Abstract
The causal relationship of atypical cellular gill disease (ACGD) and Plecoglossus altivelis poxvirus-like virus (PaPV) in ayu Plecoglossus altivelis was studied through a transmission experiment in which naive fish were exposed to the filtrate of a homogenate of diseased fish gills containing PaPV. ACGD symptoms, including lethargy and abnormal swimming such as staying away from the water current with open opercula, were observed in the fish exposed to the virus at 4 days post-exposure (dpe) at 20°C. The cumulative mortality in the virus-exposed fish groups with and without sodium nifurstyrenate pretreatment was 82% and 56%, respectively. Dead fish showed atypical gill epithelial cells on gill filaments with PaPV DNA at 107–109 copies/mg level. In addition, fish were experimentally infected at different rearing temperatures of 18°C, 23°C and 28°C. Fish death was first observed at 15 and 10 dpe in the experimental groups at 18°C and 23°C, with cumulative mortality of 58% and 42%, respectively. However, there was no mortality in fish reared at 28°C. These results suggest that the etiological agent of ACGD in ayu is PaPV, and ACGD occurrence can be influenced by the rearing water temperature.
