Anodonta Anatina Research Articles

Effects of nitrate nitrogen pollution on Central European unionid bivalves revealed by distributional data and acute toxicity testing

Abstract Studies from Central Europe have shown a relationship between the impaired population status of threatened freshwater mussel species and elevated nitrate nitrogen (N−NO) concentrations in running waters. Causal mechanisms, however, remain unknown, and no experimental data or comprehensive studies involving more species are available, which causes uncertainty in prioritizing conservation actions. This study uses both descriptive and experimental approaches to identify the effects of nitrates on freshwater mussels and demonstrates the need for integrating different research methods for development of conservation strategies for threatened species. Spatial co‐occurrence of five native freshwater mussel species (Anodonta anatina, Pseudanodonta complanata, Unio pictorum, Unio tumidus, Unio crassus) and N−NO concentrations were examined in a 7th‐order river catchment (Lužnice River, Czech Republic) with anthropogenically‐induced increasing N−NO levels and declining populations of these species during the 20th century. Acute toxicity of N−NO was then estimated for artificially reared juveniles of A. anatina and U. crassus using both lethal and sublethal test endpoints. Results showed that the probability of occurrence of all species was significantly reduced in reaches with elevated N−NO levels. In contrast, the results of toxicity testing revealed that the juvenile stages of the two tested species were less sensitive to N−NO than most previously tested freshwater macroinvertebrates. The detected 96‐h median lethal N−NO concentrations were two orders of magnitude higher than the limits derived from distributional data. Despite the probable absence of a direct negative effect of N−NO on freshwater mussel populations, N−NO has potential to be used as an effective indicator of biotope conditions. Identification of causal mechanisms responsible for the observed relationship between unionids and N−NO will require further research. Copyright © 2009 John Wiley & Sons, Ltd.

Identification of gender-associated mitochondrial haplotypes in Anodonta anatina (Bivalvia: Unionidae)

Doubly uniparental inheritance (DUI) of mitochondrial DNA, different from maternal inheritance, is known to occur in five bivalve families (Mytilidae, Veneridae, Unionidae, Margaritiferidae, Hyriidae). DUI involves two types of mitochondrial DNA: F type, inherited from the mother and M type, inherited from the father. Females have only F type mtDNA, males have both types, M type being located in their gonads, F type in their somatic tissues. Among freshwater bivalves known to show DUI, only Anodonta woodiana occurs in Poland. The aim of this study was to ascertain if DUI occurred in another native bivalve, Anodonta anatina, based on DNA sequence of mitochondrial gene of cytochrome oxidase subunit I (cox1). M haplotype was found in male gonads, and F haplotype in somatic tissues of both sexes. Seven sequences were obtained for each F and M haplotypes, 625–709 base pairs long. Variation of 0.2 and 0.3% was found within F and M cox1 sequences, respectively, and 29–32% variation between them.

Assessment of waterborne parasites in Irish river basin districts – use of zebra mussels (Dreissena polymorpha) as bioindicators

The zebra mussel (Dreissena polymorpha) is an abundant and invasive molluscan shellfish species which arrived in Ireland’s river basins in the early 1990’s. Inland and coastal surface waters can be contaminated by human waterborne zoonotic enteropathogens such as Cryptosporidium parvum, Giardia lamblia, Encephalitozoon intestinalis, E. hellem and Enterocytozoon bieneusi originating predominantly from wastewater treatment plant effluents and agricultural runoff. Bivalve species, i.e., the invasive zebra mussel, Mytilus edulis (blue mussel) and Anodonta anatina (duck mussel) were used as sentinels and also as biomonitors of the aforementioned waterborne pathogens at twelve sites located in three Irish river basin districts impacted by pollution related to various water quality pressures. A variety of advanced biomolecular techniques were utilized to assess the presence and concentration of these pathogens in molluscan shellfish. At least one pathogen species was detected in bivalves at each of the twelve sites. Cryptosporidium, implicated in several recent Irish gastrointestinal epidemics, was recorded at all sites subjected to agricultural runoff and at one treated wastewater discharge site, linking source-track directly to animal and human fecal wastes. Overall, the results demonstrated a long-term human enteropathogen contamination of Irish waters with consequent public health risk-factors for drinking water abstraction and water-based recreational activities. The study provided further solid evidence that zebra mussels can recover and concentrate environmentally derived human pathogens and therefore can be used for the sanitary assessment of surface water quality.

