Molecular markers for gyrodactylids (Gyrodactylidae : Monogenea) from fivefish 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 sequence d. Both the V4 region and spacers ITS1 and ITS2 proved useful for gyrodacty lid diagnosis. Sequences of these fragments exhibited interspecific variati ons and allowed clear determination at the species level. In some cases, th e length of the ITS1 PCR fragment provided useful genetic markers. Species that yielded a short ITS1 fragment also showed distinct groupings in ITS:! and V4 sequences that were markedly different to sequences from species tha t contain a long ITS1. Repetitive sequences located in the ITS1 of Gyrodact ylus gobii and Gyrodactylus vimbi accounted for some of the variations in l ength of PCR products. There was no evidence for intraspecific variation wi thin these regions and short tandem repeat; were not found in the other spe cies studied. The number of polymorphic and intraspecific variations in nuc leic acid sequences was low, therefore these variations did not affect spec ies determination of gyrodactylids. Minor differences in the sequences betw een Western and Eastern European populations were detected for Gyrodactylus salaris/Gyrodactylus thymalli, Gyrodactylus teuchis and Gyrodactylus trutt ae, but these do not affect species diagnosis based on ribosomal DNA sequen ce. These results confirm the utility of both variable region V3 and the IT S as molecular markers for Gyrodactylus species. (C) 2001 Published by Else vier Science Ltd. on behalf of Australian Society for Parasitology Inc.