Establishment of a rare minnow (Gobiocypris rarus) disease model for grass carp reovirus genotype II

Grass carp haemorrhagic disease (GCHD) is one of the most important diseases affecting grass carp aquaculture. The rare minnow (Gobiocypris rarus) is a small experimental fish that has been proven to be sensitive to GCRV infection. However, few studies have definitively shown that rare minnow can be used as a disease model for GCRV-II, a recently emerging dominant genotype. In the present study, we investigated clinical characteristics, tissue tropism, histopathology, and relative expression of immune-related genes in rare minnow infected with GCRV-II virulent strain HuNan1307. Hemorrhage of rare minnow was induced by the GCRV-II, which could proliferate in the fishes, and the viral load peaked on the day 7. The histopathologic changes in rare minnow were primarily vasodilation and hyperaemia in multiple organs, cell degeneration and necrosis, as well as loose intercellular in spleen, kidney, brain and heart. Electron microscopic observation in the kidney revealed virus similar in shape and size to those GCRV-II infections in grass carp. Genes encoding IL-8, Mx, TLR5, IgM and IFNα were relatively high up-regulated in different tissues, while multiple genes in liver and spleen were significantly up-regulated, which was consistent with GCRV-II infection in grass carp (P < 0.05). Our study suggested that rare minnow can be used as a disease model of GCRV-II as a tool to study pathogenesis and develop vaccine against GCRV-II.