Biomonitoring of surface and coastal water for Cryptosporidium, Giardia, and human-virulent microsporidia using molluscan shellfish

Surface inland and coastal waters in Ireland were surveyed for the human waterborne enteropathogens; Cryptosporidium parvum, Giardia lamblia, Encephalitozoon intestinalis, Encephalitozoon hellem, and Enterocytozoon bieneusi by utilizing bivalve mussel species, i.e., Mytilus edulis (blue mussel), Anodonta anatina (duck 'mussel', actually a unionid clam), and the invasive Dreissena polymorpha (zebra mussel) as biomonitors at twelve sites located in three Irish river-basin districts with various water-quality pressures. Biomolecular techniques were utilized to assess the presence and concentration of these pathogens. At least one pathogen species was detected in shellfish at each site. Cryptosporidium, implicated in several recent Irish gastrointestinal epidemics, was recorded at all sites subjected to agricultural runoff and at one sewage discharge site, linking source-track directly to human and animal fecal wastes. G. lamblia was present at eleven of the twelve sites in a range of concentrations. A coastal bay with raw urban sewage discharge was 100% positive for all analyzed enteropathogens. Overall, the results demonstrate long-term human enteropathogen contamination of Irish waters with consequent public-health risk factors for drinking-water abstraction and water-based activities.

Grazing on microcystin-producing and microcystin-free phytoplankters by different filter-feeders: implications for lake restoration

We studied grazing on the green alga Scenedesmus obliquus and the cyanobacterium Planktothrix agardhii (a microcystin-producing and a microcystin- free strain) by three different filter-feeders to compare the efficiency with which these grazers remove Planktothrix from the water. The filterfeeders were two mussel species (the invasive species Dreissena polymorpha and the native Anodonta anatina) and one zooplankton species (Daphnia galeata). On a weight-specific basis, D. galeata had the highest observed clearance rates and A. anatina the lowest. However, D. galeata was only able to feed on Scenedesmus and not on Planktothrix, probably as a consequence of the morphology of Planktothrix (filaments), since neither microcystin-producing nor microcystin-free strains were grazed by Daphnia. Both mussel species were able to graze on Planktothrix, irrespective of microcystin content. Dreissena showed an especially high clearance rate. On an individual basis, however, Anodonta showed the highest clearance rates, which are a consequence of its large biomass. Densities of Anodonta in the field, however, are presently too low to exert a high grazing pressure on the phytoplankton. We suggest therefore that water managers, who may be interested in using filter-feeders as a biomanipulation tool, focus on the improvement of settlement conditions for native bivalves, such as Anodonta, instead of exotic species like Dreissena.

Horizontal and vertical movements of unionid mussels in a lowland river

AbstractFreshwater mussels are important constituents of freshwater ecosystems, yet much of their basic biology remains to be examined. The behavior of 3 species of unionid mussels (Unio tumidus, Unio pictorum, and Anodonta anatina) was examined in the lowland River Spree (Germany). Mussels were marked individually, and their positions on the sediment surface and depth below the sediment surface were recorded weekly between May and October 2004. The average rate of horizontal movement was 11 ± 15 cm/wk (mean ± 1 SD). The direction of the movements seemed erratic; however, a significant net shoreward displacement of ~17 cm, possibly caused by rising water levels, was observed during the study. A surprisingly high percentage of the mussels (74 ± 7%) was burrowed entirely in the sediment to depths as great as 20 cm during the summer. Smaller mussels and individuals not infested by the zebra mussel, Dreissena polymorpha, burrowed deeper in the sediments than larger or infested mussels. Burrowing reduced infes...

