Comparison of the Myxobolus fauna of common barbel from Hungary and Iberian barbel from Portugal.

We compared Myxobolus infection of common barbel Barbus barbus from the Danube River in Hungary with that in Iberian barbel Luciobarbus bocagei from the Este River in Portugal. In Hungary, we recorded 5 known Myxobolus species (M. branchialis, M. caudatus, M. musculi, M. squamae, and M. tauricus) and described M. branchilateralis sp. n. In Portugal we recorded 6 Myxobolus species (M. branchialis, M. branchilateralis sp. n., M. cutanei, M. musculi, M. pfeifferi, and M. tauricus). Species found in the 2 habitats had similar spore morphology and only slight differences were observed in spore shape or measurements. All species showed a specific tissue tropism and had a definite site selection. M. branchialis was recorded from the lamellae of the gills, large plasmodia of M. branchilateralis sp. n. developed at both sides of hemibranchia, M. squamae infected the scales, plasmodia of M. caudatus infected the scales and the fins, and M. tauricus were found in the fins and pin bones. In the muscle, 3 species, M. musculi, M. pfeifferi and M. tauricus were found; however they were found in distinct locations. Plasmodia of M. musculi developed intracellularly in muscle cells, plasmodia of M. tauricus were found in the dense connective tissue of the pin bones, whereas M. pfeifferi formed plasmodia in the connective tissue of the intramuscular septa. This latter species was often found in the cartilaginous gill arch as well. Comparative morphological and phylogenetic studies, as well as 18S rDNA sequences, revealed differences between the Myxobolus fauna of the 2 barbel species originating from different geographic regions.