Based on the data of water quality measured in the nursery ponds for one-year-old fingerlings of grass carp, the relationship between one or multiple water quality factors and viral hemorrhagic disease has been analyzed. The results, which were concluded by means of biological statistics, showed that breakout of the disease is closely related to some ecological factors. When water temperature rised gradually, the factors which were liable to the breakout and prevailing of the disease included increase of to...