Functional response of Anodonta anatina feeding on a green alga and four strains of cyanobacteria, differing in shape, size and toxicity

We studied the functional response of the freshwater unionid bivalve Anodonta anatina, feeding on five phytoplankton strains differing in food quality: the small green alga Scenedesmus obliquus, a toxic and a non-toxic strain of the filamentous cyanobacterium Planktothrix agardhii and a toxic and a non-toxic strain of the coccoid cyanobacterium Microcystis aeruginosa. On S. obliquus, A. anatina had a type II functional response with a maximum mass-specific ingestion rate (IRmax) of 5.24 mg C g DW−1 h−1 and a maximum mass-specific clearance rate (CRmax) of 492 (±38) ml g DW−1 h−1, the highest values for all the phytoplankton strains that were investigated. On toxic and non-toxic P. agardhii filaments, A. anatina also had a type II functional response, but IRmax and CRmax were considerably lower (IRmax 1.90 and 1.56 mg C g DW−1 h−1; CRmax 387 (±97) and 429 (±71) ml g DW−1 h−1, respectively) than on S. obliquus. Toxicity of P. agardhii had no effect on the filtration rate of the mussels. On the non-toxic M. aeruginosa (small coccoid cells), we also observed a type II functional response, although a type I functional response fitted almost as good to these data. For the colonial and toxic M. aeruginosa, a type I functional response fitted best to the data: IR increased linearly with food concentration and CR remained constant. CRmax and IRmax values for the (colonial) toxic M. aeruginosa (383 (±40) ml g DW−1 h−1; 3.7 mg C g DW−1 h−1) demonstrated that A. anatina filtered and ingested this cyanobacterium as good as the other cyanobacterial strains. However, on the non-toxic M. aeruginosa we observed the lowest CRmax of all phytoplankters (246 (±23) ml g DW−1 h−1, whereas IRmax was similar to that on toxic M. aeruginosa. The high maximum ingestion rates on S. obliquus and M. aeruginosa indicate a short handling time of these phytoplankton species. The high clearance rates on S. obliquus, toxic M. aeruginosa and P. agardhii reflect a high effort of the mussels to filter these particles out of the water column at low concentrations. The low clearance rates on non-toxic M. aeruginosa may be explained by the small size and coccoid form of this cyanobacterium, which may have impaired A. anatina to efficiently capture the cells. Although A. anatina had relatively high maximum clearance rates on non-toxic and toxic P. agardhii, this cyanobacterium does not seem to be a good food source, because of the observed high rates of pseudofaeces production and hence low ingestion rates.

Vodní měkkýši přehradní nádrže Slapy (Česká republika) [Aquatic molluscs of the Slapy Reservoir (Czech Republic)

This paper brings a review of a malacological survey of the Slapy Reservoir (Central Bohemia, Czech Republic). This dam water reservoir was built in 1957 on the Vltava River with area 1392 ha, length 44 km, max. deepness 58 m and altitude 270.6 m. Aquatic molluscs at 22 sites were studied from 2005 to 2006. Altogether, 30 species of aquatic molluscs (21 gastropods, 9 bivalves) which represent nearly 40% of the total Czech aquatic mollusc fauna were found despite the absence of littoral vegetation. Bithynia tentaculata, Radix auricularia, R. cf. ampla, Gyraulus albus, Hippeutis complanatus, Sphaerium corneum, Anodonta anatina and surprisingly also vulnerable Anodonta cygnea belong to most frequent molluscs found during this research. Record of near threatened gastropod Viviparus viviparus fill in long gap among its occurrence in the Vltava River downstream of the Slapy Reservoir (last of the dam water reservoirs on the Vltava River) and in tributaries of the Vltava River in Southern Bohemia (Lužnice, Nežárka). Occurrence of four non-native species (Potamopyrgus antipodarum, Physella acuta, Menetus dilatatus, Ferrissia fragilis) were documented.

