Dangerous and common diseases in shrimp
The Mekong Delta accounts for more than 80% of the country’s shrimp farming area and production and is a farming area with two distinct rainy and sunny seasons. In the dry season, factors such as high salinity and high temperature make it difficult for oxygen to dissolve in the water along with excess food and algae that is easy to explode, difficult to manage, easy to collapse, leading to depletion of dissolved oxygen sources in pond water. making the pond bottom anaerobic and prone to disease outbreaks for shrimp. In contrast, the rainy season is mainly caused by large fluctuations in environmental factors in the pond water followed by rains that easily shock shrimp and make shrimp more susceptible to diseases, especially when shrimp are shocked and easily susceptible to disease. Molting after rain is a great opportunity for pathogens to enter because shrimp have just molted very weakly, it is difficult to harden quickly when under severe stress.
Dangerous and common shrimp diseases include: acute hepatopancreatic necrosis disease (AHPND or EMS), microsporidian disease (EHP) and white feces disease (WFD or WFS). EHP and WFD are now very common concerns of shrimp farmers because there is no perfect solution to cure, and it seems that farming practice shows that these diseases are easy to superinfect in shrimp.
Acute hepatopancreatic disease (AHPND or EMS) has been identified by Dr. Loc Tran and Dr. Lighner as caused by Vibrio parahaemolyticus and now with the solution of adjusting the pond environment along with some drugs and herbs to treat 3-5 days shrimp will disease, so it is easier for farmers to control the disease.
EHP is caused by microsporidian spores, but recently the group of Microsporidian microspores has been classified as a fungus. In fact, farmers recorded EHP microsporidian disease common in the first 45 days of the culture. EHP disease, if infected from shrimp seed sources due to not being screened for the right test method (Nested PCR or Realtime PCR), the disease is easy to manifest in the first 30 days of stocking and if infected, it is easy to superinfect with hepatopancreatic disease. level (AHPND). In case of EHP infection from farm water, the disease is common in 30-45 days, in some cases later when shrimp reach 45-60 days of culture and in this case, EHP is easy to superinfect. with white feces disease.
White feces disease (WFD) or White stool syndrome (WFS) has been evaluated, researched and investigated with many different opinions on the causative factors including Vibrio sp., Gregarine and superinfection with EHP microspores; But so far, there has been no research confirming the main cause of white stool disease. However, recently Luis et al (2021) performed a superinfection experiment on shrimp infected with EHP with Vibrio parahaemolyticus taken from the intestines of shrimp with white feces disease, with interesting results, that shrimp with white feces and EHP disease will be severe. than in the presence of Vibrio parahaemolyticus.
In fact, this trait is almost the same across all organisms, including humans, which are susceptible to disease following shock factors. The same goes for shrimp, and most clearly acute hepatopancreatic disease and white feces disease are easily observed after environmental factors in the pond bottom exceed the tolerance threshold or after long hot days, after heavy rains, after the algae thicken and collapse, shrimp are very susceptible to hepatopancreas and white feces, including superinfection with EHP microspores. Therefore, managing the shock factors by using anti-stress feeding strategies, managing the environmental factors in the optimal range, and having different solutions during the rainy season or the dry season are the keys to help farmed shrimp overcome this. disease and good growth.
Some stress management solutions with high nutritional food, containing many groups of anti-stress nutrients
At present, most shrimp farmers in canvas ponds stock shrimps (shrimp sows) at a high density of 1,000 – 5,000 shrimp/m2, so the nature of nursery ponds at the farm is almost like rearing shrimp. In addition, shrimp larvae at the farm are fed with high-quality seed feeds (50%-60% protein) containing a lot of imported fish meal, squid meal, krill meal, seaweed meal and algae extracts and other nutrients. Fermented protein raw materials contain many biological peptides (biopeptides) that are anti-stress and antibacterial, and additives containing many antioxidant nutrients and anti-stress substances (carotenoids, Vitamins E, C, D3, A, nucleotides, beta- glucan, taurine, glutamine, Methionine, Sorbitol…). Studies by the Taiwan Biotechnology Company (Sciencechain Biotechnology Ltd.) also confirm that special groups of biological peptides (named Bacteriocins) can eliminate EHP microspores and protein sources. MOTIV yeast containing many bio-peptides is also starting to be of interest to shrimp feed companies.
Therefore, hatcheries on farms should have access to quality forages of the same quality as hatchery feeds, with high protein content, anti-stress nutrition as well as a source of feed produced in pellets. small by extrusion technology with less water pollution… Currently, there are a number of corporations on the market such as Cargill & Biomar has a rich feed source with extrusion technology in pellets from sizes 300 – 1,000 µm (0.3 – 1 mm) and rich in protein (50% protein), rich in anti-stress and antioxidant nutrients… Pellet extrusion technology not only makes pond water and shrimp ponds less dirty, but also makes the pellets easier to digest with vitamins and enzymes, and with high protein and anti-stress nutrients, will help shrimp grow. good health, good health and good resistance to stress and disease.
In addition, at the rearing stage after shrimp rearing, it is important to choose the right source of high-nutrient, anti-stress food, with biological peptides to slowly remove EHP spores to reduce the density of microspores. not enough to cause disease.
Along with the management of pond water environmental factors in the optimal range, it will help shrimp to be less stressed and easily overcome diseases, grow well with the lowest feed coefficient to make the farming more successful and profitable.
Manage water environmental factors in an optimal range so that shrimps are less stressed
As mentioned, pond water environmental factors must be managed in the optimal range including: dissolved oxygen (DO), pH, appropriate alkalinity and toxic gases Ammonia and Nitrite below the allowable level. Specifically: Dissolved oxygen: Minimum 6 mg/L in the sowing period and at least 5 mg/L in the post-sowing period; pH: 7.5 – 8 in the dry season or 7.8 – 8.3 in the rainy season; Alkalinity: 120 – 180 mg/L for the sowing period with little water change, at least 100 mg/L for the growing period in the dry season.
During the rainy season alkalinity should be at least 150 mg/L for both the sowing and rearing stages. Toxic Ammonia should manage total ammonia (TAN) < 1 mg/L if cultured pH 7.5 – 8 or TAN < 0.5 mg/L if cultured at pH 8 – 8.3.
Farmers should also note that the management of the above factors focuses on 1) Feed and feeding program; 2) Number of fans and oxygen tanks installed in the pond; 3) How to use lime and minerals to adjust pH and alkali are different in rainy season and dry season; 4) How to use artificial colors and probiotics to control algae and toxic gas in ponds in rainy and dry seasons.
In the dry season, farmers should focus more on controlling algae and DO content in the pond through awning, water level and some algae control tricks through fan, artificial colors and probiotics. In the rainy season, there are large fluctuations in environmental factors, especially salinity, pH and alkalinity, so controlling these three factors requires a combination of low-salinity food sources against stress and salt-increasing mineral sources. increased alkalinity: at the same time, it is necessary to develop a process to treat water sources and use minerals to increase salinity and alkalinity specifically for the rainy season to ensure the lowest fluctuations in salinity, pH and alkalinity.