How to Prevent Shrimp WFS Outbreak In the Early Stage?

In recent years, shrimp white faeces (WFS) have often appeared during the culture of Penaeus vannamei. In this case, the appetite of P. vannamei is reduced, grow this slow, yield is low, and the feed coefficient is high. In severe cases, shrimp weight decreases and "dry shrimp" appears. As a result, "EMS" occurred and the damage was more serious. 

Especially in the high-temperature season, the highest temperature is as high as 37 degrees Celsius. During the period, the white shrimp often hits with rain. 

Most farmers do not understand the living habits of the P. vannamei. Excessive feeding and improper management in high-temperature weather caused large-scale WFS outbreaks of P. vannamei. The area with the highest incidence rate reaches 70%.

Onset symptoms

In the early stage, the symptoms of sick shrimp are not obvious, but the appetite is reduced. As the disease progresses, more and more sick shrimps do not eat feed. Examination of the downwind vent surface reveals floating white faeces. Detection of sick shrimps shows that their intestines are not full, causing"broken intestines" and jejunum, and the hepatopancreas begins to shrink, become smaller, and have a fuzzy appearance. Some sick shrimps have symptoms such as red beards, red legs, thickened intestines, and more white faeces floating on the water. 

When the disease progresses further, a small number of sick shrimps will die or crawl sideways. At this time, the sick shrimps will grow slowly or stop growing, and some will lose weight and become"dry shrimps". The size of the shrimps in the pond will be very different, and the yield is low. The FCR increases.

Further anatomy of the diseased shrimp showed that the hepatopancreas of the pre-sick shrimp decreased in fat, with little change in size. In the middle stage, the size of the hepatopancreas became smaller and the foregut became white. As the disease progressed, the intestine gradually became white from front to back. 

When the disease is severe, the entire intestine becomes milky white, showing a "white intestine". The pathological section observation of the lesion showed that some of the glands in the hepatopancreas of the diseased shrimp were atrophy, most of the glands were normal, a small amount of shrimp intestinal mucosal epithelium was deformed, and the intestinal wall cells were proliferated. At this time, the shrimp still had a strong digestion and absorption function.

In the middle stage of the disease, the hepatopancreas is severely atrophy, the ductal epithelium falls off, and the atrophic part accounts for an increasing proportion of the entire hepatopancreas. The intestinal mucosal epithelium also begins to fall off, and the proliferation of intestinal wall cells is more serious. The intestinal mucosal epithelium and proliferative cells form"white faeces". During this period, the digestion and absorption functions of shrimps are severely reduced.

In the later stage, the hepatopancreas ducts atrophy, epithelial shedding, necrosis, and multiple granulomas of varying sizes are gradually formed. Intestinal wall cells continue to proliferate and fall off. At this time, the sick shrimp can no longer recover. From the perspective of anatomy and pathological sections, "white faeces" starts from hepatopancreas lesions, formed by epithelial cells and proliferative cells shed after hepatopancreas and intestinal lesions, not normal faeces formed after feed digestion.

If you pay attention, you will find that shrimp WFS is very common in high temperature, high density, high protein and high feeding amount situations, while it is rare in the low-temperature period, winter shed shrimp, low density, polyculture and sparsely cultured shrimps. During the period of high temperature, the shrimp feed fiercely and the burden of hepatopancreas is heavy. In addition, the breeding of seedlings now tends to be fast and large, and the research and development of feed also focus on growth speed. Long term feeding of high protein feed to promote growth will undoubtedly increase the digestive burden of hepatopancreas.

At present, studies have shown that shrimp WFS may be caused by a pathogen similar to vibrio, but the pathogen is only one of the causes of shrimp WFS enteritis. In addition, sudden change of weather, "bankrupt algae", deterioration sediment, mildew of feed, the outbreak of cyanobacteria and damage of digestive functions are all the inducing factors or aggravating factors of"WFS". To control the occurrence of WFS comprehensively and effectively, we need to take various measures:

1. Prevention and treatment should be done earlier

It takes a process for bacteria to enter the shrimp body. If you don't see the shrimp WFS, it does not mean that it has not started yet. At this time, prevention is more critical. When there are more WFS, it is already more serious and the liver hasbeen diseased. At this time, medication is used to kill external pathogenic factor and ignore the protection and repair of the shrimp itself, which willcause damage to the shrimp itself. , The physique of the shrimp deteriorates, and the hepatopancreas and stomach are injured. This is also the reason why it is difficult to feed the shrimp after the WFS treatment. Therefore, WFS should be prevented and dealt with early.

2. From the perspective of traditional Chinese medicine, "sweet potato treats WFS"

I don’t know when this recipe that sweet potatoes can treat WFS has been spread. Traditional Chinese medicine has proposed that "medicine and food are of the same origin." However, many medicines cannot be used as daily foods because the medicinal properties are very biased, cold or hot, the food properties should be relatively neutral. Sweet potato is a medicinal and edible thing for humans. The weakness is that it has very weak medicinal properties and very limited efficacy. This is why the sweet potato treatment does not affect in many cases.

3. The medicinal properties and selection of drugs

At present, many farmers often use Chinese herbal medicines in the treatment of WFS, but most of them use some Sanhuang, Wuhuang and the like. The Sanhuang and Wuhuang are used to treat heat syndrome and belong to the traditional Chinese medicine for clearing away heat and detoxification. Traditional Chinese medicine is not "non-toxic and no side effects" as the manufacturers advertise. "Every medicine has its side effect medicine" is what Chinese medicine says. 

Although Sanhuang and Wuhuanghave some symptomatic effects on WFS, they are more potent and are not suitable for diseased or weak shrimps. The damage to the shrimps is relatively large, and the overall harm is greater than the benefits. Especially when the shrimp hepatopancreas is shrinking, the use of Sanhuang and Wuhuang will aggravate the condition.

In aquatic animals, there are not only heat-clearing agents to protect the liver, but also warming and tonic, such as bile acids. Bile acids are mainly based on supplementing bile acids and repairing liver cells, combined with multi-vitamins to promote the recovery of body functions.

Since many drugs are decomposed and transformed by the liver of shrimp, when treating or preventing liver disease of P. vannamei, it is important to choose products that have no side effects on the liver. Bile acids should be selected first, which will not increase the burden on the liver, but can also help the liver to detoxify, repair damaged liver cells, and effectively prevent the occurrence of enteritis, EMS, and WFS.

Treating "WFS" should be based on the principle of "preventing no disease first, treating the disease early, focusing on prevention, and combining prevention and treatment". Studies have shown that WFS is the"left-over" tissue on the hepatopancreas. Then we need to improve the physique of shrimps, improve and optimize the water environment, and cut off cutoff the spread of pathogens to regulate the hepatopancreas, which can prevent WFS.