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This study describes the parasite community of non-native brown bullhead, Ameiurus nebulosus (Actinopterygii: Ictaluridae), collected at three sites in the river Vistula Basin (Lake Svitiaz, Lake Pisochne, and Lake on Plastova) and one site in the river Diester Basin (Lake Stryiska), in Ukraine. Our data represent the first comprehensive study of parasite community in this fish species in Europe. Sixteen parasite taxa were found, including species co-introduced from North America and species acquired in the European range. Maximum parasite richness (13 spp.) was recorded in Lake Svitiaz situated in a Natural Protected Area, while lowest species richness (3 spp.) was observed at Lake on Plastova, an artificial pond in the city of Lviv. Three co-introduced monogenean species, Gyrodactylus nebulosus, Ligictaluridus pricei and Ligictaluridus monticellii, are recorded in Ukraine for the first time, widening the knowledge of the European distribution of these North American parasites. Metric features for hard parts of invasive and native monogeneans showed overlap in ligictalurid parasites, but slightly smaller metrics in Ukrainian G. nebulosus, possibly reflecting water temperature during fish sampling. Though prevalence and abundance of acquired parasites was relatively low, infection parameters for metacercariae of Diplostomum spp. were relatively high at Lake Svitiaz and the natural Lake Stryiska in Lviv. In two lakes in the Vistula basin, we found high prevalence and abundance of Anguillicola crassus, an Asian nematode infecting eels, possibly supporting the invasional meltdown hypothesis. Our study confirms both further spread of non-native parasites in Europe and use of non-native fish as competent hosts for local native and introduced parasites.

This study provided a preliminary comparative analysis of meiobenthic assemblages in different habitats of the Snake Island Marine Protected Area (MPA). Meiobenthos was studied in three habitats: Exposed Black Sea upper infralittoral rock with Corallinales turf (MB142), Mytilid dominated exposed Black Sea upper infralittoral rock with foliose algae (no Fucales) (MB143) and Black Sea infralittoral sand and muddy sand without macroalgae (MB542). A total of 10 higher meiobenthos taxa were recorded in the different habitats: 5 permanent groups (Platyhelminthes, Nematoda, Harpacticoida (Copepoda), Ostracoda, Halacaridae) and 5 temporary groups (Oligochaeta, Polychaeta, Bivalvia, Gastropoda, Cyrripedia). The preliminary study of meiobenthos in the habitats of the Snake Island MPA showed that habitat MB143 was more favourable for meiobenthos, with the highest mean density and biomass (190 655 ± 23 004 ind.-m-2 and 3170.90 ± 412.15 mg-m-2, respectively). The comparative nMDS and cluster analyses based on the density of meiobenthos taxa in the Snake Island MPA showed that the meiofauna of both MB142 and MB143 differed significantly from the MB542 habitat, with Bivalvia and Ostracoda making the largest percentage contribution to these differences. The meiobenthos assemblages in the different habitats of the Snake Island MPA were similar to the other regions of the Black Sea with some unique features (e. g. relatively lower total meiobenthos density, high percentage of ostracodes on the algal substrate, etc.). Further studies on the characteristics of meiobenthos taxa assemblages in other Black Sea MPAs could lead to the estimation of meiobenthos assemblage patterns and their possible use in biomonitoring. [ABSTRACT FROM AUTHOR]

Examination of western tubenose goby (Proterorhinus semilunaris) from the River Dyje (Czech Republic, Danube basin) for metazoan parasites revealed the presence of metacercariae of Cyathocotyle prussica Mühling, 1896 (Digenea: Cyathocotylidae) in both muscle tissue and the peritoneal cavity. This is the first time that tubenose gobies have been reported as an intermediate host for C. prussica, and the first time that C. prussica metacercariae have been registered parasitising fish hosts in the Czech Republic. Here, we describe the morphology of metacercariae and five-day preadults, cultivated in vitro, and discuss the importance of recently established, non-native species as suitable hosts for this parasite.

Paracanthocephaloides kostylewi (Meyer, 1932), a rare parasite of the common sole Solea solea, previously placed in the Arhythmacanthidae, is transfered to the genus Solearhynchus de Buron & Maillard, 1985 of the family Echinorhynchidae as Solearhynchus kostylewi (Meyer, 1932) new comb., because its proboscis is armed by a single type of hooks, the posterior hook in each row is pinlike and with feebly developed root. The species is redescribed on the basis of newly collected material from the Gemlik Bay, Sea of Marmara. A key to the species of Solearhynchus is provided.

A parasitological study of Ponto-Caspian gobies, including the monkey goby Neogobius fluviatilis, racer goby Babka gymnotrachelus and tubenose goby Proterorhinus semilunaris, carried out over four years in the lower Vistula River is described. These fish species represent one of the most impressive invasions of European inland waters, connected with the spontaneous, east-to-west intracontinental movement observed in the last two decades. The parasite community consisted of 24 taxa. Typical for racer goby were: Trichodina domerguei, Diplostomum pseudospathaceum, Gyrodactylus proterorhini and glochidia of unionids. The list of parasites typical for monkey goby is supplemented with: Tylodelphys clavata (met.) and Eimeria sp., while the glochidia were rarely detected in this fish host. Holostephanus spp., Apatemon gracilis, Diplostomum gobiorum and glochidia predominated in parasite fauna of tubenose goby. Unlike the other species tested, P. semilunaris was poorly infected with T. domerguei and G. proterorhini. Parasites commonly distributed through native fishes in the observed area prevailed in gobies. Species rare in natives were also numerously represented. In this way, alien fish reinforce populations of those parasites in invaded waters. Parasites dragged to the colonized area (G. proterorhini, Holostephanus spp., A. gracilis and D. gobiorum) complement the community. Larval stages were typical for parasite fauna of all studied gobies.

