Statistically speaking, the sample taken should comprise 1 50 PL per tank (of 1 00,000or more PL) that are macerated together and a subsample taken for analysis. However,confidence can be increased if this sample is split into 5 groups that are analysedseparately to be 95% sure ofdetecting a 2% level of infection in the tank. The mannerin which these PL are taken will greatly affect the chances of a positive result. If thePL are taken from one place in the tank (perhaps where the strongest PL gather - asthe hatchery operator might like) the chances of finding positive animals is low. If 5samples of 30 animals each are taken from random sites in each tank and thencombined, the chances will be higher. Whilst if a large sample of PL are subjected tosalinity stress and 1 50 of the weakest PL taken for analysis (as perhaps the pondfarmer might prefer), the chances of finding any positive animals is greatly enhanced.
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