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Running mortality syndrome (RMS) is named by shrimp farmers for continuous low-level mortalities during the culture period, resulting in low survival and productions. The syndrome is widely prevalent in the vannamei farms since 2011 in Andhra Pradesh and Tamil Nadu. The affected shrimp show patches of whitish musculature in the junctions of 2nd and 4th abdominal segments as a clinical sign with continuous low-level mortalities. This condition results a small percent shrimp mortality in the affected pond on daily basis. As the mortality continues on daily basis till the rest of the culture period, it is called as “Running Mortality Syndrome (RMS)”. Usually the RMS started after 35–40 days of culture (DOC) with low mortalities and as the culture progressed, the mortality rate also increased and the problem becoming acute at around 90 DOC and the farmers were forced to prematurely harvest the crops.
Shrimp from RMS affected ponds tested negative for all the major OIE listed and other pathogens such as White Spot Syndrome Virus (WSSV), Infectious Hypodermal and Hematopoietic Necrosis Virus (IHHNV), Monodon Baculovirus (MBV), Hepatopancreatic Parvo Virus (HPV), Infectious Myonecrosis (IMNV), Taura Syndrome Virus (TSV), Yellow Head Virus (YHV), and Penaeus vannamei Noda Virus (PvNV).
Causes:
Bacteriological examination of haemolymph and hepatopancreas samples of RMS affected shrimp indicated predominance of Vibrio spp., such as Vibrio parahaemolyticus and Vibrio azureus.
Symptoms:
In early stages of this condition, Litopenaeus vannamei, show certain gross symptoms. These include:
Management:
Running Mortality Syndrome is depicted be pond management associated syndrome rather than infectious in nature and thus can be overcome through best management practices.
In the beginning days, farmers managed this disease by regularly removing the dead shrimp from the pond. Reducing the stocking density by partial harvesting reduced the mortality. Reduced feed quantity or suspending feed for few days reduce the mortality.
The culture practices like stocking bigger post larvae, Avoid over stocking, nursery management, Regularly monitor water quality, health of animals, strict feed management and partial harvest will reduce the incidence of RMS.
Treatment:
During the onset of Running Mortality, very few dead pieces were found in the pond, a very much advised of V Phages Growout to control Vibrio sp. in the pond. It helps to drastically reduce the Running Mortality Syndrome. It is always advised to apply Bacteriophages as a preventive strategy to avoid RMS conditions caused by Vibriosis.
Acute hepatopancreatic necrosis disease (AHPND) earlier known as early mortality syndrome (EMS) or acute hepatopancreatic necrosis syndrome (AHPNS) has been causing significant losses in shrimp farms in China, Vietnam, Malaysia, and Thailand since 2009. The disease affects both black tiger shrimp and Pacific white shrimp and is characterized by mass mortalities during the first 20-30 days of stocking.
Research by the University of Arizona has identified that the disease is caused by the bacterial agent Vibrio parahaemolyticus, which is transmitted orally and colonizes the shrimp’s gastrointestinal tract. This then produces a toxin that causes tissue destruction and dysfunction of the shrimp digestive organ known as the hepatopancreas.
Causes
The disease is caused by a unique strain of Vibrio parahaemolyticus, which can produce toxins responsible for the primary pathology in affected shrimp. Other non-Parahaemolyticus strains such as V. campbellii, V. harveyi, V. owensii, and V. punensis are also found to contain the same toxic genes and may also cause the disease.
Symptoms
Management
Bacterial infections of farmed shrimp are quite common and likely the major cause of mortality in farmed shrimp. Vibriosis is one of the most severe bacterial diseases in shrimp farming caused by Vibrio spp. These bacteria from part of the natural microbiota of wild and cultured shrimp and the marine environments. Vibrio infections have become a major constraint of the production and trade in shrimp aquaculture. They are responsible for several diseases and mortalities of up to 100% and cause crop loses globally.
Vibrio usually associated with multiple etiological agents. Vibrio has been reported in penaeid shrimp culture systems implicating at least 14 species and they are Vibrio harveyi, V. splendidus, V. parahaemolyticus,V. alginolyticus, V. anguillarum, V. vulnificus, V. campbelli, V. fischeri, V.damsella, V. pelagicus, V. orientalis, V. ordalii, V. mediterrani, V. logei etc. However some Vibrio species have been identified as primary pathogen, including V. parahaemolyticus and V. harveyi have been described as the main pathogenic species in shrimp.
Clinical signs of Vibriosis
Shrimp diseases associated with Vibriosis
Vibrio can remain in the environment without causing disease, but can very easily switch from opportunistic and commensal to pathogenic when conditions change. Thus, its ability to cause disease or increase in virulence, is a complex process affected by many variables, including host, vibrio species, developmental stage, physiological conditions, environmental stress, and infection method.
They are several diseases associated with Vibriosis.
Diagnosis
Diagnosis of vibrio infection is based on clinical signs and the histological demonstration of rod-shaped Vibrio bacteria in lesions, nodules or haemolymph. Excised organs and haemolymph may be streaked on a Vibrio-selective (TCBS) or general marine agar plate. Vibrio isolates may be identified by a number of methods, including: Gram stain, motility, an oxidase test, mode of glucose utilisation, growth in the presence of NaCl, nitrate reduction and luminescence.
Vibrio threshold in shrimp farms:
There are many vibrios maximum threshold standards in farms. Most of them are for Vibrio spp. in pond water. These are the common maximum thresholds used by shrimp farms:
How to prevent Vibrio problems?
Vibrios are difficult to eradicate because they adopt well to different environment conditions and can adopt state when facing adverse conditions. However, Vibriosis is controlled by rigorous water management and sanitation to prevent the entry of vibrios in the culture water and to reduce stress on the shrimps. Pond Management and robust gut health are important strategies to control vibrio, together with frequent sampling to monitor their levels in the shrimp gut and pond ecosystem.
Good site selection, pond design and pond preparation are also important. Maintain adequate water quality with low bacterial biomass, A stable phytoplankton bloom and a proper feeding program, Sterilize or filter recirculated water, Routinely monitor shrimp and pond for early diagnosis of a problem, Avoid temperature extremes or rapid variation in temperature, handling, overcrowding, and other stressors, Infections opportunistic and probably result from poor husbandry; may be secondary to other disease processes. An increase in daily water exchanges and a reduction in pond biomass by partial harvesting are recommended to reduce mortalities caused by vibriosis.
The combination of gut acidifiers, prebiotics, use of natural antimicrobials and Probiotics, Bacteriophage applications, immunostimulants and non-antibiotic substances has superior specificity against vibriosis and Luminescent Bacteria (LB) coupled with Best Aquaculture Practices (BAP) , which makes it an effective management tool for the control of vibriosis and bacterial toxicity in aquaculture.
Treatment
Use V Phages Growout immediately when various symptoms of Vibriosis as Luminescence in water, infections in shrimp and or low feed intake etc., correlated by lab test.