Shrimp mortality situation and some preventive measures

In recent days, due to severe drought, the water environment in rivers, canals and ponds has changed greatly, causing adverse effects, causing shrimp in many areas to die at a fairly high rate.

Accumulated from the beginning of the year until now, the area of ​​industrial shrimp farming that died is 407.92 hectares, extensive and improved extensive shrimp farming is 3,619.5 hectares. The results of monitoring the water environment for aquaculture by the Department of Aquaculture of Ca Mau show that the environment is changing in a negative direction, which is unfavorable for farmed shrimp: Salinity, temperature, pH... are increasing, some areas deep in the inland water sources show signs of pollution, NH3, H2S... content is quite high, exceeding the appropriate threshold for farmed shrimp due to discharge from ponds with dead shrimp and poor water exchange capacity.

The cause of the disease that causes shrimp deaths is acute hepatopancreatic necrosis syndrome, a very dangerous disease. Acute hepatopancreatic necrosis syndrome occurs in both black tiger shrimp and whiteleg shrimp in intensive and semi-intensive farming. The stage of shrimp death is sometimes very early, about 1-2 weeks old. The easily recognizable symptoms are that the shrimp stop eating, swim slowly, have thin shells, and pale shrimp color; the hepatopancreas shows signs of swelling, softening, atrophy, and mass death; the disease occurs year-round, but is most severe from April to July. According to the Directorate of Fisheries, initial research results determined that the cause of acute hepatopancreatic necrosis syndrome is due to farmed shrimp being infected with Vibrio along with phage (which can be understood as a parasitic virus in Vibrio) when transferring toxic genes to bacteria that cause death. The risk of outbreaks of hepatopancreatic necrosis syndrome in each farming area depends on the quality of shrimp seed and the environmental conditions of the pond (pesticide residues, low dissolved oxygen, high salinity, large day-night temperature fluctuations, organic pollution in the pond). Shrimp seed produced in many hatcheries are of poor quality: Infected with Vibrio bacteria, showing abnormal signs in the hepatopancreas, even having hepatopancreatic necrosis right at the hatchery.

It is forecasted that in the coming time, the weather will continue to be complicated, the hot weather may continue, interspersed with early season rains, which is unfavorable for farmed shrimp. The water environment for shrimp farming has not been improved, leading to the possibility of rapid disease spread and difficulty in control.

To prevent shrimp deaths from continuing to occur and spreading widely. We recommend to shrimp farmers some measures to limit disease outbreaks in farmed shrimp as follows:

Due to the complicated weather conditions, the water environment in rivers and canals is polluted and difficult to improve, and the disease is likely to spread widely. It is recommended that farmers should not rush to release the breed at this time, but wait until the weather is stable and the water environment is improved before releasing the breed again, to avoid damage caused by the disease. After each crop, it is necessary to dry the bottom of the settling pond and the breeding pond to destroy pathogens, mineralize and improve the bottom environment. The best time to dry the pond bottom is 3-4 weeks.

During the pond preparation process, a settling pond is required to treat and store water to promptly supply to the pond when necessary; for industrial shrimp farming, it should be noted that chemical disinfection should not be carried out in the pond, it is best to treat it in the settling pond, then pump it into the pond. During the process of coloring the water in the shrimp pond, inorganic fertilizers should not be used, it is best to use biological products and use a mixture of molasses + rice bran + soybean powder in the ratio of 3:1:3, incubated for 12 hours, with a dosage of 2 - 3kg/1,000m3 of water.

For ponds that are being stocked, it is necessary to add water to the pond to ensure the adaptation requirements for the shrimp's life activities, avoid letting the pond become too shallow, which will cause the water temperature to increase, affecting the shrimp's growth and making the shrimp susceptible to shock, infection and death. Note that the water pumped into the pond must go through a settling pond and be treated to avoid contamination with pathogens, organic substances from the outside and avoid causing shock to the shrimp.

When releasing shrimp for farming, it is necessary to test for viral diseases. If possible, test for Vibrio bacteria (V.parahaemolyticus, V.harveyi, V. vulnificus). Select good quality shrimp seeds. In particular, it is necessary to select large shrimp seed production enterprises and facilities that apply advanced technology to ensure quality.

It is necessary to regularly monitor the environment and health of farmed shrimp to promptly handle and overcome any unusual developments. Adjust the pond environmental factors to ensure they are within the appropriate threshold for the growth and development of farmed shrimp: pH from 7.5 - 8.5; salinity from 15 - 25‰ for black tiger shrimp, from 5 - 25‰ for white-leg shrimp; temperature from 27 - 320C; dissolved oxygen >4mg/l for black tiger shrimp, >6mg/l for white-leg shrimp; alkalinity from 80 - 120 mg/l; transparency from 30 - 40cm; NH3 < 0.1mg/l; h2s < 0.01mg/l. Note: it is necessary to arrange a water fan system and fan running time to ensure sufficient oxygen supply for the respiratory needs of farmed shrimp, especially at night. Increase fan running time or increase fan system when the weather is unfavorable such as hot sun or prolonged rain.

Periodically use products such as lime, dolomite, especially biological products to treat, improve and stabilize the environment to help shrimp adapt and grow well.

Supplement the feed with products that enhance resistance such as vitamin C, Beta Glucant, premixes, etc. It is important to note that when choosing products for shrimp farming, especially biological products, you must choose products from reputable companies and buy from reliable businesses to get good quality products.

Should be stocked at low density: For black tiger shrimp, stocking density should be from 15 - 20 shrimp/m2, for white leg shrimp, stocking density should be 40 - 60 shrimp/m2 to facilitate care and management, less fluctuation in the farming environment, minimizing disease outbreaks. Use good quality feed, chemicals, biological products, on the permitted list, clearly labeled, with expiry date.

When detecting dead shrimp, farmers must not arbitrarily discharge waste into the outside environment, but should immediately report to local authorities for inspection and handling according to regulations. For dead shrimp ponds, the time to renovate by drying and using disinfectants must be at least 1-2 months to destroy pathogens, decompose toxins, improve the quality of the pond/farm or switch to raising other objects.

Shrimp farmers need to apply the shrimp farming process to limit disease as instructed by the Directorate of Fisheries. This is a farming process that has been summarized from the production practices of many localities across the country and has been widely deployed with quite high results; it is necessary to pay attention to implementing some of the above measures to limit the death of farmed shrimp, achieve high efficiency in production, and contribute to stable and sustainable economic development.

According to Congnghiepxanh