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August 28, 2013
Missouri—Video—Dr. George Chamberlain on EMS
In this 15-minute video produced by SeafoodSourceTV, online editor Sean Murphy talks with Dr. George Chamberlain, president of the Global Aquaculture Alliance, about early mortality syndrome (EMS), the disease that is decimating shrimp farms in Vietnam, Malaysia, Mexico and Thailand.
Sean Murphy: Its proper name is “acute hepatopancreatic syndrome” (AHPNS), but it’s easier to say its common name “early mortality syndrome” (EMS). It’s been running rampant on shrimp farms in Southeast Asia since 2009. New research, however, pins the cause of the disease on an infected form of the Vibrio parahaemolyticus bacteria. Other research from Kinki University and the National Institute of Aquaculture in Japan suggests a cure for EMS, or at least a treatment. Lowering the pH in shrimp ponds could drive out the bacteria and stop the disease. But is it really that simple and if so how, will this change the shrimp farming industry in Southeast Asia and beyond? Here to tell us about that and EMS is George Chamberlain, joining us today via Skype from GAA’s offices in St. Louis, Missouri, USA.
George, tell us about the research on balancing pH that your organization first told the world about. What is pH and how does it affect EMS?
George Chamberlain: Measured on a continuum from zero to fourteen, pH is the balance between acid and base. Seven is considered a neutral pH, neither acid nor base. Full-strength seawater normally has a pH of about 8.2. EMS is stimulated or triggered by a pH of around 8.5 or 8.8 and inhibited by a pH of less than 8, maybe even less than 7.5. This was discovered by a shrimp farm manager named Noriaki Akazawa who manages a shrimp farm in Malaysia called AgroBest, which is owned by the seafood trading company Maruha Nichiro Holdings, Inc. It’s a large farm with 460 ponds and it was producing about 11,000 metric tons of Penaeus vannamei shrimp a year. The farm kept good records and knew exactly when EMS hit. It came in with a batch of postlarvae from an outside hatchery. So, apparently, EMS is transmitted by infected postlarvae and probably by infected broodstock. The disease started in five ponds, all five of them stocked with postlarvae from the same hatchery. But other ponds were stocked with the same batch and did not break with the disease. That was the first clue that something unusual was going on.
Akazawa brought some moribund shrimp into his lab, put them in an aquarium and then ran back to the pond. When he returned to the lab, he expected to find that the shrimp had died, but they were perfectly fine, swimming around normally, and they stayed healthy for another week until he released them. Why were they dying in the pond and why did they recover when he put them in an aquarium. After looking at a lot of data, he discovered that the difference was pH. The ponds with the moribund shrimp were experiencing high pH, which encouraged the disease. The aquarium had a much lower pH and the disease regressed. So managing pH is one method for controlling the manifestation of EMS.
Sean Murphy: That seems like a tantalizingly simple solution to a billion-dollar-a-year problem. Is it really as simple as maintaining the proper pH?
George Chamberlain: First of all, I think it’s much more than a billion-dollar problem. I thinks it’s costing Vietnam a billion dollars a year, and it’s probably costing Thailand more than a billion dollars a year. If you add it all up, I think it’s a multibillion-dollar-a-year problem. But you’re right, it appears to be a simple solution, but managing pH is difficult because it’s affected by many factors in the pond, both biological and chemical. One of the main factors driving pH up is photosynthesis. The common denominator for pH in the pond is carbon dioxide. When carbon dioxide is dissolved in water, some of it forms carbonic acid, which lowers the pH. During daylight hours, however, the microalgae in the ponds photosynthesize, which means they absorb carbon dioxide and that increases the pH, which triggers EMS.
Another factor that affects pH is the bacteria in the pond. As bacteria metabolize organic matter in the pond, they produce carbon dioxide and that drives the pH down, so the more bacteria in the water the lower the pH will be. We know that some intensive shrimp farms encourage bioflocs and that these farms tend to have consistently low pH levels, and they, anecdotally, report less trouble with EMS. So managing bacteria and algae is part of the solution for managing EMS. Although difficult to control, bacteria and algae can be brought into better control by not overfeeding or over fertilizing. Methods we used in the past, like stimulating a good phytoplankton bloom before stocking shrimp, may be counter productive and encourage EMS. Instead of taking two weeks to prepare a pond with a really rich phytoplankton bloom that supplies a lot of natural food, some farmers are stocking right away before they get a plankton bloom because they don’t want to expose the postlarvae to high pH.
But focusing only on pH is probably misleading. One of the biggest issues, I think, is contamination of the postlarvae with EMS at the hatchery level. If the farmer is stocking infected postlarvae, managing algae and bacteria to control pH may not help. The first step is to make sure that the broodstock going into the hatchery is free of EMS, that the hatchery keeps the postlarvae from those broodstock free of EMS and that the farm uses proper management to avoid high pH by keeping the nutrient levels under control.
Also, feed is likely to be part of the solution. This disease colonizes the stomach of the shrimp, so EMS could easily be influenced by feed. If the organism is affected by high pH, maybe it’s possible to modify the pH of the stomach by using additives in the feed. When you think about it, the entire production chain—breeding, hatching, farming and feeding—is part of the process. The solution to the problem is going to require an integrated approach involving the entire production chain. I think by controlling the entire production chain, we have a much better chance of controlling EMS. This is a little more difficult when we look at the Asian situation where most of the hatcheries and farms are run by very small operators. One of the indirect side effects of this disease is going to be more consolidation and integration in the industry, which was recently predicted by Rabobank in its report called “Shrimp in a Crimp” that basically said there’s a greater need for biosecurity in the Asian industry, which will lead to consolidation and integration, and I couldn’t agree more.
Sean Murphy: Do you think we’re going to be able to bring EMS in Southeast Asia under control quickly?
George Chamberlain: Unfortunately, I don’t see a silver bullet or an immediate cure. I think the management solution will be a comprehensive one. It’s going to require proper breeding, hatchery management and high-quality farm management. Many shrimp farm managers don’t even own a pH meter, and they don’t measure nutrient levels in their ponds or track bacterial levels. It will take a paradigm shift to get them to more carefully control their ponds. I don’t see an immediate solution. I think this is going to take a year or two, or maybe more, for a full recovery. I think it’s going to be a slow, steady process. Companies that take full control of the farming cycle will probably have the most success in controlling EMS.
From the very beginning of the farming cycle to the very end, it’s a question of biosecurity. Every few years, we see the impact of another shrimp disease. Inevitably the response is to tighten biosecurity, and as we do that, the industry is getting more and more consistent. The controls are helping to prevent other diseases. Over time, these controls also improve the environmental sustainability of the industry. There’s less water exchange and less transmission of disease.
Sean Murphy: George and many other people from the Global Aquaculture Alliance will be on hand at Goal 2013, the Global Aquaculture Alliance’s annual conference, which will take place in Paris, France, on October 7-10, 2013. You can be sure that Seafood Source TV is going to be there to provide full video and written coverage of everything at the conference. I’m sure that EMS will be discussed at the conference.
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