The "four no's" in shrimp disease prevention and control.

(Baonghean) - Given the complex disease situation affecting shrimp farming at the beginning of the 2017 farming season, disease prevention and control, as well as environmental protection in farming areas, are pressing issues today.

Specifically, implementing the "Four No's" – no releasing diseased shrimp fry, no supplying untreated water to the ponds, no concealing diseases, and no discharging untreated wastewater or dead shrimp carcasses into the environment – ​​is a good solution that shrimp farmers should adhere to.

According to the Nghe An Department of Animal Health, the area of ​​shrimp farms infected with disease in the first crop of 2017, as of May 10th, was 69.4 hectares, mainly concentrated in Quynh Xuan and Quynh Di communes in Hoang Mai town; Quynh Bang, Quynh Luong, and An Hoa communes in Quynh Luu district; Nghi Thai commune in Nghi Loc district; and Hung Hoa commune in Vinh City.

The disease mainly appears in whiteleg shrimp at stage 6 (60 days after stocking), most commonly between 20 and 49 days, with the most common test result being white spot disease. Therefore, for the next farming season to be successful, shrimp farmers need to thoroughly implement the "Four No's" in disease prevention and control.

Farmers in Quynh Thanh commune (Quynh Luu district) use lime powder to treat shrimp ponds. Photo: Viet Hung

First, do not fill the fish pond with untreated water.

Implement pond renovation work according to proper technical procedures to eliminate residual pathogens in the ponds and limit disease outbreaks, specifically:

Step 1: Drain the ponds and holding ponds. Remove any pests in the ponds (shrimp, crabs, snails, insects, unwanted fish, etc.). Remove bottom mud, repair the banks, and repair the water inlet and outlet pipes.

Step 2: For earthen ponds, apply agricultural lime powder and let the pond bottom dry for at least 30 days. The amount of lime should be 3-3.5 tons/ha. Thoroughly harrow the bottom to allow the lime to penetrate and kill any remaining shrimp, crabs, snails, insects, and unwanted fish, disinfect the mud, detoxify (heavy metals, H2S), and neutralize the pH.

For ponds with a liner: The liner needs to be removed, cleaned thoroughly, disinfected, and the pond washed clean. Then, lime (CaO) mixed with water to form a paste should be applied to the gaps in the liner.

Before supplying water to the pond, it must be treated to eliminate pathogens, unwanted fish, predatory fish, crustaceans, mollusks, etc. Use chlorine at a concentration of 25-30 ppm, with 65-70% activity (depending on the percentage of active chlorine in the chlorine), dissolve the chlorine in water, spread it evenly throughout the pond, and use water aerators or water pumps for about 3-4 hours continuously. After 3 days, when the effect of free chlorine has worn off, we can supply water to the pond.

Secondly, do not release shrimp larvae that carry diseases.

Select shrimp juveniles of the same age and uniform size: Postlarvae 15-20 (for tiger shrimp) and P 10-15 (for whiteleg shrimp), with a size variation of no more than 10%. Appearance: well-proportioned, straight antennae, no bent tails; shrimp should be light grayish-blue or light grayish-brown; swim quickly, cling to the tank walls, and when placed in a rotating basin, the shrimp should cling to the water current and swim against the current, not gathering in the center of the basin when the water current stops. Microscopic observation: The shrimp's intestines should be full of food, the intestine/muscle ratio in the sixth abdominal segment should be 1/4; the dorsal muscle should be transparent or bright blue; there should be a star-shaped pigment band running along the edge of the abdomen; the shrimp should not be infected with White Spot Syndrome Virus (WSSV), Yellow Head Virus (YHV), or MBV (if infected with MBV, the rate should be < 20%); the shrimp should not have any other organisms.

Third, don't hide your illness.

When disease occurs in shrimp ponds, it is necessary to immediately report it to local veterinary officers to determine the extent of the damage and receive support in the form of chlorine disinfection to prevent widespread outbreaks. Shrimp farmers need to uphold their sense of community responsibility and avoid failing to report disease outbreaks to local authorities, instead quietly handling the situation themselves. This makes it difficult for relevant agencies to manage the situation, creating opportunities for disease to spread and develop. More worryingly, when ponds are infected, farmers often handle the situation themselves, making it impossible to determine the concentration and dosage of medications and chemicals needed to completely eradicate the pathogens. Even more dangerous is when some households do not treat the ponds with medications and chemicals but instead discharge wastewater directly into the environment.

Fourth, do not discharge untreated pond water that has not been treated to eliminate pathogens into the environment.

The disposal of dead shrimp due to disease requires careful attention and thorough handling. Shrimp farmers need to collect all dead shrimp from their ponds and bury them far from the pond banks to prevent the spread of disease and the development of viruses and bacteria. Collecting dead shrimp not only helps protect the environment of their own ponds but also contributes to protecting the environment of the surrounding farming area.

In addition to implementing the "Four No's" in disease prevention and control mentioned above, the stages of remediation, dredging of mud after pathogen treatment, and care and management must be carried out strictly according to the recommendations of the relevant authorities. Thoroughly applying the "Four No's" in disease prevention and control is how shrimp farmers protect themselves.

Tran Trung Thanh