Tetrahymena pyriformis infection in the tiger barb, Puntius tetrazona: Parasite characterization and pathology of infected fish

Abstract Tetrahymena pyriformis is a histophagus protozoan ciliate responsible for tetrahymenosis in various aquatic organisms including the tiger barb Puntius tetrazona. The morphology, infraciliature, SSU rRNA and cox 1 gene sequences of T. pyriformis isolated from P. tetrazona from a fish market in Harbin was investigated using living observation and silver staining methods. In addition, an SSU-rDNA-targeted oligonucleotide probe labelled with a fluorochrome was designed for rapid identification of T. pyriformis. Diseased fish secreted copious amounts of mucus on the skin and had dark-red spots in the eyes and at the base of tail fins. Gills of all diseased fish were shriveled and pale. T. pyriformis could be directly found when examined histologically by hematoxylin-eosin staining. The results showed that some T. pyriformis cells were present on the surface of the gill filaments. There was also abnormal bunting of the abdomen, and the gill filaments and muscle tissue were deformed, shrunken, and cracked. Successful infection of P. tetrazona was achieved with T. pyriformis by scratch inoculation with a range of infectious doses. The results indicate that T. pyriformis invades P. tetrazona through lesions on the body surface, and a large infectious dose could accelerate the death of the infected fish.