Identification and infection mechanism of Tetrahymena vorax affecting the goldfish Carassius auratus

Tetrahymena vorax is the ciliate responsible for tetrahymenosis in the goldfish Carassius auratus. The morphology of parasitic Tetrahymena vorax isolated from C. auratus from an ornamental-fish market in Harbin was studied using living observation and silver staining methods. Carassius auratus had large, white or grey skin lesions located on various parts of the body but were most common laterally. Gills of all diseased fish were shrivelled, dark and had white ulceration. The eyes of several diseased fish had turned grey and their fins were damaged or partially blackened. Histopathological examination revealed a systemic infection, pathological features of C. auratus include presence of large, white or grey skin lesions, dark shrivelled gills, grey eyes, damaged and/or partially blackened fins and invasion of ciliate cells in epidermis and dermis, viscera and abdominal cavity. Successful systemic infection of C. auratus was achieved with T. vorax by three tested modes (scratch, immersion and injection). The results indicated that T. vorax invade C. auratus through lesions of the body surface of injured specimens.