Despite of this question, we still have to emphasize the screening of broodstocks and PLs is more important than grow-out pond.

In the grow-out pond, the purpose of WSSV screening is not to pick the infected animals away from the pond.  The main purposes are to confirm the cause of mortality, to know the severity of infection, to avoid mass mortality, and to decide when to harvest.  Thus, we need to know both of the infectious rate and infectious level both to evaluate the condition of the grow-out pond.  When the infectious level is too high, the epidemic is under progressing.  When the infectious rate is too high (but very low infectious level), any stress will be able to trigger off the epidemic.

For the first 2 months, there is no need to screen the grow-out pond under normal condition, unless the farmers want to confirm the causen of mortality.  After then, it will be very important to harvest before mass mortality happens.  We recommend screening each grow-out pond every two weeks.  The sampling scale should be at least 10 animals per time, excise one pleopod for each animal and combine all of the pleopods, then to process a single extraction and PCR.  If the diagnostic result is moderate or severe WSSV infected, the farmers had better harvest immediately.  Of course a confirmation test is required before harvesting.  If the diagnostic result is light or very light WSSV infected, a further screening will be required.  The farmer needs to re-sample another 10 animals and diagnose individually.  If there exist any moderate or severe infected animal, an immediate harvest will be required.  If there exist no moderate or severe infected animal within those 10 animals, there will be no immediate risk, however any environmental change might trigger off the epidemic.  It is important to compare the infectious level and infectious rate (percentage) with every diagnosis to understand the progress of the viral risk.

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