Parasite and genetic diversity of big-scale sand smelt (Atherina boyeri Risso, 1810) populations in their natural and expansion ranges in Ukraine.

The big-scale sand smelt (Atherina boyeri) is an Atlanto-Mediterranean amphidromous fish species found within the Black Sea. Here, we assess differences in the parasite fauna of big-scale sand smelt populations from their natural range in the northwestern Black Sea and from their expansion range in the Lower and Middle River Dnipro. In addition, we undertook a microsatellite analysis to assess the genetic similarity of fish from the different locations. We found that the parasite community of fish in their natural range was wider than that from their expansion range. While the Gulf of Odesa was most distant from all other localities by parasite community composition and the Dnipro Reservoir was characterised by an absence of parasites (newest and most distant expansion locality), only fish from the Danube Delta showed a significant genetic difference. Our results suggest that the parasite community of big-scale sand smelt is primarily influenced by environmental factors, such as habitat type, water salinity and/or prey composition. Both microsatellite analysis and parasite community species composition (e.g. the presence of the marine Telosentis exiguus in the Kakhovka Reservoir and freshwater Raphidascaris sp. in the Gulf of Odesa) confirmed that populations in the River Dnipro reservoirs had, at some time, been connected with native marine populations, thus also confirming the species' amphidromous nature.

Population genetic structure, parasite infection and somatic condition of pumpkinseed Lepomis gibbosus (Actinopterygii: Centrarchidae) in the Oder river basin.

In Poland, distribution of non-native pumpkinseed Lepomis gibbosus (Centrarchidae) is strictly limited to the Oder river basin, where it was introduced in the early 20th century. Recently, several populations have been found in waterbodies adjacent to the Oder, particularly in its lower reaches. In this study, we compare the genetic relatedness of populations in the Oder basin with other European populations using nuclear (microsatellite) and mitochondrial (partial cytochrome c oxidase subunit I; cox1) markers. Microsatellite analysis indicated that four populations in the lower Oder form a separate cluster, while one in the middle Oder clustered with Danubian populations, from where probably having been introduced. Microsatellite data suggested that the lower Oder populations differ from other non-native European populations, making it impossible to estimate the source of introduction. Nevertheless, analysis of cox1 indicated that Oder pumpkinseeds belong to the same haplotype as the vast majority of European populations. Parasitological examination confirmed the presence of two North American species, the monogenean Onchocleidus dispar and trematode Posthodiplostomum centrarchi, in the lower Oder, both previously unknown in the region. Fifteen other parasite species were acquired, including glochidia of invasive Sinanodonta woodiana. In the middle Oder, parasite infection was more limited. Fish from the Gryfino Canal, considered one of the most invasive populations in Europe, showed the highest parasite abundance and diversity, and the highest somatic condition and growth rate due to warm water released from the Dolna Odra power plant. Our results highlight significant differences in somatic condition and parasite infection in long-established non-native pumpkinseed populations in the same river system, reflecting mainly environmental conditions.

The role of the non-indigenous pumpkinseed Lepomis gibbosus (Actinopterygii: Centrarchidae) in the life cycle of Bothriocephalus claviceps (Cestoda: Bothriocephalidae) in Europe.

Infection of non-indigenous pumpkinseed (Lepomis gibbosus, Centrarchidae) with the bothriocephalidean cestode Bothriocephalus claviceps (Cestoda: Bothriocephalidae) was confirmed at several sites in the lower Oder river basin in Poland. The preferred host for this cestode species is the European eel (Anguilla anguilla), with a wide range of other fish species serving as paratenic hosts. The pumpkinseed showed a relatively high prevalence and abundance of larvae, along with several mature and gravid specimens, thereby confirming development of B. claviceps to the adult stage in an alternative host. As such, the pumpkinseed may represent an additional definitive host for this cestode, in addition to its role as a paratenic host, as previously recorded in other European regions. Our results indicate that inclusion of pumpkinseed as an additional definitive host in the cestode's life cycle, high infection of pumpkinseed with B. claviceps larvae and inclusion of pumpkinseed in the eel's diet could potentially lead to increased parasite pressure on native fish hosts. Further comparative studies or experimental testing will be required to confirm this.