Bioaccumulation, bioavailability and environmental fate of chlorophenol impurities, polychlorinated hydroxydiphenylethers and their methoxy analogues

The bioaccumulation potential and environmental fate of polychlorinated hydroxydiphenyl ethers (HO-PCDEs; polychlorinated phenoxyphenols, PCPP), the major impurities of chlorophenol formulations and their methoxy analogues (MeO-PCDEs; polychlorinated methoxyanisoles, PCPAs) were investigated. Oligochaete worms (Lumbriculus variegatus) exposed to sediment spiked with a model substance of one HO-hexaCDE (4'-HO-PCDE 161) or its methoxy analogue (4'-MeO-PCDE 161) clearly accumulated the test compounds revealing the potential for environmental risk of HO-PCDEs and MeO-PCDEs. The HO-PCDE tested has earlier been reported as an abundant component in a Finnish chlorophenol formulation (Ky-5) and its methoxy analogue is recognized as an abundant MeO-PCDE in sawmill soil contaminated by the formulation. The occurrence of 4'-HO-PCDE 161 and its methoxy analogue among other HO-PCDEs and MeO-PCDEs in lake mussels (Anodonta piscinalis) incubated in a river contaminated via the manufacture of Ky-5 showed that these compounds are bioavailable and transported in the aquatic environment. Mussel comparison with sediment data pointed to a higher accumulation potential for MeO-PCDEs than for HO-PCDEs. The finding of HO-PCDEs in groundwater samples collected from a groundwater reservoir, which had been contaminated by chlorophenols, points to potential of HO-PCDEs for transport with water in soil.

A possible evolutionary lag in the relationship between freshwater mussels and European bitterling

The coevolutionary dynamics between European bitterlingRhodeus amarusand freshwater unionid mussels, which the former parasitize by laying eggs on their gills, were tested. In a series of experiments fish preferences and mussel responses were compared in parasites and hosts of recent (Europe) and ancient (Asia) sympatry.Rhodeus amarusreadily oviposited on the gills of all mussel species tested. Fish that laid their eggs on the gills of AsianAnodonta woodiana,however, suffered a dramatic reduction in reproductive success compared to fish that oviposited on the gills of European mussels:Unio pictorum,Unio tumidus,Anodonta anatinaandAnodonta cygnea. This difference was the result of egg ejection behaviour by mussels rather than the unsuitability of the internal gill environment for European bitterling embryo development. The ejection response of mussels with a long sympatry with European bitterling was considerably more pronounced than that of mussels with a substantially shorter sympatry. The data support a coevolutionary arms race between bitterling and mussels and point to an evolutionary lag in the relationship betweenR. amarusand its European mussel hosts.

Spatial distribution of oviposition sites determines variance in the reproductive rate of European bitterling (Rhodeus amarus)

AbstractWe investigated reproductive rate in relation to oviposition site distribution and quality in the European bitterling, Rhodeus amarus, a freshwater fish that spawns on the gills of living unionid mussels. In a laboratory experiment male bitterling led females to groups of four mussels at a significantly higher rate than single mussels, irrespective of mussel species. Females spawned significantly more frequently on the gills of mussels in groups than on solitary mussels, and showed a preference for spawning on the gills of Unio pictorum in comparison with Anodonta anatina. In a field experiment the total number of eggs spawned on the gills of four mussels was significantly higher than that of single mussels, though the mean number of eggs per mussel was equivalent within species. There was a significant effect of species on the number of eggs spawned in mussels; U. pictorum and U. tumidus received more eggs than A. anatina and A. cygnea. We discuss these results in the context of mating system evolution.

