First insights into the ectoparasitic helminth fauna of freshwater fish on an Adriatic island.

Surface flow of freshwater on Adriatic islands is rare due to the extreme permeability of the karst terrain. Hence, most helminthological studies of freshwater fishes in the Adriatic drainage have focused on mainland freshwater systems, while data from islands are scarce. We collected minnow, Phoxinus lumaireul (Schinz, 1840), specimens in the Suha Ričina stream on Krk Island and screened them for helminth ectoparasites. Identification of metacercariae cysts (black spots) was carried out by sequencing part of the 28S rDNA gene, and a single monogenean worm was identified by sequencing part of the internal transcribed spacer 2 (ITS2). To estimate the level of infection, the number of black spots was counted to calculate prevalence, mean abundance, and mean intensity. Phylogenetic inference based on maximum likelihood and Bayesian inference revealed a rare black spot disease taxon, genus Uvulifer, which represents one of the first records in Europe on fish (second intermediate host), a first record from a Phoxinus host, a first record for the Adriatic drainage and Croatia, and a first record for Southern Europe in general. Furthermore, the monogenean was identified as Gyrodactylus sp., potentially representing a new species.