Low-level pathogen transmission from wild to farmed salmonids in a flow-through fish farm.

While the potential effects of pathogens spread from farmed fish to wild populations have frequently been studied, evidence for the transmission of parasites from wild to farmed fish is scarce. In the present study, we evaluated natural bacterial and parasitic infections in brown trout (Salmo trutta m. fario) collected from the Cerná Opava river (Czech Republic) as a potential source of infections for rainbow trout (Oncorhynchus mykiss) reared in a flow-through farm system fed by the same river. The prevalence of bacterial and protozoan infections in farmed fish was comparable, or higher, than for riverine fish. Despite this, none of the infected farmed fish showed any signs of severe diseases. Substantial differences in metazoan parasite infections were observed between wild and farmed fish regarding monogeneans, adult trematodes, nematodes, the myxozoan Tetracapsuloides bryosalmonae found in riverine fish only, and larval eye-fluke trematodes sporadically found in farmed fish. The different distribution of metazoan parasites between brown and rainbow trout most probably reflects the availability of infected intermediate hosts in the two habitats. Despite the river being the main water source for the farm, there was no significant threat of parasite infection to the farmed fish from naturally infected riverine fish.

Gyrodactylus ginestrae n. sp. (Monogenea: Gyrodactylidae), a parasite of the big-scale sand smelt, Atherina boyeri Risso, 1810 (Actinopterygii: Atherinidae) from the Black Sea.

We describe a new species, Gyrodactylus ginestrae n. sp., a parasite of the big-scale sand smelt (Atherina boyeri) from the Black Sea. This is the third monogenean species known from this fish host, found at 70% prevalence, but at relatively low abundance (1.9), on fish gills and fins. The new species is, both morphologically and genetically, most similar to G. salinae, which parasitizes the killifish Aphanius fasciatus (Cyprinodontidae) in the Mediterranean region. These species differ in the size of the haptoral hard parts and the number of small spines of the male copulatory organ. For molecular characterization, the internal transcribed spacer 1 (ITS1), 5.8S rRNA gene, and the internal transcribed spacer 2 (ITS2) were sequenced, completed by a fragment of the COII gene, thereby representing the first molecularly characterized gyrodactylid species from the Black Sea. Phylogenetic reconstruction based on the ITS1-5.8S-ITS2 sequence data indicated the position of G. ginestrae n. sp. in the marine "rugiensis" group of G. (Paranephrotus) and G. (Neonephrotus) subgenera which is part of the monophyletic "long ITS1" group. Taking into account the similarity of G. ginestrae n. sp. to several monogeneans from the Atlantic and Mediterranean regions, we suggest the Boreal-Atlantic origin of this species.

Methodological issues affecting the study of fish parasites. III. Effect of fish preservation method.

The aim of this study was to evaluate the influence of preservation method on the results of parasite community studies. Two host species, European perch Perca fluviatilis and European bitterling Rhodeus amarus, were examined for parasites after having been subjected to 4 different storage treatments: freezing, preservation in 4% formaldehyde or 70% ethanol and transportation of live (fresh) fish as a control. Preservation prior to dissection resulted in a loss of information, leading to incomplete quantitative data (all preservation treatments), qualitative data (ethanol and formaldehyde preservation) and a lowered ability to determine parasites to species level based on morphology compared to dissecting fresh fish. Of the more abundant taxa, only crustaceans and acanthocephalans provided relatively even results between treatments. We conclude that preservation media, such as ethanol or formaldehyde, significantly affects the ability to obtain precise parasite community data; hence, we recommend the use of freshly sacrificed fish for parasite community studies whenever possible. Alternatively, freezing may prove acceptable for evaluating parasite community taxonomic composition.

A revision of the genus Aphalloides (Digenea: Cryptogonimidae), parasites of European brackish water fishes.

