Myxosporeans Chloromyxum cristatum, Chloromyxum fluviatile and Zschokkella nova (Myxozoa) are common gall bladder parasites of the cyprinid fishes frequently persisting as co-infections. Despite the fact that they are believed to be innocuous endocommensals, C. cristatum clearly displays the potential of a serious pathogen since it may pervade fish liver parenchyma and cause its necrosis. Employing the comparison of genetic distances among the myxosporean rDNA sequences and performing phylogenetic analyses, we demonstrate that cryptic species assemblages exist in C. fluviatile and Z. nova. Sequence comparison revealed that Chloromyxum legeri, previously assigned as a junior synonym of C. fluviatile, is a valid species. The same method is used to display the distinction of Z. nova isolates from China and the Czech Republic. We show that C. cristatum is not an assemblage of more species, and our results support the synonymy of Chloromyxum cyprini with C. cristatum. We have developed a multiplex PCR as an effective tool for the detection and discrimination of Z. nova, C. cristatum, and C. fluviatile. It is especially advantageous for the distinction of the non-mature plasmodia of both Chloromyxum species. This method also helped to assess the exact prevalence of these parasites in examined samples and enabled to select single-infected host samples for the intended population studies.

Institute of Parasitology Biology Centre Academy of Sciences of the Czech Republic Branišovská 31 370 05 České Budějovice Czech Republic

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