A strain of T. danilewskyi isolated from Carassius auratus gibelio in Czechoslovakia was characterized morphologically and morphometrically. Its multiplication process in C. auratus is described. The 1st stage was the production of a new flagellum and this was followed by kinetoplast division. The new flagellum flipped posteriorly and along it new cytoplasm was produced. Following nuclear division, one of the nuclei migrated posteriorly past the 2 kinetoplasts. Body division occurred by transverse constriction at a point between the kinetoplasts.