Trematodes of the genus Aphalloides Dollfus, Chabaud & Golvan, 1957 reach maturity in their second intermediate host, small fishes of the family Gobionellidae, genera Pomatoschistus and Knipowitschia. Two morphologically similar species have been described from European waters: Aphalloides coelomicola Dollfus et al., 1957 in the Mediterranean Sea (including the brackish Black Sea region) and Aphalloides timmi Reimer, 1970 in the Baltic Sea. There was no difference in morphology and morphometry for specimens corresponding to A. coelomicola and A. timmi and examination of the 28S rDNA sequence confirmed the similarity. Based on these results, these two species are synonymized and A. coelomicola redescribed.

Study of Loma acerinae (Microsporidia) detected from three Ponto-Caspian gobies (Gobiidae) in Ukraine.

A previously recognized Glugea-belonging Microsporidia (G. melanostomi, G. markievichi, G. naidenovi) were found in the intestinal mucosa of Neogobius melanostomus, N. fluviatilis, and Proterorhinchus semilunaris (Teleostei, Gobiidae) from lower Dnieper River and Black Sea coastal inlets, Ukraine. Light microscope observations demonstrated small spherical xenomes about 0.35 mm in diameter filled by developmental stages of parasites. Mature spores were ellipsoidal, slightly narrowed at anterior pole, sometimes ovoid or elongate in shape approximately 3.1-4.5 × 2.0-2.9 µm in size. The stained spores were elongate ovoid that are measured about 2.3-4.3 × 1.6-3.4 µm. Ultrastructural study showed that xenoma wall consisted of finely granular layer up to 350 nm wide. Numerous host-derived collagenous fibers adhered to the xenoma wall were noticed. Microtubular inclusions about 40 nm in diameter occupied the episporontal space. Mature spores displayed the polar filament arranged in one row. One to two last turns of polar filament were sharply tapered to half of diameter. The number of polar filament turns varied depending of host infected from 10 (9 + 1) in N. melanostomus to 13 (11 + 2) in N. fluviatilis and 14 (13 + 1) in P. semilunaris. The endospore thickness varied depending of host infected from 30-35 nm in case of N. fluviatiis to 40-50 nm in P. semilunaris and 60-80 nm in N. melanostomus. SSU 16S rRNA sequence analysis, blast searches, and ultrastuctural data revealed similarity of all studied microsporidians with Loma acerinae (Jirovec, 1930).

Methodological issues affecting the study of fish parasites. II. Sampling method affects ectoparasite studies.

In this study, we assessed the impact of sampling method on the results of fish ectoparasite studies. Common roach Rutilus rutilus were sampled from the same gravel pit in the River Dyje flood plain (Czech Republic) using 3 different sampling methods, i.e. electrofishing, beach seining and gill-netting, and were examined for ectoparasites. Not only did fish caught by electrofishing have more of the most abundant parasites (Trichodina spp., Gyrodactylus spp.) than those caught by beach seining or gill-netting, they also had relatively rich parasite infracommunities, resulting in a significantly different assemblage composition, presumably as parasites were lost through handling and 'manipulation' in the net. Based on this, we recommend electrofishing as the most suitable method to sample fish for parasite community studies, as data from fish caught with gill-nets and beach seines will provide a biased picture of the ectoparasite community, underestimating ectoparasite abundance and infracommunity species richness.

Methodological issues affecting the study of fish parasites. I. Duration of live fish storage prior to dissection.

We tested the ability of parasite species to respond quickly to artificial conditions (e.g. by changing abundance or even decreasing to extinction) while host fish species were being held alive prior to dissection. Prussian carp Carassius gibelio were sampled by electrofishing from 2 ponds alongside the River Dyje (Czech Republic) during 'cold' and 'warm' seasons. All fish were transported to the laboratory in aerated pond water and kept in a 1 m3 outdoor basin with aged tap water for 6 d. Twenty fish were dissected on consecutive days (total 120 fish for each site). Our results indicated that there was little change in parasite loading over the first 3 d of holding, suggesting no impact on parasitological studies undertaken over this period. From the fourth day, however, overall parasite abundance increased due to rapid reproduction of some parasite species, especially gyrodactylids in the cold season and dactylogyrids in the warm season. Parasite diversity appeared less stable in the warm season, with significant differences being registered as early as the second day. In addition to holding period, environmental conditions during fish holding will also play an important role in parasite community shifts.

