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Owing to their widespread use, pharmaceuticals have become important pollutants of the aquatic environment. Pharmaceuticals and parasites can affect the immunity, physiology and behaviour of target organisms, both singly and through interaction. In this study, we related pharmaceutical concentration, parasite infection and condition in brown trout (Salmo trutta m. fario) collected at localities upstream and downstream of a sewage treatment plant (STP). The sites were separated by a weir preventing fish migration. Pharmaceutical number and concentrations differed significantly between sites. Antibiotics and antidepressants were found at the highest concentrations at both localities. Though fish condition and overall parasite abundance did not differ between sites, there was a significant difference in parasite community composition. A higher abundance of monogenean ectoparasites, along with a lower abundance of endoparasites, was observed at the downstream locality. The adverse effect of pharmaceutical load on ecto- and endoparasitic species on brown trout was further confirmed at the individual level using multivariate analysis. Both the number and concentration of pharmaceuticals in fish tissues reflected their high incidence in the environment, confirming the ability of trout to bioaccumulate pharmaceuticals. This could have important consequences on fish health, particularly in small streams where STP effluent represents a high proportion of stream flow.

International audience; Species introductions often coincide with loss of genetic diversity and natural enemies. Anthropogenic translocation of the North-American pumpkinseed Lepomis gibbosus (L., 1758) (Centrarchidae) and its further spread have resulted in recent species establishment in most European countries. This study determines genetic differentiation of non-native European pumpkinseed populations and identifies how their genetic structure relates to the distribution and abundance of parasite species. Microsatellite analysis indicated presence of three genetic lineages, which were well supported by discriminant analysis based on parasite abundance data. The first lineage clustered pumpkinseed populations from northern and southern France and showed high allelic richness, heterozygosity and parasite richness. The second included populations along the ‘‘Southern invasion corridor’’ connecting the rivers Rhine, Main and Danube. The fish exhibited low to high genetic and parasite diversity and generally high parasite abundance. The third lineage clustered populations with low genetic and parasite diversity, located in Portuguese reservoirs and water bodies along the upper Elbe. Parasite species richness was significantly associated with host microsatellite heterozygosity and allelic richness, a trend partially affected by richness of North-American parasites. Furthermore, our results indicate that parasite community composition may serve as a useful biological tool to discriminate non-native fish populations and their inter-relationships.

Gyrodactylid parasites were observed on non-native populations of North-American freshwater catfishes, Ameiurus nebulosus and Ameiurus melas (Siluriformes: Ictaluridae), at several sites in the Elbe River basin, Czech Republic, Europe. Using a combination of morphological and genetic analyses, the parasites infecting A. nebulosus were determined to be Gyrodactylus nebulosus, a North American parasite co-introduced to Europe along with its Ameiurus fish hosts. Subtle morphometrical differences, as well as seasonal variations, were observed among parasites collected from A. nebulosus and A. melas. The host-related variation was further supported through genetic analysis of the partial 18S rDNA, ITS1-5.8S-ITS2 and COI, showing 0.2, 3.0 and 4.8% divergence, respectively. Consistent genetic differences indicated there were two distinct genotypes. Subtle morphological differences associated with the shape of sickle toe, anchor root and ventral bar membrane, according to host species, also supported the description of a new cryptic species, Gyrodactylus melas n. sp., infecting A. melas. Multivariate morphometrical analysis of haptoral hard parts showed significant differences between the anchor lengths of G. nebulosus and G. melas n. sp. However, the measurements of the haptoral hard structures partially overlapped between species, limiting the usage of these parameters for species delineation.

Understanding non-native species dispersal is vital for their future management. The round goby (Neogobius melanostomus) has greatly extended its range since the 1990s, with commercial shipping being the main vector. However, our knowledge regarding their secondary dispersal from points of introduction is surprisingly limited. In this study, a series of field experiments were undertaken on a mid-sized river to assess goby dispersal patterns within an established population, following a simulated release of a large number of propagules, or at a simulated invasion front. Most of the established population remained stationary and just a few individuals undertook long-distance dispersal (principally upstream). Mean distance travelled was 1.1 m·day−1 (max. 29.6 m·day−1). While site fidelity appeared to last for most of the year (including winter), it was surprisingly relaxed during the spawning season. Concentrated release of a large number of propagules resulted in appreciably greater movement rates than in the established population, with upstream movement again dominating. In general, smaller, mostly male fish tended to move further and appeared as first colonizers in uninvaded areas.

