Insights into the diversity,distribution and phylogeny of three ergasilid copepods (Hexanauplia: Ergasilidae) in lentic water bodies of the Morava river basin,Czech Republic

Ergasilidae are a globally distributed group of copepods parasitising fish. Despite their common occurrence in European freshwaters, there is relatively little molecular data available. In this study, we recorded three ergasilid copepod species parasitising six fish species (families Cyprinidae, Percidae, Centrarchidae) in lentic water bodies along the River Morava in the Czech Republic: Ergasilus sieboldi infecting fish gills, Paraergasilus longidigitus infecting nasal cavities and Neoergasilus japonicus infecting fins. This represents a further occurrence of N. japonicus as a non-native European species, and the first report of P. longidigitusis from Central Europe waters. While strong niche selection potentially offers a free niche for each of these ergasilids in all hosts, parasite co-infections were relatively rare, with species distribution among hosts reflecting host preference. This study provides the first molecular data for E. sieboldi and P. longidigitus as native European ergasilid copepods. Phylogenetic analysis based on combined 18S and 28S rDNA showed a close relationship between P. longidigitus with other Paraergasilus species, supporting a monophyletic origin of this genus. The phylogenetic position of E. sieboldi was not clearly resolved, highlighting the need for more data and further intensive genetic investigations of other ergasilid species.