Acanthocephalans of the genus Megistacantha Golvan, 1960 (Palaeacanthocephala: Rhadinorhynchidae) in two African mormyrid fishes (Actinopterygii: Mormyridae).

The genus Megistacantha Golvan, 1960 was originally described as monotypic with Megistacantha horridum (Lühe, 1912) from a mormyrid fish in Africa as its type- and only species. This species was described from one female specimen, but no description of the male was provided. In this study, the male of M. horridum is described for the first time. In addition, a new species, Megistacantha sanghaensis n. sp., is described from the Cornish jack Mormyrops anguilloides L., a mormyrid fish from the River Sangha, Dzanga-Sangha Protected Areas, Central African Republic. The diagnosis of Megistacantha Golvan, 1960 is amended and a key to its two species is provided.

Parasitization of invasive gobiids in the eastern part of the Central trans-European corridor of invasion of Ponto-Caspian hydrobionts.

Four gobiid species, Babka gymnotrachelus, Neogobius melanostomus, Neogobius fluviatilis, and Proterorhinus semilunaris, were parasitologically studied in different localities of the Dnieper and Vistula river basins. The highest number of parasitic species was found in N. fluviatilis (35 taxa). The parasite fauna of N. melanostomus, B. gymnotrachelus, and P. semilunaris consists of 23, 22, and 15 taxa, respectively. The species accumulation curves show stable accumulation of parasite species by all four fish hosts along the studied part of the corridor, from the Dnieper Estuary to the Vistula River delta. The plot reveals also that the studied gobies lose the parasites common in the host native range and accept new parasites from the colonized area. In the case of N. melanostomus, it complies with the enemy release hypothesis, as the parasite load was low in the invaded area if compared to the native range. The three other alien gobies are vector for Gyrodactylus proterorhini in the Baltic basin. Moreover, populations of this alien monogenean tend to be more abundant in their new range in comparison with the Black Sea basin. In general, the number of parasite species in the colonized area was of the same rank as in the native one for N. fluviatilis, and even higher for B. gymnotrachelus. This results from accumulating new parasite species along the gobiid invasion route. In particular, the N. fluviatilis, B. gymnotrachelus, and P. semilunaris lost some of their native parasites and gained the local ones after entering the post-dam part of the Vistula River; it can be interpreted as a partial escape from parasites.

Comparative Analysis of Parasite Load on Recently Established Invasive Pumpkinseed Lepomis gibbosus (Actinopterygii: Centrarchidae) in Europe.

PURPOSE: The aim of this study was the comparative analysis of the parasite communities of new populations of invasive pumpkinseed (Lepomis gibbosus) in western Ukraine with pumpkinseed from Czechia, where populations have rapidly expanded over the last two decades. METHODS: Sampling took place at three localities in the western part of Ukraine (i.e. Dobrotvir Reservoir (Vistula basin), Burshtyn Reservoir (Dniester basin), Mynai Pond (Danube basin)) and four in Czechia (i.e. Oxbow D2, Herspický Pond (Danube basin), and Kolín oxbow and Rímov Reservoir (Elbe basin). RESULTS: In total, 11 parasite taxa were recorded in Ukraine and 17 in Czechia. Four species were co-introduced from North America with their host, i.e. the myxosporean Myxobolus dechtiari, the monogeneans Onchocleidus dispar and Onchocleidus similis, and metacercariae of a trematode Posthodiplostomum centrarchi. High dominance indices were related to a high abundance of co-introduced parasites, i.e. O. similis in Mynai pond and P. centrarchi in Dobrotvir Reservoir. Overall abundance of acquired parasites was generally low. CONCLUSION: This study shows that parasite communities in recently established pumpkinseed populations in the western part of Ukraine and Czechia are less diverse than those established in Europe for decades. The generally low parasite load in these new populations may play an important role in their ability to successfully establish and create strong populations by providing a competitive advantage over local species.

The parasites of a successful invader: monogeneans of the Asian topmouth gudgeon Pseudorasbora parva, with description of a new species of Gyrodactylus.

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.