Non-native species are known to escape their parasites following introduction into a new range, but they also often acquire local parasites as a function of time since establishment. We compared the parasite faunas of five non-native Ponto-Caspian gobies (Gobiidae) and local fish species (Perca fluviatilis, Gymnocephalus cernua, Gobio gobio) in three European river systems; the Rivers Rhine, Vistula and Morava, where Ponto-Caspian gobies were introduced 4-13 years prior to the study. Overall parasite species richness was considerably lower in non-native gobies compared to local fish species, and the same result was found at the component and infra-community levels. Both parasite abundance and diversity greatly varied among the regions, with the highest values found in the River Vistula (Wloclawski Reservoir), compared to a relatively impoverished parasite fauna in the River Morava (Danube basin). While only half of parasite species found in local hosts were acquired by non-native gobies, most of the parasites found in gobies were shared with local fish species related either phylogenetically (percids) or ecologically (benthic gudgeon), including the co-introduced monogenean Gyrodactylus proterorhini. As a result, similarity in parasite communities strongly reflected regional affiliation, while phylogenetic distances between fish host species did not play a significant role in parasite community composition. In accordance with other studies, all parasites acquired by gobies in their new range were generalists, all of them infecting fish at the larval/subadult stage, indicating the possible importance of gobies in the life cycle of euryxenous parasites. The absence of adult generalists, particularly ectoparasites with low host specificity, in non-native fish may reflect their generally low abundance in the environment, while an absence of adult endoparasitic generalists was probably related to other factors.

In a recent study, we showed how local-scale climate change impacts (increased temperature, reduced rainfall, shifts in peak rainfall) affected the hydrology of a channelised lowland European river (reduced flow, reduction in flood events, increased siltation, macrophyte growth), allowing native fish species to recolonise the bankside zone and reduce the density of invasive round goby Neogobius melanostomus by effectively removing its preferred habitat, rip-rap bank stabilisation. Here, we report on a follow-on study whereby stretches of the newly vegetated bank were stripped back to clean rip-rap to assess whether presence/absence of rip-rap was the major factor affecting non-gobiid, tubenose goby Proterorhinus semilunaris and round goby abundance. Our results confirmed rip-rap as a major factor increasing round goby abundance, and hence invasion success, on European rivers, while vegetated banks saw an increase in the abundance and diversity of non-gobiid species. While tubenose gobies showed no preference for habitat type, their numbers were significantly reduced in rip-rap colonised by larger and more aggressive round gobies. We discuss our results in light of recent artificial bank restoration measures undertaken on the Danube and Rhine and the potential role of round goby as a flagship species for cost-effective, large scale river bank restoration projects with multiple ecosystem benefits.

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 Černá 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.

The round goby, Neogobius melanostomus, is a Ponto-Caspian fish species currently found in many parts of Europe, including the North Sea riverine deltas. The objective of this study was to examine the parasite community of fish caught in the lower Elbe (Süderelbe – tidal zone; Geesthacht – non-tidal) in Germany and compare it with published data from the upper Elbe (Ústí nad Labem) in the Czech Republic. Twelve parasite taxa were recorded in the lower Elbe, six in the Süderelbe and nine near the city of Geesthacht. Süderelbe fish were mainly infected with Angullicola crassus larvae, while gobies from Geesthacht – with glochidia and sporadically occurring Pomporhynchus laevis, and the opposite situation was observed at Ústí nad Labem. It appears that a large tidal weir at Geesthacht significantly contributes to the division of the round goby population, with the Geesthacht parasite community being more similar to that at Ústí nad Labem than the one from the Süderelbe, thus increasing the likelihood that shipping from Hamburg was the introduction vector to Ústí nad Labem. We also recorded Acanthocephalus rhinensis in the Elbe for the first time, and in a new host – the round goby. Thus, round gobies may represent a new vector for the introduction of this parasite along the Elbe.

In this study, we assessed concentrations of 13 trace metals in the scales of Notothenia coriiceps, Trematomus bernacchii and Gobionotothen gibberifrons caught off the coast of James Ross Island (Antarctic Peninsula). Overall, our results for scales broadly match those of previous studies using different fish and different organs, with most metals found at trace levels and manganese, aluminium, iron and zinc occurring at high levels in all species. This suggests that scales can serve as a useful, non-invasive bioindicator of long-term contamination in Antarctic fishes. High accumulation of manganese, aluminium, iron and zinc is largely due to high levels in sediments associated with nearby active volcanic sites. Manganese, vanadium and aluminium showed significant positive bioaccumulation in T. bernacchii (along with non-significant positive accumulation of iron, zinc, cobalt and chromium), most likely due to greater dietary specialisation on sediment feeding benthic prey and higher trophic species. Levels of significance in bioaccumulation regressions were strongly affected by large-scale variation in the data, driven largely by individual differences in diet and/or changes in habitat use and sex differences associated with life stage and reproductive status. Increased levels of both airborne deposition and precipitation and meltwater runoff associated with climate change may be further adding to the already high levels of manganese, aluminium, iron and zinc in Antarctic Peninsula sediments. Further long-term studies are encouraged to elucidate mechanisms of uptake (especially for aluminium and iron) and possible intra- and interspecific impacts of climate change on the delicate Antarctic food web.

