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What's the best organ of adult shrimps for WSSV diagnosis?

The white spot virus exists in most of the shrimp tissues, but three factors were considered when choosing the target tissue:

1. Tissues which contain more viruses than the others.

2. Tissues which are easier for sampling.

3. Tissues which are less harmful to shrimps. 

Therefore, we usually select pleopods ,gills, hemolymph, or periopods for diagnosis. Personally, I prefer the first two. It is easier to cut the pleopod and it contains less PCR inhibitors. But the gills might be the next trend as the target for viral diseases detection, because it is less harmful and also good for several other viruses diagnosis, such as YHV/GAV, IHHNV, and TSV.

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What's the best period for brooder diagnosis?

The best timing to check brooders by PCR is immediately after spawning. First, you can save the diagnostic cost. It is meaningless to check the brooders which can not spawn, and they were mostly severely infected.

Second, the correlation between the PCR negative eggs and PCR negative brooders after spawning is very high. If you only choose the PCR negative brooders after spawning and use their eggs, you will be able to greatly reduce the risk to introduce the white spot virus into your hatchery. We have known that the stress factors such as weather changing or bad water quality could trigger white spot virus to replicate, and spawning is also a very big stress for broodstock. If a brooder remains PCR negative after spawning, then white spot free is certain.

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How many PLs should we sample to reach enough confidence level?

150. Most of researchers agree on this number. If you aim to reach 95% confidence level in a very big population, for example more than 150,000 animals, it is really a magic number. But don't extract those 150 animals together, because the dilution factor will be too big to shadow potential positive result. Instead, we recommend separating those 150 animals into 5 groups for diagnosis.

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In the gow-out pond monitoring, how often should we do the diagnosis? How many shrimps should we take while sampling?

Some challenge procedures such as formalin treatment are widely used in PLs sampling. Basically, choosing smaller and weaker animals are the main concept while sampling.

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