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South American white shrimp "death disease" in recent years more and more serious, more and more attention by farmers, many experts and technicians believe that the most important cause of death is liver and pancreatic necrosis, intestinal lesions and so on. Many manufacturers also directly describe "death stealing disease" as "shrimp jejunal and empty stomach stealing death disease". So what is the cause of the death of Penaeus vannamei in South America? How should we prevent and deal with it?
1. The process of shrimp "stealing death" disease
The "death stealing disease" of Penaeus vannamei is academically called EMS (shrimp early death syndrome) or "acute hepatobatic necrosis", which mostly occurs within 60 days of the breeding period, the color of the diseased shrimp is white and turbid and slightly red, the liver pancreas is enlarged, the texture is soft, the color is pale or yellowish, and then shrinks. This definition was proposed by the shrimp industry system in 2014. It is believed that the necrosis of the liver and pancreas of shrimp is the "death stealing disease", and He Jianguo, chief scientist of the shrimp system, believes that the "death stealing disease" is mainly caused by the amount of culture exceeding the amount of environmental capacity. In fact, since 2009, China's South American white shrimp farming has been suffering from "death stealing disease".
When the "death stealing disorder" first appeared, experts and technicians proposed different causes that may lead to the death of shrimp, such as the degradation of shrimp species, the deterioration of exogenous water, the high stocking density, etc., but they did not meet the views that everyone agreed with. Among them, it is accepted that the pathogen of shrimp jejunal and empty stomach death disease is Vibrio parahaemolyticus. Later, Huang Kai, a scientist at the disease prevention and control post in the northern region of the shrimp industry system, proposed that the "nodamura virus" is the pathogen that causes the viral death of shrimp. In the past two years, enterosporidium has been detected in the intestine, resulting in intestinal lesions and stealing death.
No matter what causes the shrimp to die, we must start from the details, one link after another to solve the mystery of the shrimp stealing death, since the cause of the death is not the only one, then the details in the analysis process are particularly important. After all, many of our farmers do not know how to analyze the causes, and the products that specialize in stealing death cannot deal with any cause of stealing death. Next, we analyze the main causes of death, and then look for ways to prevent and deal with them according to the causes.
Second, the causes of shrimp "death stealing" analysis
1. Bacterial infection steals death
After Vibrio shrimp infection, a large number of black spots are distributed on the surface of the body, and the intestinal pigment cells spread and turn red; the liver appears red first, and the death is sporadic, and the later death is a large number.
2. Death by virus formation
Hepatobic and pancreatic parvovirus and leukoplakia virus also cause death. Shrimp infection with the virus, first of all, because of Vibrio infection or deterioration of the water environment and other reasons, resulting in a decline in the physique of shrimp, the outbreak of virus in the shrimp body, resulting in stealing death.
3. Death by the deterioration of water quality
The phenomenon of dead shrimp appears at the bottom of the pond, and the muscles of dead shrimp are white and turbid, accompanied by incomplete shelling and broken whiskers. This phenomenon is common in high-density culture ponds. The main reasons are: (1) lack of oxygen at night at the bottom layer. Poor management of the substrate, excessive accumulation of organic matter, of course, poor feeding management, too much residual bait and feces. (2) Ammonia nitrogen is high, nitrite is high. (3) Poor water quality management. The shrimp appear gill swelling, yellow gills, black gills, etc., resulting in physiological hypoxia of shrimp, resulting in stealing death.
Judging from the softness and hardness of the shell, the death stealing situation can be divided into three points:
(1) Hard-shelled dead shrimp are usually caused by bacterial infection.
(2) Soft-shelled dead shrimp is usually caused by acute shelling of shrimp when a large number of shrimp are dehulled, the bottom of the pond is dehydrated, the water quality and substrate deteriorate or the shrimp is suddenly changed due to climate change.
(3) Both hard-shell dead shrimp and soft-shell dead shrimp are available, usually caused by unsuccessful dehulling.
4. Shrimp liver pancreas, intestinal lesions lead to stealing death
Lesions in the liver and pancreas of shrimp are usually due to the failure to protect the liver and pancreas during breeding. Poor management of water quality and substrate, and the proliferation of harmful bacteria; secondly, the nutritional supplement is not in place in the process, and the microbiotics and minerals are not replenished in time, resulting in the shrimp in a sub-healthy state, coupled with the continuous accumulation of harmful substances in the pond, such as algal toxins. Causes lesions in the liver and pancreas of shrimp. If it is not treated in time, slowly the intestine will also begin to develop lesions, and intestinal diseases such as white stool will appear. Thus there appears to steal death.
Third, the prevention of shrimp "stealing death disease"
To prevent the occurrence of shrimp death, it is necessary to do a good job in the management of the whole process. Prevention can start from the following aspects:
(1) Seed selection. Do not choose low-quality seedlings, especially those that have been bred with antibiotics, the liver, pancreas and intestines have been harmed. It will be very difficult to manage in the later stages.
(2) Water quality management. Aquaculture is to solve pollution, increase the self-purification capacity of ponds, and solve the problem of toxin residues. Toxins (especially algal toxins, such as cyanobacterial toxins, etc.) can affect the liver, pancreas, and intestinal health of shrimp, thus affecting the healthy growth of shrimp.
There are three criteria for good water quality: A, adapt to shrimp growth (no toxin residue); B, water quality is stable (of course, relatively stable); C, sufficient dissolved oxygen (sufficient dissolved oxygen) Many problems are not a problem. Therefore, the water quality can not only look at whether it is a good algae, but also depends on whether the water quality is stable.
(3) Substrate management. The bottom of the pond is the main activity area of Penaeus vannamei, and it is very important to eat and drink Lasa, so it is very important to do a good job in bottom quality management. Many parasitic (ciliate) infections, nitrite and other indicators exceeded standards, hypoxia, hydrogen sulfide production, and toxin accumulation are all related to poor management of the substrate. It is necessary to do a good job of regular bottom modification, and at the same time, it is also necessary to rationally use the bottom change product. The substrate also contains many toxins that need to be addressed. Prevent excessive accumulation of toxins, causing liver, pancreas, and intestinal poisoning, resulting in stealing death.
(4) Do a good job of disinfection regularly. In the breeding process, regular disinfection is good, and vibrio vibrio, povidone iodine, etc. with small irritation can be selected for disinfection to reduce the number of bacteria, especially Vibrio parahaemolyticus. Excessive numbers of bacteria may lead to disease on shrimp.
(5) Liver protection and intestinal protection. The protection of the liver and pancreas needs to start from the release of seedlings, and the whole process needs to do a good job of liver protection. The most important work of liver protection is to reduce liver and pancreatic poisoning and bacterial infection, to do this is first of all to improve the physique of shrimp, to ensure the health of the shrimp liver pancreas, intestines. Especially when the shrimp turn to liver, be sure to let the shrimp liver and pancreas fully develop.