Parasitism of monkey goby, Neogobius fliviatilis, was assessed at three brackish water localities with different salinity levels (Gulf of Odessa, Khadzibey Estuary, Lake Kytay) and one freshwater site along the Lower Danube River (Vidin). A total of 25 parasite taxa were identified, with minimum parasite richness recorded in the Khadzhibey Estuary (three species) and the maximum along the Lower Danube (11 species). Parasite richness in the mesohaline Gulf of Odessa and oligohaline Lake Kytay was lower, but still relatively high compared to the Khadzibey Estuary. Our study indicates that freshwater populations of monkey goby host richer and more abundant parasite communities than those inhabiting brackish waters with (more or less) stable salinity. Unstable abiotic conditions that probably affected the parasite’s intermediate hosts contributed to the reduction in parasite species in the estuarine zone of the Danube.

The western tubenose goby Proterorhinus semilunaris, an invasive Ponto-Caspian fish species, has established populations in a wide range of habitat types in the Dyje/Morava river basin (Danube basin; Czech Republic). In this study, we assessed tubenose goby tolerance to environmental variables potentially contributing to its spread and performance in new habitats. Of the seven aquatic habitats examined (lowland rivers, brooks, backwaters, oxbow lakes, borrow pits, reservoirs and carp aquaculture ponds), all except small brooks proved suitable for survival and reproduction, with habitat size the only limiting factor. Diet analysis indicated chironomid larvae as preferred prey, though tubenose gobies were able to switch to other food items under specific conditions (e.g. high macrozoobenthos density), suggesting feeding plasticity. Fish condition was positively correlated with individual diet range, but not with parasite burden. Eighteen metazoan parasite taxa were identified, greatly exceeding the known parasite fauna from the species’ native range. Parasite species richness decreased significantly with fish host dominance. Foraging plasticity, the ability to occupy different habitats and cope with parasitism observed in this study all may have important implications for tubenose goby dispersal success and invasiveness.

This study focused on the total mercury content in fish from seven drinking-water reservoirs located in the Morava River Basin: Bojkovice, Boskovice, Hubenov, Karolinka, Landstejn, Ludkovice and Nova Rise in the Czech Republic. A total of 308 fish were collected for the analysis. The content of total mercury was measured in the muscle tissue of bream, roach and perch using atomic absorption spectrometry and varied from 0.057±0.009 to 0.440 mg kg−1 in bream, from 0.030±0.005 to 0.393±0.138 mg kg−1 in roach and from 0.092±0.007 to 0.638±0.042 mg kg−1 in perch. The highest total mercury content was found in perch from Landstejn and the lowest was measured in roach from Ludkovice. A positive statistically significant relationship was found between fish weight and total mercury content in fish muscle for almost all species and all sampling sites, except for roach from Ludkovice. A total of 19 samples exceeded the maximum mercury level set by legislation on food contaminants—0.5 mg kg−1 in freshwater fish.

In this study, we provide a descriptive assessment of how chemical and hydro-morphological stressors have affected the fish community along one of the most impacted rivers in Central Europe. In addition to the toxicity of combined pollutants (expressed in toxic units), a range of hydro-morphological characteristics were measured to assess which stressors have had an impact. No longitudinal spatial trend was observed in fish assemblage characteristics as individual sites were affected by different stressors. Instead, five largely artificial assemblage “zones” were identified corresponding to different combinations of stressors. Water quality (principally dissolved O2) and hydromorphology were the main drivers affecting fish presence and density, with self-purification processes, restocking from tributaries and geomorphology promoting fish survival and/or recovery, despite increasing toxic pressure downstream. Our results suggest that a) toxic units alone are insufficient to establish causative factors in fish community loss as they do not take account of hydro-morphological stressors, many of which interact with and/or mask each other, and b) that a single WFD monitoring site in such heavily impacted rivers is insufficient to assess ecological status; rather, the ecological status of specific “zones” (identified based on fish assemblage structure, habitat and water quality) should be assessed, with the ultimate aim of merging the zones and returning the river to a single functioning longitudinal ecosystem, accepting that this is unlikely to resemble the natural pre-industrial status of the river.

Large lowland rivers and their alluvial floodplains comprise a wide range of biotopes inhabited by many animal and plant species (Adamek and Sukop 1992; Schiemer 1999; Schomaker and Wolter 2011). The lotic systems are highly dynamic, supported by a high ability to recover former, and to create new, biotopes. Natural, non-impacted lowland streams display a rich and diverse lateral and longitudinal zonation of river and alluvial biotopes, with good hydrological and ecological interconnection of pools, riffles, side arms and oxbow lakes, riparian wetlands, flooded meadows and wooded alluvial land.