The parasites of the Asian invasive fish, Chinese sleeper Perccottus glenii, were studied in 6 localities in different parts of Ukraine. In total, 15 taxa of parasites were registered; among them were 1 species of Microsporidia, 5 species of ciliates, 2 species of cestodes, 2 species of trematodes, 2 species of nematodes, 1 species of acanthocephalan, 1 species of parasitic crustacean and 1 mollusk (glochidia). The invasive Chinese sleeper is included as a paratenic host in the life cycle of the parasites of indigenous reptiles in Europe. The non-indigenous cestode Nippotaenia mogurndae occurred in the intestine of the Chinese sleeper from the Ivachiv Reservoir (Dniester River basin). This cestode is recorded for Ukrainian fauna for the first time. In addition, 3 species of parasites were recorded in the Chinese sleeper for the first time: Nicolla skrjabini, Cosmocephalus obvelatus and Pomphorhynchus laevis. We note the low similarity among the different localities and the low parasite richness, that suggest that the parasite fauna of the Chinese sleeper in Ukraine is in transition.

Two Ponto-Caspian gobiid species, the racer goby, Babka gymnotrachelus, and the monkey goby, Neogobius fluviatilis, the introduced fishes in the Vistula River, Poland, were found being infected with metacercariae of Bucephalus polymorphus. The encysted larvae were located in muscles and fins of these fish. The adult specimens occurred in the gut of another non-indigenous species, the Chinese sleeper Perccottus glenii. The life cycle of B. polymorphus in the Vistula River drainage includes three non-indigenous components: 1) the zebra mussel Dreissena polymorpha, the source of cercariae; 2) gobiids (the racer and monkey gobies), which are new in this water drainage but could play more important role in the life cycle than habitual cyprinids, thanks to their small size (favorable in transmission through the food-web); 3) the Chinese sleeper, a new accidental definitive host. The presence of these non-indigenous components in the life cycle maintains the distribution and further spread of B. polymorphus in the colonized area.

Monogenean parasites are often co-introduced with their fish hosts into novel areas. This study confirmed co-introduction of two dactylogyrids, Dactylogyrus squameus Gusev, 1955 and Bivaginogyrus obscurus (Gusev, 1955), and a newly described gyrodactylid species, Gyrodactylus pseudorasborae n. sp. into Europe along with their fish host, the invasive topmouth gudgeon Pseudorasbora parva (Temminck & Schlegel) from East Asia. All three species were observed in the lower Dnieper and middle Danube basin regions and had slightly larger haptoral hard parts than the same parasites in their native range. While dactylogyrids occurred sporadically, we recorded regular infection by G. pseudorasborae n. sp. at relatively high prevalence and abundance. This latter species was observed in both the native and non-native range of topmouth gudgeon, and resembles Gyrodactylus parvae You et al., 2008 recently described from P. parva in China. Both species were distinguished based on genetic analysis of their ITS rDNA sequence (6.6% difference), and morphometric differences in the marginal hooks and male copulatory organ. Phylogenetic analysis of dactylogyrid monogeneans showed that B. obscurus clustered with Dactylogyrus species parasitising Gobionidae and Xenocyprididae, including D. squameus, supporting recent suggestions of a paraphyletic origin of the Dactylogyrus genus. In addition to co-introduced parasites, topmouth gudgeon was infected with a local generalist, G. prostae Ergens, 1964, increasing the number of monogeneans acquired in Europe to three species. Nevertheless, monogenean infections were generally lower in non-native host populations, potentially giving an advantage to invading topmouth gudgeon., (© M. Ondračková et al., published by EDP Sciences, 2023.)

A species of acanthocephalan new to science from soleid fishes in the Mediterranean Sea and the Sea of Marmara is described. The new species is characterised by individuals having a club-shaped proboscis armed with 12-13 rows of 6-7 rooted hooks of a single type, a basal cerebral ganglion, and tegumental spines on the anterior two thirds of the body. Males have six cement glands and females show spines around the genital opening. To accommodate this species, a new genus, Harpagorhynchus n. gen., and a new subfamily in Echinorhynchidae, Harpagorhynchinae n. sub-fam., are erected. A critical review of the literature on echinorhynchid species infecting soleid fishes in the Mediterranean basin showed that Solearhynchus soleae (Porta, 1906) should be considered a junior synonym of S. rhytidotes (Monticelli, 1905) and that S. kostylewi (Meyer, 1932) is a valid species. An identification key of acanthocephalans of Mediterranean soleids is provided., (© Y. Kvach & I. de Buron, published by EDP Sciences, 2019.)