Morphological and molecular biological studies on intramuscular Myxobolus spp. of cyprinid fish

The validity of Myxobolus species infecting the skeletal muscles of six cyprinid fish species was studied by morphological and molecular biological methods. Intracellularly developing Myxobolus spores identified as M. cyprini from the common carp, M. musculi from the barbel, and M. pseudodispar from the roach, rudd, common bream and white bream were very similar in their shape and size. Nonetheless, in species identified as M. pseudodispar, the occurrence of spores with an asymmetrical shape was higher than in M. cyprini, while asymmetrical spores were only occasionally found in M. musculi. The DNA sequence analysis of the polymerase chain reaction (PCR)‐amplified 18S rRNA gene of Myxobolus spores from these fish showed a similar phylogeny to that of their host species. As morphological studies and DNA sequence analysis demonstrated slight but real differences in the spores infecting muscles of the six cyprinid species, it is suggested that M. musculi, M. pseudodispar and M. cyprini are valid species.