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.

Myxobolus erythrophthalmi sp. n. and Myxobolus shaharomae sp. n. (Myxozoa: Myxobolidae) from the internal organs of rudd, Scardinius erythrophthalmus (L.), and bleak, Alburnus alburnus (L.).

During a survey of myxosporean parasites of cyprinid fish in Hungary, infections caused by unknown Myxobolus spp. were found in the internal organs of rudd, Scardinius erythrophthalmus, and bleak, Alburnus alburnus. Small plasmodia developed in blood vessels of the kidney, liver, testes and intestinal wall. The parasites were studied on the basis of spore morphology and by histological and molecular methods. In most cases, plasmodia were surrounded by host tissue without a host reaction; however, in advanced cases, a connective tissue capsule was seen around plasmodia. Spores collected from the two fish species differed from each other and from the known Myxobolus spp. both in their morphology and 18S rDNA sequences. The two species, described as M. erythrophthalmi sp. n. from rudd and M. shaharomae sp. n. from bleak, are characterized by a specific histotropism to blood vessels, while the organ specificity involves the kidney and for the latter species, most internal organs.

Comparative morphological and molecular studies on Myxobolus spp. infecting chub from the river Danube, Hungary, and description of M. muellericus sp. n.

During a survey on fishes from the River Danube, the occurrence of 8 Myxobolus species (Myxozoa: Myxobolidae) was registered in chub Leuciscus cephalus L. Most species had a specific location within the fish host. M. cycloides was found in the wall of the swimbladder; the branched plasmodia of M. dujardini were located typically in the epithelium of the non-lamellar part of gill filaments; the plasmodia of M. ellipsoides infected fins between 2 fin rays; M. muelleri and Myxobolus sp. 2 formed large elongated plasmodia in the afferent gill artery of filaments, while the round cysts of M. muellericus sp. n. filled the capillary network of the gill lamellae. Intramuscular plasmodia of M. pseudodispar proved to be the most common, although large cysts of Myxobolus sp. 1 were also frequently found in the intestinal wall. Despite similarities of some species in spore morphology, 18S rDNA sequences showed clear differences between the species examined.