Diseases of different scales still break out every year. Judging from the existing control methods, the occurrence of diseases can not be completely eliminated, and only preventive measures can be taken, among which seedling selection is particularly important. The most suitable stocking size of Penaeus vannamei is the larva with a body length of 0.8cm~ 1.2cm. At this time, the morphology and activity state of shrimp larvae can be clearly observed with naked eyes, and the shrimp larvae with good quality should have the following characteristics:

(1) Shrimp seedlings are uniform in size, transparent in body color and strong in vitality.

(2) The tentacles of shrimp seedlings should be close together, the tip should be straight forward, the tail fan should be fully opened, and the abdomen should be longer.

(3) The surface of shrimp seedlings should be clean, free from parasites and damage.

(4) Shrimp stomach is full and orange-red, and the ratio of abdominal muscle width to intestinal width should be greater than 4: 1. (5) At rest, most shrimps are submerged, and when stimulated by the current, they are flooded. Viral diseases, such as white spot disease, yellow head disease (YHV) and virus strain (TSV), can easily cause huge losses to prawn farming, because there is no effective treatment for these diseases, and once prawn diseases break out, farmers will lose their blood. Therefore, it can only be solved from the source. The shrimp seedlings detected by PCR will not carry harmful viruses, which can effectively prevent viruses from being brought into the breeding ground by shrimp seedlings and greatly reduce the probability of viral diseases in breeding. Therefore, when farmers buy shrimp seedlings, they must carry out testing to reduce the risk of breeding.