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Nelson Gerundo (email@example.com): Enterocytozoon hepatopenaei (EHP) is a microsporidian parasite that infects shrimp in outdoor ponds. Clean postlarvae pick up EHP soon after they are stocked in contaminated ponds. Subclinically infected postlarvae spread the disease to non-contaminated ponds.
Hatcheries can become contaminated with EHP, especially when they buy local, pond-reared broodstock derived from imported SPF/EHP-free broodstock. The best way to avoid hatchery contamination is to import EHP-free broodstock from reliable sources and avoid feeding that broodstock with locally caught live or fresh invertebrates (polychaetes, clams, mussels, crab meat, shrimp meat or lobster meat). Freeze those items to kill the spores, and then you can use them.
Better yet, do not buy locally grown broodstock or its postlarvae from hatcheries located within EHP endemic zones, especially when there are reports of shrimp not growing well, or dying, in those zones.
EHP is endemic in Thailand, Vietnam and India. If your shrimp farm is located in one of those countries and if you’re purchasing locally produced broodstock and postlarvae, you may be purchasing EHP infected animals.
• Never buy locally grown, pond-exposed broodstock from any hatchery, whether it is located in EHP problematic areas or not. Chances are that it’s subclinically infected.
• Never buy postlarvae from any hatchery that uses locally grown, pond-exposed broodstock.
• Buy your postlarvae from local hatcheries that use certified, EHP-free broodstock or imported broodstock from countries with no history of EHP.
• Always ask for an EHP health clearance certificate or some other valid proof that the postlarvae you are buying have been cleared for EHP by your government disease-testing laboratory before you even begin thinking about paying for those postlarvae.
• Before purchase, ask your hatchery for two small bags of postlarvae. Take them to your nearest government accredited shrimp disease testing center for EHP clearance.
• Always be in contact or collaboration with your government shrimp health authorities. They are there to serve and protect you and the shrimp industry.
Remember, if your shrimp farm is located in Thailand, Vietnam or India, the broodstock or postlarvae that you are buying locally may be infected with EHP.
Because subclinical infections are difficult to detect, hold some postlarvae samples in oxygenated plastic bags for two days or longer. The crowded conditions in the bags will bring on stress, weaken them and make them more likely to break with a subclinical disease. Re-oxygenated the bags daily, and then submit them to your government accredited shrimp disease testing center for EHP detection.
Buying animals that are from countries with no historical record of EHP means that those animals are highly likely to be susceptible to EHP infection. That concept has been field tested, and it doesn’t work. It’s the last thing I would suggest to anyone trying to manage EHP.
A better way is to buy from countries that have EHP and have a good SPR breeding program to build resistance to EHP. Results in Thailand and China strongly suggest that concept is working.
Government labs can be good sometimes and sometimes completely unreliable. I think people have to judge for themselves.
Certificates mean nothing in many shrimp farming countries. Anyone with a computer and inkjet printer can make a certificate.
Pond exposed broodstock can be a good starting point if they come from a good SPR breeding program. In fact, experience dictates that this is the strategy that’s most likely to bring EHP under control.
EHP is also endemic in China, and there are unconfirmed reports of it in Latin America.
Robins McIntosh, Senior Vice President of Charoen Pokphand Foods Public Company Limited, said EHP represents a bigger threat to shrimp industry than EMS because its very difficult to control once it gets established.
Many government PCR labs have such poor procedures that cross contamination causes false positives and false negatives.
My advice is not to place too much faith in government labs and certificates. First, find out how they do their testing, and then check their quality controls. If in doubt, consider purchasing a LAMP (Loop-Mediated Isothermal Amplification) or PCR (Polymerase Chain Reaction) kit and do it yourself.
In my recent experience, even PLs from famous, large-scale hatcheries with many well-qualified PHDs on staff are showing up positive for EHP. This is not an easy disease to manage and one must balance the academic issues with the empirical and practical issues.
A word of caution. Don’t believe everything you hear from seedstock salesmen. When in doubt, always ask for a second opinion. Ask your shrimp farmer’s association or your country’s official expert on shrimp disease for their opinions.
I am not an expert on Enterocytozoon hepatopenaei (EHP). Following is a list of EHP experts you might want to contact:
• Dr. Kallaya Sritunyalucksana (firstname.lastname@example.org), Shrimp Virus Interaction Laboratory, National Center for Genetic Engineering and Biotechnology Development Agency, Yothi Office, Rama VI Road, Bangkok 10400, Thailand.
• Dr. Siripong Thitamadee (email@example.com), Center Shrimp, 4th Floor, Chalermprakiat Building, Faculty of Science, Mahidol University, Salaya 73170, Thailand.
• Professor Timothy W. Flegel (firstname.lastname@example.org, Center Shrimp, 4th Floor, Chalermprakiat Building, Faculty of Science, Mahidol University, Salaya 73170, Thailand.
The focus of our current research is on feed as a stress factor that leads to disease. Feed formulations have changed dramatically in the last 10-15 years, and so have the number of problems in shrimp farming. Ingredients that contain phytochemicals and other factors that don’t harm terrestrial vertebrates may cause toxic reactions in shrimp.
Hector Rincon (email@example.com): What affect does low salinity, say around six parts per thousand (ppt), have on the aggressiveness of EMS and EHP. Has EMS ever caused mortalities or low survivals at salinities below 6-ppt? Do intracellular bacteria have salinity preferences? Do they like low salinities?
Nelson Gerundo (firstname.lastname@example.org): A word of caution, when you’re buying broodstock and seedstock, watch out for huskers, guys that may not tell the truth, or not even know the truth. When in doubt, always get a second opinion. Ask your shrimp farmer’s association about who’s good and who’s bad.
Daniel Gruenberg (email@example.com): Hector, bacterial growth rates may be a bit slower at lower salinities, but that doesn’t mean you’re protected from EHP or EMS. A large farm that I work with in Thailand is on a recirculating system. To fend off disease, they lowered salinities, but it didn’t help, so they stopped doing it.
Hector Rincon (firstname.lastname@example.org): Daniel, thanks for your opinion. Right now, in Venezuela, we are doing fine, with good survivals. It looks like it could be a good year. It would be nice if our growth rates were a little better.
What’s happening with Venezuela’s broodstock import ban that Gina Conroy promoted when EMS first showed up? It’s probably high time to replace the ban with strict quarantine procedures.
What are your current survival and growth rates?
Hector Rincon (email@example.com): Daniel, please contact me a few days before you arrive in Venezuela.
The import ban was lifted when the Taura virus hit us in 2005.
Right now, at 140 days, our survivals are 60% and, on average, the shrimp weigh 15 grams.
One of the surprising things about EHP is the absence of any external indicators of the disease on the shrimp’s body—no localized melanization, no swelling, no bumps, no discolorations, no specks and no abnormal cuticular spots.
Subclinically infected postlarvae look just like normal-bodied PLs. The disease expresses itself during growout with noticeably slower growth rates.
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