Jihlava River Research Articles

Strontium isotopes in human mobility research: BASr proxies in an anthropologically modified landscape

Strontium isotopes in human mobility research: BASr proxies in an anthropologically modified landscape

Senorady/Mohelno – ‘Boleniska’: A strategic position within the landscape with palimpsest of prehistoric occupation

The landscapes of the Mohelno settlement microregion are mostly gently undulating, but also dissected by two deeply incised river valleys – the Oslava River valley in the north and the Jihlava River valley in the south. The western boundary is formed by Zelený kopec (491 m above sea level, while the eastern boundary is marked by Biskoupský kopec (397.3 m above sea level) and Vodanský kopec (397.5 m above sea level). This microregion was settled at different intensities during the whole duration of prehistory. The ‘Boleniska’ elevation is located in the central part of the microregion and forms a strategic point – the entire microregion is visible from this elevation. This elevation comprise of an occupational palimpsest with intensive occupation during three different periods: at the beginning of the Upper Paleolithic (probably more than one techno-complex), the Late Neolithic (Lengyel culture) and at the end of the Eneolithic period (Bell Beaker culture). There is a high density of sites in this microregion from all three periods of interest. A similar settlement pattern (similar topography and cultural sequences) is known from other Moravian microregions. A preliminary testing of the site’s spatial distribution and a visibility analysis support the hypothesis indicating Mohelno – ‘Boleniska’ as a central site within the entire microregion only in the Paleolithic. The number of similar palimpsests composed of Paleolithic, Neolithic and Eneolithic sites is low within the entire microregion and the interpretation of this phenomenon must also take into consideration climatic factors, subsistence strategies, and socio-economic conditions in future research.

Příspěvek k poznání vodních měkkýšů Jihlavy [A contribution to the knowledge of aquatic molluscs of the Jihlava River

This paper presents results of a malacological survey of the middle and upper section of the Jihlava River, a tributary of the Dyje River (Czech Republic). Twenty-three species of aquatic molluscs (13 gastropods, 10 bivalves) were found at 35 sites during research realised mostly in 2017 and 2020. In comparison with the lower section of the Jihlava River, a significantly lower proportion of bivalves of the family Unionidae was found in the middle and upper sections.

Vodní měkkýši Oslavy [Aquatic molluscs of the Oslava River

This paper presents results of a malacological survey of the Oslava River, a tributary of the Jihlava River (Czech Republic, Southeastern Moravia). Sixteen species of aquatic molluscs (8 gastropods, 8 bivalves) were found at 14 sites during the research conducted from 2010 to 2018. The research was focused on the endangered bivalve Unio crassus. Its population was confirmed at the lower river section and is connected with the population in the Jihlava River.

Extent of the Jihlava River sediments load by geogenic elements

Extent of the Jihlava River sediments load by geogenic elements

Comparison of balance of tritium activity in waste water from nuclear power plants and at selected monitoring sites in the Vltava River, Elbe River and Jihlava (Dyje) River catchments in the Czech Republic

During the routine operation, nuclear power plants discharge waste water containing a certain amount of radioactivity, whose main component is the artificial radionuclide tritium. The amounts of tritium released into the environment are kept within the legal requirements, which minimize the noxious effects of radioactivity, but the activity concentration is well measurable in surface water of the recipient. This study compares amount of tritium activity in waste water from nuclear power plants and the tritium activity detected at selected relevant sites of surface water quality monitoring. The situation is assessed in the catchment of the Vltava and Elbe Rivers, affected by the Temelín Nuclear Power Plant as well as in the Jihlava River catchment (the Danube River catchment respectively), where the waste water of the Dukovany Nuclear Power Plant is discharged. The results show a good agreement of the amount of released tritium stated by the power plant operator and the tritium amount detected in the surface water and highlighted the importance of a robust independent monitoring of tritium discharged from a nuclear power plant which could be carried out by water management authorities. The outputs of independent monitoring allow validating the values reported by a polluter and expand opportunities of using tritium as e.g. tracer.

