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November 25, 2013

United States

Missouri—Dr. George Chamberlain on EMS/AHPND

 

At the Global Aquaculture Alliance’s (GAA) GOAL 2013 meeting in Paris, France (October 2013), disease was identified as the primary challenge obstructing the growth of shrimp farming.  At the meeting, Dr. George Chamberlain, president of GAA, moderated a panel on health management that reviewed early mortality syndrome (EMS), also called acute hepatopancreatic necrosis disease (AHPND).

 

Panel-member Robins McIntosh, a senior vice president at CP Foods in Thailand, described EMS/AHPND as the "perfect killer" because it grows extremely fast and is a colonizer that adheres to surfaces.  The colony coordinates the release of a potent toxin through a process known as quorum sensing.  He said recovery from the disease in Thailand would be complicated and likely require two to three years.

 

During an informal breakout discussion following the panel, other helpful information about EMS emerged.  For example, the pathogen does not grow in freshwater or nearly freshwater with up to 3 parts per thousand (ppt) salinity, but its growth increases from 4 to 11 ppt salinity, above which growth is unaffected by salinity.

 

Unlike viral pathogens, EMS/AHPND, a bacterial pathogen, can grow in coastal waters and shrimp ponds outside the host.  This challenges conventional methods for water treatment.  Chlorination followed by addition of molasses or other nutrients has not been effective in controlling EMS/AHPND, perhaps because chlorination kills competing bacteria, and the addition of nutrients stimulates the growth of V. parahaemolyticus.  On the other hand, well water has yielded improved survival when compared to the use of surface water.  These results suggested a greater role for filtration and probiotics in competing with and excluding EMS/AHPND.

 

Although laboratory bioassays indicate that both Penaeus monodon and P. vannamei succumb to an infective dose of V. parahaemolyticus, field results indicate monodon usually don't die of EMS/AHPND in ponds.  This suggests the feeding behavior of monodon is different than that of vannamei, which reduces its exposure.  Polyculture studies with fish such as tilapia have reduced EMS mortality in shrimp.  This is thought to be caused by the blooms of Chlorella algae in tilapia ponds, which may disrupt the quorum sensing ability of V. parahaemolyticus.

 

Source: The Global Aquaculture Advocate (The Global Magazine for Farmed Seafood).  Editor, Darryl Jory (dejry2525@aol.com).  GOAL 2013 Review: Challenge Health Management/Program Focuses on “Perfect Killer” EMS.  George Chamberlain.  Volume 16, Issue 6, Page 14, November/December 2013.

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