Myxobolus pseudodispar Gorbunova, 1936 (Myxozoa) was originally described as a parasite of common roach, Rutilus rutilus (Linnaeus), with developing stages in muscles and spores disseminated in macrophage centres of different organs and tissues. Later, this parasite was described from several other cyprinids, but with relatively large intraspecific differences based on SSU rDNA gene sequences. Within our long-term study on myxozoan biodiversity, we performed a broad microscopic and molecular screening of various freshwater fish species (over 450 specimens, 36 species) from different localities. We investigated the cryptic species status of M. pseudodispar. Our analysis revealed four new unique SSU rDNA sequences of M. pseudodispar as well as an infection in new fish host species. Myxobolus pseudodispar sequence analysis showed clear phylogenetic grouping according to fish host criterion forming 13 well-recognised clades. Using 1% SSU rDNA-based genetic distance criterion, at least ten new species of Myxobolus Butschli, 1882 may be recognised in the group of M. pseudodispar sequences. Our analysis showed the paraphyletic character of M. pseudodispar sequences and the statistical tests rejected hypothetical tree topology with the monophyletic status of the M. pseudodispar group. Myxobolus pseudodispar represents a species complex and it is a typical example of myxozoan hidden diversity phenomenon confirming myxozoans as an evolutionary very successful group of parasites with a great ability to adapt to a new hosts with subsequent speciation events.

Ergasilosis is a common parasitic disease of fish caused by species of the family Ergasilidae. During the fish growing season, parasitic abundance (including developmental stages) changes in relation to zooplankton development. In this study, we evaluated the seasonal dynamics of ergasilosis in relation to zooplankton development at two reservoirs (Hubenov, Koryčany) in the Morava River Basin (Czech Republic). Samples of fish and zooplankton were obtained at monthly intervals between April and October 2014. In total, 189 fish of 11 species were caught using electrofishing and seine nets. Overall, epidemiological characteristics were higher in the Hubenov reservoir, which also hosted higher numbers of pelagic Copepods. Hubenov also supported a higher number of predatory fish species, which presumably helped to reduce the number of zooplanktonophagic cyprinids. Our results suggest that each reservoir represents a unique ecosystem with its own pattern of ergasilosis seasonal development. Differences between reservoirs are closely related to zooplankton development, which is in turn affected by the fish stock in each reservoir. As the nauplius and copepod stages of arthropods form part of the zooplankton assemblage, they will be found at highest numbers in reservoirs where predatory fish suppress zooplanktonophagic fish species. We suggest to analyse zooplankton with the determination of the genus Ergasilus.

As invaders of European and North American aquatic systems, Ponto–Caspian gobiids are believed to represent a significant negative threat to native fish assemblages and cottid species in particular. To date, relatively few studies have tried to document actual impacts, most being short-term and/or laboratory based. Here, we examine 8 years (2008–2015) of electrofishing data from a 1200-m stretch of rip-rap along the Austrian Danube, initiated following establishment of four non-native gobiids: tubenose goby Proterorhinus semilunaris, bighead goby Ponticola kessleri, racer goby Babka gymnotrachelus and round goby Neogobius melanostomus. While we registered 26 fish species in total, most native species were caught along the rip-rap only occasionally. Only native bullhead Cottus gobio and the four non-native gobiids were caught regularly. Although cottids are presently believed to be most vulnerable to gobiid invasion, we observed no negative trend in bullhead abundance over the 8-year dataset, the population remaining stable and at similar abundances to gobiids. While we observed no significant trend in round, racer or tubenose goby abundance, bighead goby showed a continuous decline. Our data contradict previous reports of drastic impacts on cottid abundance by gobiids (mainly round goby), suggesting potential region-specific effects following invasion.

The parasite communities of three gudgeon species (Gobio gobio, Romanogobio belingi and R. vladykovi) were studied in two widely-separated rivers in the Czech Republic (Central Europe), the Bilina River (North Sea drainage) and Velicka River (Black Sea drainage). Of the 25 parasite taxa identified, 21 species parasitised G. gobio, 8 species R. belingi and 13 species R. vladykovi. Due to the absence of specialist parasites, differences in the parasite community were mainly determined by the ecological conditions prevalent at the locality, which resulted in an increased similarity between sympatric species rather than between allopatric populations of the same species, i.e. G. gobio. Discriminant analysis showed significant differences between the four gudgeon populations. Five parasite species had significant power to discriminate particular parasite communities: the autogenic ectoparasites Gyrodactylus gobiensis, G. markakulensis and Paradiplozoon homoion; the allogenic endoparasite Metorchis xanthosomus and the autogenic endoparasite Acanthocephalus anguillae. Only G. markakulensis occurred in both allopatric populations of G. gobio. Sympatric gudgeon populations were discriminated mainly by the presence of autogenic parasites, especially those with direct life cycles. Differences in parasite infection level between G. gobio and representatives of Romanogobio may reflect variance in diet and/or habitat use. Allopatric populations differed in the number of allogenic parasite species, which were more frequent in the Velicka. Finally, the parasite community of R. belingi from the upper Elbe basin was characterised by a lack of gudgeon specific parasites, possibly supporting its non-indigenous status.

