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While studying Myxobolus gill infections of cyprinid fishes, the authors found large, segmented plasmodia in three species: ide (Leuciscus idus), asp (Aspius aspius) and white bream (Blicca bjoerkna). As regards their size and morphology, the spores from these plasmodia corresponded to those of M. dujardini described from chub (Leuciscus cephalus). However, the 18S rDNA sequences of spores from the three cyprinids differed from those of M. dujardini. Based on molecular differences, this paper describes two new species: M. alvarezae sp. nov. from ide and asp, and M. sitjae sp. nov. from white bream. The two new species and M. dujardini had a similar tissue tropism, and infected the multilayered epithelium of the gill filaments. Histological examination of the infected filaments demonstrated that the large plasmodia with multiple buddings were formed from amalgamating small plasmodia. Besides carrying infection in the filamental epithelium, the three above fish species were infected by small intralamellar plasmodia as well. These plasmodia were filled by spores that resembled the roach parasite M. intimus both in morphology and seasonal development. The 18S rDNA sequences of ‘intimus-like’ spores from ide and asp differed only in some base pairs from spores found in the type host roach, and were identified as belonging to M. intimus. The spores found in white bream, however, showed 3.6-5.0% difference in DNA sequence from those of M. intimus; therefore, they have been described as M. eirasianus sp. nov. The aim of this paper was to demonstrate the importance of using molecular methods for separating and identifying morphologically corresponding or closely similar Myxobolus spp.
Of the 850 known Myxobolus spp., 89 named species have DNA (in most cases 18S rDNA) sequences deposited in the Genbank. Only a part of the deposited sequences represent well identified samples collected from adequate organs of the original hosts. Some of the samples were collected from additional hosts or from fishes genetically far standing from the type-host. In the paper, reliability of sequences of some best known Myxobolus spp., deposited in the Genbank from freshwater fishes of Eurasia’s Palaearctic Region, are surveyed. Genbank sequences are classified into three groups. Sequences obtained from morphologically well characterised Myxobolus spp., which were collected from the type hosts, compose the group of valid sequences. To the group of probable valid sequences belong samples from spores morphologically corresponding to the original description, but collected from fishes closely related to the type-host; while sequences obtained from hosts genetically far standing from the type-hosts represent the category of the un-valid group.
An overview on the myxosporean species infecting amphibians and reptiles is presented. The characteristics of the species are reported, as well as the pathology, hosts and geographical range. The host specificity and life cycle are discussed on the basis of the data thus far.
During a survey on myxosporean parasites of cyprinid fishes in Hungary, Myxobolus infections were found in the cartilaginous rays of the gill filaments in roach (Rutilus rutilus) and bleak (Alburnus alburnus). Myxobolus spp. causing the infections were studied by morphological, histological and molecular methods. Small plasmodia surrounded by chondrocytes contained relatively few spores which differed from each other and from the known Myxobolus spp. both in their morphology and 18S rDNA sequences. Both species, described as M. feisti sp. nov. and M. susanlimae sp. nov., are characterised by a specific cartilaginous histotropism.
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