Histopathology of Gill Lesions of Ayu Plecoglossus altivelis Clinically Diagnosed with ‘Boke’ Disease

We investigated the histopathological features of the gill lesions of diseased ayu Plecoglossus altivelis that had been diagnosed with ‘Boke’. The features were classified into three types: one characterized by atypical gill epithelial cells, one characterized by numerous long Gram-negative rods, and one characterized by both atypical gill epithelial cells and long rods. TEM revealed the presence of poxvirus-like virus in the atypical gill epithelial cells. Our results indicated that ‘Boke’ was composed of different kinds of diseases. We propose ‘atypical cellular gill disease (ACGD)’ as the new name of novel gill disease in ayu.