Molecular markers for gyrodactylids (Gyrodactylidae: Monogenea) from five fish families (Teleostei).

Thirty-one gyrodactylid species from five families of freshwater fish were examined and variable region V4 of the 18S small subunit ribosomal RNA gene and ribosomal RNA internal transcribed spacers ITS1 and ITS2 were sequenced. Both the V4 region and spacers ITS1 and ITS2 proved useful for gyrodactylid diagnosis. Sequences of these fragments exhibited interspecific variations and allowed clear determination at the species level. In some cases, the length of the ITS1 PCR fragment provided useful genetic markers. Species that yielded a short ITS1 fragment also showed distinct groupings in ITS2 and V4 sequences that were markedly different to sequences from species that contain a long ITS1. Repetitive sequences located in the ITS1 of Gyrodactylus gobii and Gyrodactylus vimbi accounted for some of the variations in length of PCR products. There was no evidence for intraspecific variation within these regions and short tandem repeats were not found in the other species studied. The number of polymorphic and intraspecific variations in nucleic acid sequences was low, therefore these variations did not affect species determination of gyrodactylids. Minor differences in the sequences between Western and Eastern European populations were detected for Gyrodactylus salaris/Gyrodactylus thymalli, Gyrodactylus teuchis and Gyrodactylus truttae, but these do not affect species diagnosis based on ribosomal DNA sequence. These results confirm the utility of both variable region V4 and the ITS as molecular markers for Gyrodactylus species.