Between 2012 and 2013, we estimated predation of non-native Ponto-Caspian gobies by native piscivores in a European mid-sized lowland river by analysing 268 digestive tracts from six native species: perch Perca fluviatilis, burbot Lota iota, European catfish Silurus glanis, pike Esox lucius, Volga zander Sander volgensis and European zander S lucioperca. Species closely associated with the rip-rap bank had a higher proportion of gobies in their diet (burbot 66 % weight proportion [%m], >= 1+ perch 53 %m, = 1+ perch showed positive selection for tubenose goby Proterorhinus semilunaris, while burbot and pike showed a preference for round goby Neogobius melanostonius, though the values may have been affected by the relatively low sample sizes. We estimate that predators consumed approximately 52 % of goby biomass over our study stretch each year (burbot 41%

The Chinese sleeper (Perccottus glenii), an invasive Asian fish, was first registered in Germany in 2009 (westernmost extent of its invasive range). We sampled Chinese sleepers from two localities on the Bücherlgraben creek (a tributary of the River Naab) in south-eastern Germany in November 2015 and examined them for parasite infection. Twelve taxa were registered, including ciliates (unidentified Trichodina), a monogenean, three cestode species, two digenean taxa, two acanthocephalan species, two nematode species and one mollusc glochidia. Infracommunities consisted of 1–5 species, with 10% of fish uninfected. Three parasite species (Acanthocephalus anguillae, Gyrodactylus luciopercae and Pseudocapillaria tomentosa) were recorded on Chinese sleepers for the first time. The results highlight the important role of the Chinese sleeper as a second intermediate host in the life cycle of heron and grebe parasites. The Chinese sleeper parasite community displayed low homogeneity at both localities sampled, with allogenic parasites (metacercariae and mesocercoids) mostly shared. Differences between localities were mainly caused by autogenic parasites. No invasive parasites associated with the Chinese sleeper were observed in the study area, all parasites being representatives of European fauna. This supports the hypothesis of introduction via the aquarium trade or through transport with commercial fish.

A combination of radio telemetry and electrofishing was used to assess seasonal feeding activity and habitat utilisation of common carp (Cyprinus carpio) in a large (130 ha) semi-intensive aquaculture pond receiving supplementary feed. While telemetry indicated no difference in fish habitat utilisation by size, age or sample year, all fish showed a strong preference for the supplementary feed area (SFA) during the feeding period, electrofishing indicating a 15× higher fish concentration. Despite this, not all of the feed provided was eaten immediately. Carp activity was more evenly spread over the pond in summer/autumn and more concentrated at the SFA in spring. There was a significant shift to deeper waters in winter. Diet analysis indicated a high preponderance of cereal in SFA fish, with natural food (mainly zooplankton) dominant at natural feeding areas. The proportion of ‘emergency’ food (e.g. detritus) was similar in both areas, as was the index of gut fullness. Our results confirm that concentrated and repeated supplementary feeding in one area results in aggregation of carp, potentially leading to uneven population growth and flesh quality and reduced water quality from turbidity and increased nutrient input. As an alternative, we suggest spreading less supplemental feed over a greater area at wider time intervals. This would ensure (a) full utilisation of feed, reducing costs and increasing water quality, and (b) more homogenous fish distribution, ensuring more efficient use of natural food, reduced turbidity, more homogenous size/weight distribution and improved product quality.

One of the main assumed impacts of invasive gobies is predation on benthic macroinvertebrates. Despite numerous dietary studies, however, quantitative evaluations of impact in European river systems are scarce. Here, we investigate the impact of tubenose (Proterorhinus semilunaris, Heckel 1837) and round (Neogobius melanostomus, Pallas 1814) gobies on macroinvertebrates in a lowland river (River Dyje, Czech Republic) by allowing and preventing gobiid access to rip-rap substrate naturally colonised by invertebrates at two sites (Site 1—tubenose goby only, Site 2—tubenose and round gobies). Gobies had a negative impact on invertebrates at both sites, with overall invertebrate density reduced by 15% (ca. 17.9 g m−2 per year) at Site 1 and 36% (ca. 23.6 g m−2 per year) at Site 2. Both species showed increased impact in summer and ingested larger invertebrates preferentially, resulting in an overall reduction in invertebrate body size. Tubenose gobies had a significant impact on Annelida, Gastropoda, Crustacea and Ephemeroptera nymphs, while tubenose and round goby together impacted Annelida, Bivalvia (Dreissena), Gastropoda, Crustacea, Ephemeroptera nymphs, Odonata nymphs and Chironomidae larvae. Our results confirm that round and tubenose gobies can have a significant negative impact on aquatic invertebrate density and community composition.

Summary 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.

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.

