SEAFOODNEWS.COM by John Sackton — October 8, 2013 — The 13th Global Aquaculture Alliance GOAL meeting opened in Ho Chi Minh City, Vietnam Wednesday morning, with a series of impressive presentations about shrimp.
One of the hallmarks of GAA is that it is a very active organization involved in promoting global aquaculture. As a result, they have been at the forefront of efforts to understand and then address the EMS virus, which has devastated the global shrimp industry.
The good news from the conference is that shrimp production will increase again in 2015, and that there are signs of progress in containing and managing EMS. In his keynote speech, GAA president George Chamberlain said “the battle against EMS is now shifting from guessing what to do to implementing what works. ”
But, disease management is an ongoing issue for the shrimp industry, and even as EMS is understood and brought under control, new diseases and parasites are emerging.
For this reason, GAA is adding zone management to its BAP certification scheme. This will mean a fifth star in their system, covering hatcheries, feed, farm, processing plant, and now zone.
The Zone management standard will apply when a group of farmers within the same area has agreed collectively to take a series of actions that will prevent the spread of disease from one farm to another. It is a technique that will prevent the poor response of a single farm from creating disease problems for other farms in the area.
News from the meeting included first, a projection that global shrimp production will increase at a rate of 7.9% per year between 2013 and 2016. However, this has come after a 19% drop in global production from 2012 to 2013 due to EMS.
The shortfall, or opportunity cost of lost production during these years – 2013 to 2016, has been 3 million metric tons of shrimp, or around six times what the US imports each year.
A panel outlined how EMS has been brought under control.
First, of course, came the standard description of the disease, i.e. what was EMS. In 2013, Dr. Lightner discovered the cause – a strain of Vibrio parahaemolyticus, a common bacterim, that developed a toxin in shrimp.
Vibrio is an ubiquitous bacteria, and initial testing gave a number of false positives. However, it was discovered that the toxin was the result of a plasmid, and that there were two specific proteins in the toxin that could serve as reliable markers for standard pcr analysis.
So a 100% reliable and quick test to determine whether EMS was present was developed and made freely available in June of this year.
AT the same time, GAA, supported by the World Bank and the Seafood Industry Research Council, launched a survey of farms hit with EMS and got responses from more than 1,000 farmers. They then analyzed the survey to try and understand which practices seemed to be associated with reduced losses from EMS.
The survey found that 90% of farmers responding had experienced EMS losses. The modeling of the data showed that it was the individual characteristics of the shrimp itself that was most important. The survey uncovered some genetically resistant strains of shrimp in Mexico, and these appeared to have the highest survival.
These results are very preliminary, and it is still one to two years before the resistant genetic strains could be incorporated into brood stock, and that specific pathogen free, or specific pathogen resistant post larvae are available.
However, widespread adoption of an improved breeding stock, bred for resistance to a disease, has been used successfully in the shrimp industry to overcome things like Taura syndrome. It appears that over time, shrimp broodstock can become more resistant to EMS as well.
But that is not sufficient. In addition there are a number of other improvements needed to get survival rates high again.
They include:
-surveillance with PCR test for broodstock and post larvae prior to stocking ponds
-breeding for genetic resistance
-improving biosecure hatchery techniques (this was a major area of transmission)
-implementing strict management of ponds
-using feed additives that can assist in combatting EMS.
The story of how EMS started has begun to come out. It initially developed in China, and was allowed to exist for a couple of years without a serious response. Because it is a bacterim, not a virus, it does not need a host organism, but can be eliminated if its spores are destroyed. On the other hand, it easily gets into carrier organisms that feed on infected pond bottoms.
One of the transmission vectors out of China was polychete worms that are used throughout hatcheries in Asia because feeding broodstock live worms doubles their egg production. Many of these worms were bought from China. As a result, hatcheries were introducing EMS pathogen through the feeding methods of their brood stock.
So control and testing of broodstock and post larvae will become an essential prevention mechanism.
However, Chamberlain also said new diseases are already appearing. One is a parasite that causes slow growth, and is already widespread in China and Thailand. This parasite is too small to be seen in typical blood laboratory slides, but once a test is developed, it is possible to control it.
Several others speakers talked about other measures, including polyculture with tilapia, and the importance of managing the bacterial load in the pond.
When the proper bacteria balance is present, the EMS pathogen does not get a chance to grow in any quantity. Tilapia helps by moderating the natural bacteria and algae present.
Other methods that help maintain a good bacteria mix are the use of pro-biotics.
Antibiotics make EMS worse. By killing all the “good” bacteria in a pond, if EMS is present it will then expand with little competition. Normal draining of the pond and disinfecting does not work, as the resulting bacterial environment is out of balance and EMS can thrive if it is reintroduced.
For the bigger picture, success in developing an EMS resistant shrimp, plus pond management techniques and testing, will allow global farmed shrimp production to regain its high growth rate. By 2016, global shrimp production will have recovered to its 2012 peak of around 4 million metric tons annually. After that, continued growth will lead to 8 million tons of shrimp annually by 2024, as improved genetics, pond management, and hatchery management are implemented.
That is good news for the long term future of one of the most important farmed seafood commodities.
This story originally appeared on SeafoodNews.com, a subscription site. It has been reprinted with permission.