liver-protecting Chinese medicine, allicin, etc. can be added to the feed and fed for 5-7 days.