Cryptosporidium spp. in Freshwater Bivalves in Portugal

RYPTOSPORIDIUM spp. in water has been implicated inseveral human cryptosporidiosis outbreaks (Fayer 2004).Studies on Cryptosporidium oocysts in surface waters are madedifficult by the low concentrations of organisms present due todilution. Since bivalves are filter-feeders oocysts in suspended inwater can be removed by this filtration and the mollusc digestiveenzymes reduce oocyst viability (Freire-Santos et al. 2002). Ifoocysts survive the bivalve digestive tract and are excreted, thedense fecal material containing viable oocysts are expected tosedimenttothebottomoftheriverbed.However,bivalvefiltrationmechanisms can also concentrate Cryptosporidium oocysts pres-ent in the water. Hence it is possible to recover higher numbersof oocysts from the bivalves compared with that recoverable fromsurface waters (Graczyk et al. 2004).Human consumption of freshwater clams and mussels is com-mon in northeast Portugal and in the Tejo and Guadiana riverbasins. These bivalves might be a source of human Cryptospo-ridium infection therefore, it is important to assess the publichealth risks of eating contaminated bivalves. As bivalves can beuseful bioindicators of superficial water contamination (Graczyket al. 2004), we examined clams in Portugal for the presence ofCryptosporidum oocysts examined evaluated considering thatclams can be.MATERIALS AND METHODSThree freshwater bivalves, Anodonta anatina, Unio pictorum,and Corbicula fluminea, were analyzed. Sixteen sampling areas inthe Guadiana river hydrographic basin in southeast Portugal wereselected and the clams were randomly collected by searching andby kick sampling. A total of 55 samples were obtained betweenMay 2003 and June 2005: 69% (24/55) were ofU. pictorium,50%(19/55) were C. fluminea, and 31% (12/55) were A. anatine. Vari-ation in the water levels, turbidity, and unfavourable conditionsprecluded, being able to collect all three species at each samplingarea each time.Gills and the gastrointestinal tracts of each species were dis-sected from three to 15 bivalves (depending on their size) and thetissues were pooled to provide uniform sizes of preparations fromdifferent bivalves. The tissues were homogenized and oocystswere concentrated using a modification of the methods describedby Ritchie (Pereira da Fonseca 2000) and purified by discontinu-ous sucrose density centrifugation. The material collected at theinterface of the two layers with densities of 1,103 and 1,064 waswashed and concentrated into a pellet by centrifugation and thenresuspended in distilled water to a final volume of 1.5ml.Detection of oocysts was performed by direct immunofluores-cent assay(IFA)using themonoclonal antibody(Mab) kitCrypto/Giardia Cel (Cellabs, Brookvale, Australia). The isolated oocystpreparation was incubated with the Mab and observed by fluor-escence microscopy at 400 magnification. The size and shapeof Cryptosporidium oocysts enabled us to distinguish these fromGiardia cysts.Genotyping using 18S suRNA gene probes was performed on47 samples by nested PCR analysis (Xiao et al. 1999). Genom-ic DNA was extracted by the proteinase K method and the QiagenDNA extraction kit. Qiagen, Hilden, Germany. The primers usedwere 5

Burrowing behaviour affects Paraergasilus rylovi abundance in Anodonta piscinalis

Burrowing depth may affect predation rate, feeding ability and reproduction in bivalve clams. We studied the effect of burrowing depth on the abundance of the ergasilid Paraergasilus rylovi in the freshwater bivalve clam Anodonta piscinalis. We transplanted uninfected clams to a lake where they were allowed to choose their preferred burrowing depth, and were exposed naturally to copepodids of the parasite. There was a significant positive correlation between proportionate burrowing depth (PBD) and the abundance of P. rylovi at the end of the 17-day experiment, the deeper-burrowed clams harbouring more P. rylovi. Original PBD (0%, 50%, 100%) did not influence the final PBD or parasite abundance. Clam length affected PBD, smaller clams burrowing deeper, but it did not affect parasite abundance. Infected experimental clams and naturally-burrowed uninfected clams, both originating from the same lake, did not differ in their mean PBD. This indicated that burrowing of the experimental clams affected parasitism rather than the parasites altering burrowing of the clams. In line with the experimental result, we observed a significant positive correlation between PBD and the abundance of P. rylovi also among clams collected from 2 natural A. piscinalis populations.