Title: Les parasites d'un envahisseur à succès : les monogènes du goujon asiatique Pseudorasbora parva, avec description d'une nouvelle espèce de Gyrodactylus. Abstract: Les parasites monogènes sont souvent co-introduits avec leurs hôtes poissons dans de nouvelles zones. Cette étude a confirmé la co-introduction de deux Dactylogyridae, Dactylogyrus squameus Gusev, 1955 et Bivaginogyrus obscurus (Gusev, 1955), et d'une espèce de Gyrodactylidae nouvellement décrite, Gyrodactylus pseudorasborae n. sp. en Europe, en même temps que leur hôte poisson, le goujon envahissant Pseudorasbora parva (Temminck & Schlegel) qui vient d'Asie de l'Est. Les trois espèces ont été observées dans les régions du bas Dniepr et du bassin moyen du Danube et avaient des parties sclérifiées haptorales légèrement plus grandes que les mêmes parasites dans leur aire de répartition d'origine. Alors que les Dactylogyridae étaient rares, nous avons enregistré une infection régulière par G. pseudorasborae n. sp. à une prévalence et une abondance relativement élevées. Cette dernière espèce a été observée à la fois dans l'aire de répartition indigène et non indigène du goujon asiatique et ressemble à Gyrodactylus parvae You et al., 2008 récemment décrit chez P. parva en Chine. Les deux espèces ont été distinguées sur la base de l'analyse génétique de leur séquence ITS de l'ADNr (différence de 6,6 %) et des différences morphométriques dans les crochets marginaux et l'organe copulateur mâle. L'analyse phylogénétique des monogènes Dactylogyridae a montré que B. obscurus se regroupait avec des espèces de Dactylogyrus parasitant les Gobionidae et les Xenocyprididae, y compris D. squameus, soutenant les suggestions récentes d'une origine paraphylétique du genre Dactylogyrus. En plus des parasites co-introduits, le goujon asiatique était infecté par un généraliste local, G. prostae Ergens, 1964, portant le nombre de monogènes acquis en Europe à trois espèces. Néanmoins, les infections par les monogènes étaient généralement plus faibles dans les populations d'hôtes non indigènes, donnant potentiellement un avantage à l'invasion du goujon asiatique.

The colonization of the invasive round goby Neogobius melanostomus by parasites in new localities in the southwestern Baltic Sea.

The round goby Neogobius melanostomus is a bottom-dwelling fish native for the Ponto-Caspian basin, which started to colonize the Baltic Sea since 1991. The parasites of this fish species in the southwestern Baltic region are studied for the first time. The round goby in the SW Baltic Sea was infected with 12 parasite species: 1 species of Microsporidia, 1 species of Monogenea, 1 of Cestoda, 3 species of Trematoda, 3 species of Nematoda, 2 of Acanthocephala, and 1 species of Bivalvia. Microsporidia genus species have the great tendency to join the infracommunity in all localities, except the Stettiner Haff, where this tendency have Diplostomum spathaceum met and Unio sp. glochidia. The round goby was colonized by seven new parasites species not found in this fish in the Baltic Sea earlier: Microsporidia gen. sp., Gyrodactylus rugiensis, Bucephalus polymorphus, Cosmocephalus obvelatus L3, Eustrongylides excisus L3, Paracuaria adunca L3, Unio sp. glochidia. Microsporidia gen. sp., G. rugiensis, and Unio sp. are new parasites for the round goby. In general, the processes of colonization have the same tendency as in the Gulf of Gdansk.

Acanthocephaloides irregularis n. sp. (Acanthocephala: Arhythmacanthidae) from marine fishes off the Ukrainian Black Sea coast.