Summary Introduction of an exotic species has the potential to alter interactions between fish and bivalves; yet our knowledge in this field is limited, not least by lack of studies involving fish early life stages (ELS). Here, for the first time, we examine glochidial infection of fish ELS by native and exotic bivalves in a system recently colonised by two exotic gobiid species (round goby Neogobius melanostomus, tubenose goby Proterorhinus semilunaris) and the exotic Chinese pond mussel Anodonta woodiana. The ELS of native fish were only rarely infected by native glochidia. By contrast, exotic fish displayed significantly higher native glochidia prevalence and mean intensity of infection than native fish (17 versus 2% and 3.3 versus 1.4 respectively), inferring potential for a parasite spillback/dilution effect. Exotic fish also displayed a higher parasitic load for exotic glochidia, inferring potential for invasional meltdown. Compared to native fish, presence of gobiids increased the total number of glochidia transported downstream on drifting fish by approximately 900%. We show that gobiid ELS are a novel, numerous and ‘attractive’ resource for unionid glochidia. As such, unionids could negatively affect gobiid recruitment through infection-related mortality of gobiid ELS and/or reinforce downstream unionid populations through transport on drifting gobiid ELS. These implications go beyond what is suggested in studies of older life stages, thereby stressing the importance of an holistic ontogenetic approach in ecological studies.

This study presents data on fish assemblage structure for the relatively pristine and understudied Antarctic coastal zone (5-25 m). A total of 545 Notothenioidei and Bathydraconidae fish (eight species) were caught in the Prince Gustav Channel (James Ross Island, eastern Antarctic Peninsula) using Nordic multi-mesh benthic gill nets between January and February 2014. Trematomus hansoni dominated at 5 m and T. bernacchii at 15 m, with Gobionotothen gibberifrons and T. newnesi subdominant. Dominance at 25 m resembled that at 15 m. Despite relatively low numbers, species richness, abundance and biomass appeared to increase with depth. While T. bernacchii, T. hansoni, G. gibberifrons and Notothenia coriiceps all displayed multiple size (and probably age) groups, most T. newnesi ranged between 10-15 cm. Sub-samples of G. gibberifrons and T. bernacchii showed a 1:1 adult/immature ratio, with minimum adult and maximum immature length/weight overlapping. Females outnumbered males, with a ratio of 2.8:1 for G. gibberifrons and 4.8:1 for T. bernacchii. The diet comprised mostly benthic taxa (isopods, gammarids, gastropods, polychaete worms). While G. gibberifrons appeared opportunistic, T. bernacchii specialised more on isopods. Our results highlight the possible importance of the Antarctic inshore zone as feeding habitat; despite frequent ice cover/scouring. We suggest that recent prolonged summer ice cover over the eastern side of the Antarctic Peninsula could have important impacts on inshore fish communities and food webs, though further in-depth studies are needed to confirm our results.

The improvement of water quality in recreational and drinking water reservoirs has been a main priority of river basin authorities for some time. One measure commonly applied is biomanipulation, which aims to improve water quality by adjusting fish community structure. Effective reduction of cyprinid density, with a resultant increase in filtering zooplankton development, has already proved successful in many lakes. In this paper, we document progress in a project to evaluate the feasibility and efficiency of biomanipulation through parallel use of age-selective fish removal and predator stocking to improve water quality in a 42 ha drinking water reservoir. Between 2009 and 2012, cyprinid and young perch ( Perca fluviatilis ) density was reduced through removal of early-stage planktonophagous fish and perch eggs, along with removal of adult bream ( Abramis brama ) and roach ( Rutilus rutilus ) during spawning. Predatory fish were also stocked to increase juvenile mortality of the target species. As a result, cyprinid biomass was significantly reduced (ca. 2/3 of adult bream removed; biomass now estimated at −1 ). This study showed that biomanipulation was successful at the reservoir and that it is a feasible method for other water bodies of similar area and depth with suitable capture sites. While reduced cyprinid biomass has resulted in a continuous increase in zooplankton density and biomass, however, phytoplankton dynamics appear to be dependent on additional factors such as nutrient input (especially phosphorus). Over the coming years, therefore, attention will focus on both external (catchment) and internal (sediment) nutrient sources, in addition to continuing fish biomanipulation.

Background. The life-history traits of non-native species are believed to change in a predictable manner in relation to time since introduction, with populations in the early stages of establishment predicted to invest more energy into reproduction than long-established populations, mainly due to lower intraspecific competition for resources. In Europe, the range of non-native pumpkinseed, Lepomis gibbosus (Linnaeus, 1758), continues to increase. Despite this, the majority of hitherto conducted studies have investigated long-established populations only, very few focusing on newly established populations (