Effects of aqueous aluminium on four fish ectoparasites

Effects of aqueous aluminium on four species of fish ectoparasites were studied. Fish infected by Gyrodactylus derjavini, G. macronychus and Anodonta anatina glochidia, and free living Argulus foliaceus were exposed to acidic Al-rich water (pH 5.8), acidic Al-poor water (pH 5.8) and control water (pH 6.3). The results showed that aqueous aluminium had a negative effect on the ectoparasites tested, without any apparent negative effect on the fish hosts. The effect of aluminium was dependent on the kind of organism tested. The gyrodactylids were eliminated, while the duck mussel glochidia showed a decrease in abundance when exposed to 200–260 μg Al/l at pH 5.8. The little fish louse showed increased mortality rate when exposed to aluminium. The effects of aluminium on the parasites in the present study confirm the importance of water quality in general, and acidification in particular, for the distribution and population dynamics of ectoparasites in freshwater environments.

Rare and vulnerable species in the mollusc communities in the mining subsidence reservoirs of an industrial area (The Katowicka Upland, Upper Silesia, Southern Poland)

Pollution of the water environment by mining waters is a problem not only in Poland, but worldwide. This study investigated the mollusc communities in seven mining subsidence reservoirs affected by coal mine output (the Katowicka Upland, Upper Silesia, Southern Poland). The objective of the survey was to determine the relationship between the molluscs and their environments and to evaluate the ecological-conservation value of freshwater habitats which support rare and vulnerable molluscs. From 1993 to 2005, 23 mollusc species were recorded. Our result confirmed an invasion by Potamopyrgus antipodarum (Gray, 1843), whose density varied from 2 to 2422 individuals/m 2 in the waters of the Katowicka Upland. A few rare and vulnerable species were found, e.g. Acroloxus lacustris (Linnaeus, 1758), Hippeutis complanatus (Linnaeus, 1758), Ferrissia wautieri (Mirolli, 1960), Anodonta anatina (Linnaeus, 1758), Musculium lacustre (O.F. Müller, 1774) or Pisidium casertanum (Poli, 1791). Principal component analysis showed a positive correlation between mollusc density and pH, the concentration of chlorides, the total hardness, alkalinity and total dissolved solids, and a negative correlation between the number of species and phosphates. Because of the distinctive environmental features of the mining subsidence reservoirs in Czułów, the research area has provided a refuge for wildlife.

Bivalves of the family Unionidae in ox-bow lakes of the Bug River

The occurrence of bivalves of the family Unionidae was analysed in 16 ox-bow lakes of the Bug River (The Bug River Valley Landscape Park) in the years 2003-2005. One to four species were found in 12 of the lakes. Unio pictorum (L.) was the dominating species in 5 and Anodonta anatina (L.) - in 3 lakes. Other frequent species were U. tumidus Philipsson and A. cygnea (L.). U. crassus Philipsson was found in only one of the ox-bow lakes. Most frequent densities noticed were around 10 ind./m 2 and the maximum density was over 200 ind./m 2 .

Mitochondrial DNA-based diagnostic molecular markers for freshwater bivalves

1. Identification of gender-associated mitochondrial haplotypes in Anodonta anatina (Bivalvia: Unionidae) Marianna Soroka Folia Malacologica CrossRef

Príspevok k topografickému výskumu malakofauny okresu Levice [Contribution to the topographic malacological survey in the Levice District, SW Slovakia

