Macrobrachium rosenbergii is native to the Indo-Pacific region and lives in various types of fresh or brackish water waters. Since the 1960s, it has been transplanted to some countries and regions such as Asia, Europe, and the Americas. Muscle white turbid disease of Macrobrachium rosenbergii, also known as white body disease and white tail disease, is a disease that has occurred in Macrobrachium rosenbergii in the larval stage in recent years. The diseased shrimps have symptoms of white turbid muscles, white spots or white tails, which can occur within a few days. A large number of deaths occur within a day, and the mortality rate can be as high as more than 60, which has become a major hazard to the current breeding and breeding of Macrobrachium rosenbergii. Studies have shown that the causative agent of Macrobrachium rosenbergii muscle white turbid disease is Macrobrachium rosenbergii nodavirus, and the transmission route is mainly vertical transmission, but its horizontal transmission also has a strong ability to infect. From 2002 to 2003, the author applied the virus diagnosis technology of ELISA method and RT-PCR method to conduct research on virus-free seed breeding technology of Macrobrachium rosenbergii, and successfully provided virus-free seed shrimp and virus-free seed shrimp to major nursery and breeding areas in my country. seedlings and effectively prevent the prevalence of muscle white turbid disease in Macrobrachium rosenbergii.
Virus-free broodstock breeding
1. Seed selection From the end of April to early May every year, select high-quality, healthy and desalinated seeds produced by self-propagation or hatcheries with no history of disease. Specifications Shrimp larvae with a body length of more than 0.8cm, uniform individuals, strong constitution, and strong reverse swimming ability, and which have been tested negative by the TAS-ELISA method of Nodavirus in Macrobrachium rosenbergii.
2. For the temporary cultivation of shrimp seedlings, choose a cement pool or an earthen pool in a greenhouse that has isolation measures and has been strictly disinfected. The stocking density in the cement pool is 5,000 shrimps/square meter, and the stocking density in the earthen pool in the greenhouse is The density is 3,000 fish/square meter, the water temperature is 25°C, and the feed uses egg custard, shrimp flakes, Macrobrachium rosenbergii mixed feed with high nutritional value, etc. During the temporary breeding period, carefully observe the activity and feeding status of shrimp seedlings every day, and promptly select suspicious shrimp seedlings for virus testing. During the one-month temporary raising period, at least 7 virus tests were carried out and the test results were negative. After May 20, when the water temperature in the outer pond is above 22°C, the shrimp larvae will be put into a pond with isolation measures for culture. The pond should have no history of disease and be strictly disinfected before the shrimp larvae are stocked.
3. Pond culture: Pond culture is carried out from June to October. The management work is strictly carried out in accordance with the technical operating specifications of Macrobrachium rosenbergii culture. The growth status of shrimp larvae is regularly checked, and the ELISA method is used for virus detection.
4. Disinfection and isolation measures during the cultivation of shrimp larvae. During the temporary cultivation of shrimp larvae and pond cultivation, the water for cultivation should be sedimented and disinfected in the reservoir. At the same time, be careful not to use frozen wild water of unknown origin. Trash fish are used as aquaculture feed.
5. Broodstock selection Broodstock selection can be carried out in early October. Shrimps with strong physiques, complete appendages, and no lesions on the whole body should be selected, and the male to female ratio should be 2 to 3:1.
Intensive cultivation of broodstock during the overwintering period
1. Pretreatment of the overwintering pond. The overwintering pond should be soaked in 30ppm potassium permanganate solution for more than 1 week before use, and then brushed clean after clearing the pond. ,stand-by.
2. Regulation of suitable environmental conditions. During the winter, the water temperature should be controlled at 21°C to 22°C. In the early stages of overwintering, because the shrimps have just entered the greenhouse and are severely mechanically damaged, the water temperature can be appropriately increased by 1°C to 2°C. After the shrimps have increased their food intake and recovered their physical fitness, the water temperature can then be lowered to the overwintering water temperature.
3. Feed feeding Feed is the basis for the gonad development of broodstock. Feed feeding must not only ensure the nutritional needs of broodstock, but also ensure its palatability. During the winter, artificial compound feed can be used as the main feed, supplemented with animal feed, and multivitamins, immune polysaccharides, etc. are regularly added to the feed to strengthen the nutrition of the broodstock, enhance their immunity, and avoid the occurrence of broodstock diseases. Anorexia.