Acanthocephaloides irregularis n. sp. (Arhythmacanthidae) is described from four species of marine fishes in the Gulf of Odessa and Sukhyi Lyman, Ukrainan Black Sea waters, making it the tenth species of the genus. The hosts are the combtooth blenny Parablennius zvonimiri (Kolombatovic) (Blenniidae), the mushroom goby Ponticola eurycephalus (Kessler) (Gobiidae), the tubenose goby Proterorhinus marmoratus (Pallas) (Gobiidae) and the black-striped pipefish Syngnathus abaster Risso (Syngnathidae). The new species is most similar to its closest relative, Acanthocephaloides propinquus (Dujardin, 1845), in proboscis shape and armature (12 longitudinal rows of 5 hooks) and the shape of the trunk, reproductive system and lemnisci, but differs in having randomly distributed trunk spines. These trunk spines are organised in circular rings of individual spines separated by aspinose zones. The new species is also unique in having an anterior trunk collar, a very large triangular cephalic ganglion, nucleated pouches at the posterior end of the proboscis receptacle, and hooks and spines with roots bearing anterior manubria. Valid and invalid species of Acanthocephaloides Meyer, 1932 are listed and a key to all ten species is included.

Telosentis exiguus (von Linstow, 1901) (Palaeacanthocephala: Illiosentidae), a generalist parasite of fishes in the Mediterranean basin.

The morphology of material of the acanthocephalan genus Telosentis van Cleave, 1923 from different parts of the Mediterranean basin is examined in order to assess the validity of T. molini van Cleave, 1923. A redescription of T. exiguus, a generalist species of fishes in the Mediterranean basin, is presented especially in relation to the number of proboscis hooks. The main characteristic of T. exiguus is a cylindrical or club-shaped proboscis, which is covered with 12 longitudinal rows of 14-19 hooks in males and 16-20 in females. Males and females differ in both body size and the number of proboscis hooks. T. molini is considered a junior synonym of T. exiguus. A key to the species of Telosentis is presented.

Description of Harpagorhynchus golvaneuzeti n. gen. n. sp. (Acanthocephala, Harpagorhynchinae n. sub-fam.) with a review of acanthocephalan parasites of soleid fishes in the Mediterranean Basin.

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.

European distribution for metacercariae of the North American digenean Posthodiplostomum cf. minimum centrarchi (Strigeiformes: Diplostomidae).

Metacercariae of a North American digenean Posthodiplostomum cf. minimum centrarchi (Strigeiformes: Diplostomidae), have been reported from seven localities in Europe, with cysts recorded in the mesentery and internal organs of two invasive non-indigenous fishes (Lepomis gibbosus and Micropterus salmoides) from sites in Bulgaria, the Czech Republic and Portugal. Analysis of rDNA locus ITS1-ITS2-28S confirmed a closer relationship to the American Posthodiplostomum species than the common European species P. cuticola or P. brevicaudatum. Our data indicate limited potential of this parasite for switch to local fish fauna and confirm the occurrence at distant sites across Europe, suggesting that birds as definitive parasite hosts may play an important role for parasite dispersal. Further detailed studies are needed to confirm the actual means of introduction to Europe.

Metazoa parasites of the invasive round goby Apollonia melanostoma (Neogobius melanostomus) (Pallas) (Gobiidae: Osteichthyes) in the Gulf of Gdansk, Baltic Sea, Poland: a comparison with the Black Sea.

The known metazoa parasite fauna of the invasive round goby Apollonia melanostoma (formerly Neogobius melanostomus) consists of 12 species. The core of the parasite fauna comprises two species: Cryptocotyle concavum and Diplostomum spathaceum; secondary species are absent; satellite species include Cercariae gen. sp. and Ergasilus sieboldi; rare species are Acanthocephalus lucii, Anguillicola crassus, Bothriocephalus sp., Dichelyne minutus, Hysterothylacium aduncum, Pomphorhynchus laevis, Piscicola geometra, and Tylodelphys clavata. Fifty percent of metazoa parasites that occurred in the invasive round goby in the Gulf of Gdansk (an invasion that was first detected in 1990) are also typically found in the native Gulf of Gdansk gobiids. The round goby hosts common fish parasite species: C. concavum and D. minutus, but none that are unique to the species and no Ponto-Caspian parasites. Notably, the parasite species of the invasive round goby in the Gulf of Gdansk includes species that are atypical for this species in its native habitat. In its new habitat, the round goby variously serves the roles of definitive, second intermediate, and paratenic host for different parasite species. The fish species is involved in a parasitic system that includes fish-eating birds, fishes of different ecological groups (predatory, planktivorous, and benthivorous), and invertebrates.