The paper brings new information on mollusc distribution of Levice District in southern part of Central Slovakia. The data were obtained from 14 localities, which lie mainly in the vicinity of the Ipeľ River and southern slopes of Štiavnické vrchy Mts. Together 78 mollusc species (50 land species and 28 fresh-water species) were found. From 9 localities a litter sample from 1m² was analyzed for quantitative evaluation of snail assemblages. Malacocoenoses of thermophilous forest mollusc species were determined in the area of Štiavnické vrchy Mts. foothill (localities 2, 7, 8). The species Limacus flavus, Euconulus praticola, Pisidium amnicum and Unio crassus albensis are important from the viewpoint of nature conservation and geographical distribution. Carpathian species Bythinella austriaca, Vestia turgida, Bielzia coerulans and also European forest species Merdigera obscura reach the southern boundary of their natural area of occurrence. Typical for this region are malacocoenoses of xeric biotopes, composed from species of 4–6 ecoelement – Cecilioides acicula, Cepaea vindobonensis, Granaria frumentum, Chondrula tridens, Xerolenta obvia, Truncatellina cylindrica, Cochlicopa lubricella and Monacha cartusiana. High diversity was observed by freshwater malacocoenoses. Anodonta anatina attenuata, A. cygnea solearis, Unio tumidus zelebori, Radix ampla are typical for stagnant water biotopes (abandoned ‘paleopotamon’ side arms). In slow flowing waters of the Ipeľ River beside the common species also rare species like Anisus septemgyratus and Pisidium amnicum were detected. Interesting is also the occurrence of strong population of invasive species of Asian mussel Sinanodonta woodiana, which is known to infiltrate into a number of streams all around Slovakia.

Metazoan parasites of Neogobius fishes in the Slovak section of the River Danube

Summary Metazoan parasites were investigated in three non-native fishes (monkey goby Neogobius fluviatilis, bighead goby Neogobius kessleri and round goby Neogobius melanostomus) collected from the former and current main channel of the River Danube and from the River Hron, Slovakia, in November 2003. Thirteen parasite species were identified: Triaenophorus crassus, Diplostomum sp., Tylodelphys clavata, Metorchis xanthosomus, Nicolla skrjabini, Gyrodactylus proterorhini, Pomphorhynchus laevis, Contracoecum sp., Raphidascaris acus, Anguillicola crassus, Unio tumidus, Anodonta anatina and Pseudoanodonta complanata. The maximum parasite diversity was found in N. fluviatilis. Total parasite abundance was significantly higher in N. kessleri, but no significant differences among sampling sites were observed. Pomphorhynchus laevis and glochidia of Anodonta anatina reached 100% prevalence in N. kessleri in the new channel of the Danube and, in general, these species were also the most prevalent parasites in all three goby species. For endoparasites, gobies served mostly as intermediate (digenean, cestodes and nematodes) or paratenic (acantocephalan and nematodes) hosts. All parasite species found are common parasites in the Middle Danube basin. No parasites specific to Neogobius, known from their native populations, were observed.

Vodní měkkýši Labe mezi Pardubicemi a Hřenskem [Aquatic molluscs of the Elbe River between Pardubice and Hřensko (Czech Republic)

Aquatic molluscs of the Elbe River between Němčice (near Pardubice, Eastern Bohemia, Czech Republic) and Hřensko (Northern Bohemia, Czech Republic) at 27 localities were investigated from 1994 to 2004. Altogether 40 species (24 gastropods, 16 bivalves) from 77 species known on the territory of the Czech Republic were found at sites under study. A gradual invasion of 6 non-native species (Potamopyrgus antipodarum, Physella acuta, Menetus dilatatus, Ferrissia clessiniana, Corbicula fluminea) and an extinction of another species (Theodoxus fluviatilis, Planorbis carinatus, Unio crassus, Pisidium amnicum) were documented in comparison with historical records. Rare mussel Pseudanodonta complanata and rare pea mussel Pisidium moitessierianum were found at several localities under study and these finds document survival of these bivalves in the Elbe River. Molluscan communities of particular localities were most often usually compounded from species Viviparus viviparus (downstream of loc. 9), Bithynia tentaculata, Radix auricularia, Radix ampla, Unio pictorum, Anodonta anatina, Corbicula fluminea (downstream of loc. 8), Sphaerium rivicola (downstream of loc. 7), Sphaerium corneum s. lat., Pisidium supinum, Dreissena polymorpha.