Differentiation of Myxobolus spp. (Myxozoa: Myxobolidae) infecting roach (Rutilus rutilus) in Hungary.

During a survey on fishes from Hungarian freshwaters, the occurrence of eight Myxobolus species was registered in roach (Rutilus rutilus L.). Most species had a specific location within the fish host. Of the known species infecting roach, the intramuscularly developing species Myxobolus pseudodispar was found to be the most common. Besides Myxobolus intimus and Myxobolus diversicapsularis infecting the capillary network of gill lamellae, Myxobolus feisti infecting the cartilaginous gill rays were observed. Of the "muelleri-type" Myxobolus spp, Myxobolus rutili and Myxobolus sommervillae sp. n. formed elongated plasmodia in the gill filaments outside and inside the arteria efferens, respectively, while Myxobolus wootteni sp. n. developed cysts in fins. Plasmodia and spores of Myxobolus fundamentalis sp. n. were detected in the cartilaginous gill arch under the basis of gill filaments. Despite similarities of some species in spore morphology, 18S rDNA sequences and phylogenetic analyses showed clear differences among all species examined. The findings of the study demonstrate that morphologically similar spores could only be correctly identified by considering the location of plasmodia and the genetic characters of the myxozoan species.