The emerging disease early mortality syndrome (EMS) has caused large losses among shrimp farmers in China, Vietnam, Malaysia and Thailand. Causing mass mortalities, its spread points to the need for increased awareness and cooperative reporting, writes Eduardo M. Leaño, Network of Aquaculture Centres in Asia-Pacific. Taken from the Global Aquaculture Advocate, a Global Aquaculture Alliance publication.

The Asia-Pacific region, the top producer of aquaculture products in the world, is continuously beset by emerging aquatic animal disease problems that can cause high mortalities and economic losses among small farmers as well as commercial producers. Over the last couple of decades, diseases such as white spot syndrome, yellowhead disease and Taura syndrome heavily impacted shrimp aquaculture in the region and caused the collapse of the Penaeus monodon industry.

More recently, an emerging disease known as early mortality syndrome (EMS) – also termed acute hepatopancreatic necrosis syndrome or AHPNS – caused significant losses among shrimp farmers in China, Vietnam and Malaysia. It also reportedly affected shrimp in the eastern Gulf of Thailand this year (Flegel, 2012).

EMS affects both P. monodon and Litopenaeus vannamei and is characterized by mass mortalities during the first 20 to 30 days of culture in growout ponds. Clinical signs of the disease include slow growth, corkscrew swimming, loose shells and pale coloration. Affected shrimp consistently show abnormal shrunken, small, swollen or discolored hepatopancreases.

In China, the occurrence of EMS in 2009 was initially ignored by most farmers. But in 2011, outbreaks became more serious, especially at farms with more than five years of culture history and those close to the sea using very saline water. Shrimp farming in Hainan, Guangdong, Fujian and Guangxi suffered almost 80% losses during the first half of 2011 (Panakorn, 2012).

In Vietnam, the disease has been observed since 2010, but the most widespread devastation due to EMS has been reported since March 2011 in the Mekong Delta in southern Vietnam. EMS affects the main shrimp production areas of Tien Gang, Ben Tre, Kien Giang, Soc Trang, Bac Lieu and Ca Mau provinces, and a total shrimp pond area of around 98,000 ha.

In June 2011, unprecedented losses were reported for 11,000 ha of P. monodon farms in Bac Lieu. Some 330 million shrimp died in Tra Vinh, and 20,000 ha in Soc Trang suffered huge losses this year (Mooney, 2012).

In Malaysia, EMS was first reported in mid-2010 in the east coast states of Pahang and Johor. The outbreaks of EMS resulted in a drop in L. vannamei production from 70,000 mt in 2010 to 40,000 mt in 2011. Poor production is expected for 2012 with unconfirmed reports of EMS in the states of Sabah and Sarawak.

So far, no potential causative pathogen has been found for EMS. Possible etiologies include biotic or abiotic toxins, bacteria and viruses. Nonetheless, the spread of the disease and its devastating effects on the shrimp industries of the countries affected point to the need for contingency planning in other countries in the region, especially those that practice L. vannamei culture.

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