In this study, we examine multiple trophic levels in two Central European rivers (the Dyje and Elbe) to assess whether round goby invasion has changed the pattern of total mercury (Hg) transfer through trophic levels. In the absence of comparable historical data, we also examined levels for European gudgeon, a native benthic species occupying a similar trophic niche to round goby. Our data clearly indicated bioaccumulation of total Hg with increasing trophic position in both rivers. Patterns were very similar in both rivers, with no significant difference in total Hg accumulation between round goby and gudgeon. Biomagnification factors were high for gobies (highest in the Elbe) and relatively low for perch (higher in the Dyje), with levels for burbot (Dyje only) similar to those for gobies. Goby dietary analysis revealed a clear preference for benthic macroinvertebrates in both rivers, with zebra mussels taken only occasionally. Both perch and burbot had an omnivorous diet, effectively “diluting” total Hg accumulation from benthivorous fish. Our results indicate that goby invasion has not altered the pattern of trophic contaminant transfer and, consequently, has not increased threat levels to top predators and humans. Our results corroborate findings from around Europe suggesting a preference for macroinvertebrates over zebra mussels and provide further evidence for case-specificity regarding potential round goby impacts on recipient systems.

The parasitic copepod Neoergasilus japonicus (Harada, 1930) (Ergasilidae), native to east Asia, is widely distributed in Asia, Europe, and North and Central America. Recently, this species appeared in lentic water bodies of the River Dyje floodplain (Danube basin, Czech Republic). It was first recorded in 2015 and in 2 years it reached a 100% prevalence in recently expanding non-native fish host, Lepomis gibbosus (Linnaeus, 1758) (Centrarchidae, native to North America) at two borrow pits. Abundance of N. japonicus increased with fish length, with maximum intensity of infection reaching 99 parasites per fish. The parasite was most frequently found attached to the dorsal and anal fins of fish, while preference for the dorsal fin was more evident with lower infection intensities. Utilization of expanding fish hosts in water bodies that are regularly interconnected via natural or managed flooding may support the rapid dispersal of this non-native parasite.

Metazoan parasite communities ofLepomis gibbosus(Centrarchidae), one of the most successfully introduced fish species in Europe, were studied at two isolated ponds (Knielingen, Tropfen) along the Upper Rhine in Germany. Nine parasite taxa were observed, including North American species co-introduced to Europe (ancyrocephalid monogeneans, diplostomid trematodes), circumpolar species infectingL. gibbosusin both their native and non-native ranges (bothriocephalid cestodes) and locally acquired parasitic nematodes. Both parasite communities consisted predominantly of North American species. Acquisition of local parasites was not observed at Tropfen, where the fish community comprised just two species, withL. gibbosusdominant. Low prevalence and abundance of acquired parasites was found at Knielingen, which supported a diverse fish community. At Tropfen, a high abundance of the North American parasitePosthodiplostomum centrarchiprobably contributed to the lower condition index, hepatomegaly and splenomegaly observed. Due to low local parasite competency,L. gibbosusappears to have no significant impact on parasite dynamics in affected habitats.

Recent studies have confirmed historic atmospheric deposition of uranium in Antarctica, with a steep and significant increase in levels deposited since the 1980s in Antarctic Peninsula ice core samples. To date, however, there has been little or no attention paid to uranium in the Antarctic food web. Here, we present results for uranium content in scales of three common nototheniid species (Trematomus bernacchii, Gobionotothen gibberifrons, Notothenia coriiceps) from coastal waters off James Ross Island (Antarctic Peninsula). While mean total uranium levels (mean ± SD) were low and similar between species (N. coriiceps 0.08 μg g−1 ± 0.01, T. bernacchii 0.17 μg g−1 ± 0.10; G. gibberifrons 0.11 μg g−1 ± 0.04), linear regressions against standard length indicated bioaccumulation in T. bernacchii (ANOVA, F = 7.8349, P = 0.0076). We suggest this may be the result of dietary specialisation on prey with calcareous shells that accumulate uranium. To the best of our knowledge, this paper provides the first quantitative baseline data on uranium levels in coastal Antarctic nototheniids. While the low levels recorded are unlikely to represent a threat within the food chain, we suggest that further long-term trophic studies (including stable isotope analysis) are needed, recognising that the feeding ecology of individual species (and even individuals) can have a strong effect on overall trends.

In recent decades, gobiid species have increased their distribution throughout Europe and now often represent the dominant genus along many rivers and canals. In this study, we assessed the role of tubenose goby (Proterorhinus semilunaris) as a prey species of native perch (Perca fluviatilis) in a lowland reservoir soon after their initial introduction in 1994 (sampling started 1998) and 17 years after establishment (2011–2012). We compare these data with perch diet composition from before introduction (1981–1982). Our data indicate that tubenose gobies quickly became the dominant species along the reservoir bankside, making them an attractive prey for ≥1 + perch. There was a clear increasing trend in the numbers of larger perch caught along the rip-rap, with the largest fish clearly specialising on gobies. As such, introduction of tubenose gobies has had a pronounced effect on food web and population dynamics along the littoral zone. While goby numbers appear to have dropped significantly in recent years, apparently due to predation pressure, further studies are needed to assess whether such changes have had any general impact on population and food web dynamics within the reservoir.