4. Strengthen management. The water source for breeding should be ensured to be free from pathogen contamination, and the overwintering water should be disinfected regularly. Tools and workshops in the greenhouse should also be strictly disinfected every day.
5. Conduct virus testing on broodstock regularly. Observe the feeding status and activities of broodstock every day. If suspicious broodstock is found, virus testing should be carried out immediately.
During the winter, ensure there is at least one virus detection record per month.
Breeding technology of virus-free seedlings
1. Pretreatment of water source: Fill the pond with water when the water temperature is low in winter, and use quicklime to disinfect the pond water. After 1 to 2 months of sedimentation and disinfection treatment, the water quality index of the pool water can reach a good state during the nursery season.
2. In the intensive cultivation of broodstock, throughout the nursery period, animal feed should be increased, and multivitamins, immune polysaccharides and other substances should be added to the feed. The daily feeding amount is the body weight of the shrimp. 5 to 7, and adjust the feeding amount at any time according to the feeding status of the shrimp, increase the amount and frequency of water changes to keep the water quality fresh, and promote the rapid maturation of the gonads of the broodstock to mate and spawn in the pool.
3. Disease prevention and control: Adopt comprehensive prevention and control measures that focus on prevention and emphasize prevention over cure. The nursery pool and nursery tools must be strictly cleaned and disinfected before and after use. After each shrimp fishing operation, thoroughly disinfect the broodstock pond with high-concentration potassium permanganate. When the seedling water enters the water, 200 mesh gauze can be used to filter the water source. Regularly conduct virus testing on larvae (especially desalinated larvae).
4. Develop a strict nursery area management system. In order to prevent the horizontal spread of Macrobrachium rosenbergii muscle white turbid disease, a strict nursery area management system can be developed. The main contents are as follows: ① The nursery staff strictly follow the operating standards for Macrobrachium rosenbergii nursery and disinfect the tools used for nursery in a timely manner. Build a disinfection pool at the entrance of the workshop to disinfect personnel at any time when entering and exiting the workshop. ②Customers who buy seedlings must disinfect their shoes and hands before entering the workshop. Customers who buy seedlings are strictly prohibited from touching the nursery water and shrimp seedlings. If they need to see the seedlings, the workshop management personnel will do so on their behalf.
Summary
1. Breeding virus-free broodstock is the key. The virus-free seed breeding technology of Macrobrachium rosenbergii can effectively prevent the occurrence of muscle leukosis. The key lies in whether it can effectively block the transmission route of the pathogen. The epidemiological investigation of the pathogen of Macrobrachium rosenbergii muscle leukosis shows that its main transmission route is carried and transmitted by broodstock. By tracking and detecting the broodstock seeds, isolation measures are taken during the whole breeding process to fully ensure Virus-free status of selected broodstock.
2. Intensive cultivation of broodstock and suitable environmental conditions during the production process are auxiliary measures for virus-free seed cultivation. Pathogens, shrimps, and the environment are an interactive and interconnected system. Under normal circumstances, the three are in a balanced system. If one of them changes, it will inevitably cause an imbalance in the entire system, leading to the occurrence of disease. The epidemiological investigation of Macrobrachium rosenbergii muscle white turbid disease has also verified this. Therefore, strengthening the nutrition of broodstock during the whole breeding process and adding multivitamins, immune polysaccharides and other substances to the feed can effectively improve the broodstock. The constitution and immunity of shrimp. In addition, appropriate environmental conditions must be ensured during larval cultivation.
3. Strict disinfection measures must be taken to prevent muscle white turbidity in Macrobrachium rosenbergii. Strict disinfection measures are an important guarantee for disease prevention. At present, almost all Macrobrachium rosenbergii hatcheries are built in epidemic areas. Disinfection measures are the key to ensuring that the hatcheries are not infected by neighboring disease farms. The nursery workshop has a strict equipment disinfection system. Necessary measures are taken for customers who buy seedlings and customers are restricted from entering the production area. Customers can only enter the seedling supply area. The hands and shoes of all personnel entering the production area must be strictly disinfected to ensure that no viruses are carried into the area. production area.