Hemorrhagic Disease of Grass Carp: Status of Outbreaks, Diagnosis, Surveillance, and Research

Introduction Grass carp (Ctenopharyngodon idellus) is an important species of freshwater fish in China. It accounts for about 20% of the total freshwater fishery production. Hemorrhagic disease of grass carp is the most serious infectious disease of grass carp and causes significant losses of fingerlings during rearing. Survival to market size is less than 20% if this disease occurs. Hemorrhagic disease of grass carp was first discovered in a fish farm in Hubei Province in 1972. It was identified as of viral etiology in 1978 and became the first fish viral disease studied in China (Section of Virus Study, 1978). In 1980, virus particles in kidney sections of infected grass carp were observed by electron microscopy and the virus was tentatively designated a herpesvirus (Section of Virus Study, 1980). However, further study revealed that these were icosahedral particles with double capsids, no envelope, containing 11 segments of doublestranded RNA (Chen and Jiang, 1984). It was similar to some reoviruses isolated from aquatic animals, such as chum salmon reovirus (CSV), catfish reovirus (CRV), and golden shiner virus (GSV). Hence, it was classified as an aquareovirus and renamed grass carp reovirus (GCRV) in 1984. Hemorrhagic Disease of Grass Carp: Status of Outbreaks, Diagnosis, Surveillance, and Research