GAA introduces EMS web page with major solutions so far for EMS management

One of the most important documents is the GAA report on EMS called "Managing the Perfect Killer", which was the basis for the global EMS seminar they held in Vietnam in December.

Here are some of the highlights from that report.

GAA says that EMS was first detected in China in 2009. It moved to Vietnam in 2010, peninsular Malaysia in 2011, the northern part of the island of Borneo in 2011 and then Thailand in 2012. It jumped to Mexico in 2013. And we have news of a presumptive outbreak of EMS in India, but we are not aware of it being validated so far.

Although for the years 1990-2000, aquaculture production, including shrimp production, grew at a rate that would double volumes every ten years, since then, growth rates have fallen due to disease.  Major shrimp and salmon disease outbreaks have changed the picture for global aquaculture, and until these diseases are more successfully controlled, growth will be slower.

EMS has been shown to result from a bacteria that colonizes the stomach of the shrimp, and then releases a toxin that damages the hepatopancreas, preventing the shrimp from digesting its food, and then killing it through opportunisitic bacteria as it weakens.

The bacteria is a strain of Vibrio parahaemolyticus.  Vibrio is widespread in the water column naturally, and it appears that the concentration level is critical in determining whether EMS develops or not.

Further there will be a PCR rapid genetic test to confirm EMS that should be commercially available in the next couple of months. 

GAA listed some of the successful approaches done by various shrimp companies:

Agrobest found lower pH helped control algae blooms, which also helped to lessen EMS in their ponds in 2012.   They also found black tiger larvae were resistant to EMS, though not immune, but could not get enough disease free larvae to scale up production.

The CP Group had done a lot of work on EMS, and found several important lessons.

One is chlorination can actually worsen the problem.  If a pond is chlorinated, the vibrio bacteria bounces back more rapidly and outcompetes other bacteria making the situation worse.  The answer is that if disinfectants are used to clean a pond, the full microbial community has to be established using pro biotics before vibrio has an opportunity to outcompete.

CP also found a key fact- the Vibrio have a sense of density, and only release the toxin once they achieve critical numbers - so keeping that density down is a key hygenic factor.

CP has also found that salinity has a major impact, and in high salinity areas there may be whitespot, but no EMS; in brackish areas there will be EMS, and in low salinity areas - less than 5 parts per thousand, EMS does not appear. 

EMS is particularly a problem where a number of farms are using the same brackish river as a water source, and dumping bacteria loads into the river. 

Another factor seems to be bottom culture.  The Vibrio bacteria is "sticky" and appears to be concentrated on the bottom.  So when shrimp are first introduced to a pond - keeping them off the bottom in cages, or growing them in raceways for a few weeks, will result in preventing EMS.  Larger shrimp are much more resistant, so if they can survive the earliest stages in the pond, they will have more success at lower mortality.

So GAA is suggesting 4 practical setps:

1) stock larger shrimp

2) use black tiger shrimp where available

3) use a poly culture of tilapia and shrimp - this apparently creates a favorable bacteria environment and inhibits the vibrio that produces EMS

4) Use intensive bio-secured systems- including on small ponds.  The key to a viable small farm is very fast growing shrimp, and this is being tried in China.

In short, EMS and Vibrio will continue to exist, like White Spot, and will have to be successfully managed for shrimp production to resume its former growth rate.

The good news is that with a series of proper management measures - farmers and major growers like CP, are able to begin producing reliably again.