Brno Reservoir (259 ha) is one of the most intensively utilised waterbodies in the Czech Republic, being used simultaneously for recreation, sport, fisheries, boating and electric power production. Despite this, no consistent fish survey has yet been performed at the reservoir. Between 2009 and 2012, a number of measures, including fish biomanipulation, were applied to improve water quality. Large cyprinids (mainly common bream Abramis brama) were removed and predatory fish (e.g. pike Esox lucius, zander Sander lucioperca) stocked. In September 2012 and 2013, we carried out an extensive study of the fish community in order to describe the present fish assemblage and evaluate the success of biomanipulation. Fish were sampled at 11 locations using electrofishing (inlet zone) and beach seining (lake zone). Twenty-three species and one hybrid were recorded (inlet zone — 20, lake zone — 14), with roach Rutilus rutilus and bleak Alburnus alburnus (plus perch Perca fluviatilis) dominant in inlet samples, but carp Cyprinus carpio dominant by biomass; and white bream Blicca bjoerkna and roach dominant in the lake zone, both by abundance and biomass. Predatory species represented 14-17 % of biomass in both the inlet and lake zones in both years. The final results of biomanipulation were questionable. While a low proportion of adult bream suggests successful removal, populations of small cyprinids, such as roach and white bream, increased in compensation. There was little evidence for an increase in predatory fish following stocking, probably due to angling pressure. Our results indicate that biomanipulation to improve ecological water quality in reservoirs is unlikely to be successful when they are managed specifically for carp and predator angling.

Round gobies Neogobius melanostomus were observed readily consuming soft tissue from carcasses of larger fishes under both laboratory and field conditions. Consumption normally progressed in a typical sequence, starting with soft and easily accessible tissues such as the eyes, followed by puncture of the abdominal cavity, gut consumption and then muscle consumption. Carcass feeding has not previously been seen in N. melanostomus and has potential consequences for transfer of nutrients and contaminants.

In his reaction to our paper ‘Environment not ‘native-ness’ dictates reproductive trait shifts in Ponto-Cas-pian gobies’ (Konecna et al. 2014), Kovac(‘The fishitself, not only environment, should be considered instudying invasion success’; in press) disagree withwhat he considers a misinterpretation of his theory of‘alternative ontogenies and invasive potential’ (hereinAOIP; Kovac 2010). In doing so, he questions thereliability of our results by criticising our methodol-ogy. We would like to take this opportunity to reactto both these points.Kovac (in press) accuses us of using ‘tests basedon improper methods’. Every method includes somedegree of bias, including those used in our paper, andin every case, their use can and should be questioned.However, while we agree with Kovac that ‘hypothe-ses derived from a theory should always be testedwith proper methods’, we are also convinced that noone can claim the right to state which methods are‘proper’ or ‘improper’ without broad consensus andproper discussion. We refute Kovac’s criticism as wechose our methods carefully to minimise any possiblebias and with due reference to the levels of precisionnormally required in fish reproduction studies. Forexample, as we were unconvinced that the gravimet-ric method was a credible means for determininggobiid fecundity (due to the relatively small mass tobe weighed), we decided to measure every egg in theovary instead as it is more reliable, despite beingmore time-consuming. Further, where we wereunconvinced that a parameter could be measured/determined precisely enough (e.g. size of oocytes inthe last stage of maturation), we omitted it, despitebeing aware that the value of our results might besomewhat decreased thereby (see Kovac in press).Kovac (in press) criticises our method for deter-mining goby fecundity, that is absolute fecundity (F

The western tubenose goby ( Proterorhinus semilunaris) is one of several Ponto-Caspian gobiid species currently extending their distribution range over Europe. As part of an ongoing study, we examined the annual dynamics of an established tubenose goby population from the River Dyje (Czech Republic, Danube basin), 13 years after its first occurrence. Monthly monitoring (February 2011-January 2012) confirmed that the species dominates the local fish assemblage (more than two thirds of fish caught) and is the only species captured every month. The population is female-dominated from March-August and displays a 1:1 sex-ratio from September on. Tubenose gobies in the Dyje are characterised by rapid reproduction and early maturation, with all 0+ fish ready to spawn at the start of the next spawning season. Females display significantly higher GSI but lower body condition and a shorter life-span than males. Female life-span was almost strictly annual, while males were more likely to survive to a second spawning season. This study is unique in presenting results for a tubenose goby population with long-term absence of other potentially competing gobiid species. These results provide new baseline data for future tubenose goby studies in areas both with and without competitors.

Here we report the catching of a single specimen of a rare native fish species, the cactus roach Rutilus virgo (Heckel), by rod and line on 31 January 2016 at Břeclav (r.km 25.6), on the main channel of the River Dyje (right tributary of the River Morava, Danube basin). This report comes 62-years after the last confirmed record in the Czech Republic, the species having been reported as extinct in the country since then. The morphometric and genetic characteristics of the specimen are presented and evaluated in light of the previous report.