3.1. The epidemic time and clinical symptoms of diseasedH. nipponia
Cultivation of H. nipponia is shown in Figure 1. The epidemic
time of H. nipponia was from May to October each year, when
temperature is between 25-35 ℃. Diseased H. nipponia obviously
showed reduced food intake, swam slowly and floated on the water. The
incidence and mortality rates of H. nipponia were very high,
causing serious economic damage to farmers. Only a small part of the
body surface of diseased H. nipponia was congested and most of
the body surface was normal without debonding (Figure 2). Internal
organs were found to be edematous and erosive.