Integration of soil and water conservation measures in an intensively cultivated watershed – a case study of Jihlava river basin (Czech Republic)

Abstract Reduction of nitrogen and phosphorus inputs into surface waters from nonpoint agricultural sources requires targeted application of differentiated measures. In the study focused on soil and water conservation in the Jihlava river basin upstream of the Dalešice reservoir, we identified areas at potential risk of soil erosion, elevated infiltration and nutrient leaching, tile-drained areas and vulnerable riparian zones of water bodies. We then designed a system of complex protective measures for this river basin in more variants, and their effectiveness was estimated using simple empirical model calculations and research findings. Application of the measures defined by optimal variant 3 in the studied watershed could lead to reduction of the soil erosion effects on the surface water quality by 26.5 %, with simultaneous reduction of the amount of washed out total nitrogen by 22.8 %. The results of our study constitute a partial component of the Qualitative Model of the Jihlava River Basin and they were provided for use to the Vysočina Region authorities and the State Land Office.

Sedimentary record and anthropogenic pollution of a complex, multiple source fed dam reservoirs: An example from the Nové Mlýny reservoir, Czech Republic

While numerous studies of dam reservoirs contamination are reported world-wide, we present a missing link in the study of reservoirs sourced from multiple river catchments. In such reservoirs, different point sources of contaminants and variable composition of their sedimentary matrices add to extremely complex geochemical patterns. We studied a unique, step-wise filled Nové Mlýny dam reservoir, Czech Republic, which consists of three interconnected sub-basins. Their source areas are located in units with contrasting geology and different levels and sources of contamination. The aim of this study is to provide an insight into the provenance of the sediment, including lithogenic elements and anthropogenic pollutants, to investigate the sediment dispersal across the reservoir, and to assess the heavy metal pollution in each basin. The study is based on multi-proxy stratigraphic analysis and geochemistry of sediment cores. There is a considerable gradient in the sediment grain size, brightness, MS and geochemistry, which reflects changing hydrodynamic energy conditions and primary pelagic production of CaCO3. The thickness of sediments generally decreases from proximal to distal parts, but underwater currents can accumulate higher amounts of sediments in distal parts near the thalweg line. Average sedimentation rates vary over a wide range from 0.58cm/yr to 2.33cm/yr. In addition, the petrophysical patterns, concentrations of lithogenic elements and their ratios made it possible to identify two main provenance areas, the Dyje River catchment (upper basin) and the Svratka and Jihlava River catchments (middle and lower basin). Enrichment factors (EF) were used for distinguishing the anthropogenic element contribution from the local background levels. We found moderate Zn and Cu pollution (EF ~2 to 5) in the upper basin and Zn, Cu and Pb (EF ~2 to 4.5) in the middle basin with the peak contamination in the late 1980s, indicating that the two basins have different contamination histories.

The valley system of the Jihlava river and Mohelno reservoir with enhanced tritium activities

The Dukovany nuclear power plant (NPP Dukovany) releases liquid effluents, including HTO, to the Mohelno reservoir, located in a deep valley. Significantly enhanced tritium activities were observed in the form of non-exchangeable organically bound tritium in the surrounding biota which lacks direct contact with the water body. This indicates a tritium uptake by plants from air moisture and haze, which is, besides the uptake by roots from soil, one of the most important mechanisms of tritium transfer from environment to plants. Results of a pilot study based on four sampling campaigns in 2011-2015 are presented and discussed, with the aim to provide new information on tritium transport in the Mohelno reservoir - Jihlava River - plants ecosystems.

Zatížení ekosystému středního toku řeky Jihlavy těžkými kovy

Kontaminace svaloviny ryb těžkĂ˝mi kovy představuje potenciĂĄlnĂ­ riziko pro konzumenty ryb. Řeky protĂŠkajĂ­cĂ­ ĂşzemĂ­m s velkĂ˝mi aglomeracemi a silnĂ˝m prĹŻmyslovĂ˝m vyuĹžitĂ­m bĂ˝vajĂ­ často velmi zatĂ­ĹženĂŠ, zvlĂĄĹĄtě rtutĂ­, olovem a kadmiem. Řeka Jihlava protĂŠkĂĄ několika městy s vĂ˝raznou prĹŻmyslovou aktivitou, například Jihlavou a Třebíčí. Tato řeka bĂ˝vala v minulosti často označovĂĄna jako silně znečiĹĄtěnĂĄ, nejvĂ­ce rtutĂ­ v Ăşseku nad vodnĂ­mi dĂ­ly DaleĹĄice a Mohelno.CĂ­lem tohoto sledovĂĄnĂ­ bylo zjiĹĄtěnĂ­ obsahu těžkĂ˝ch kovĹŻ ve svalovině ryb ĹžijĂ­cĂ­ch nad a pod vodnĂ­mi dĂ­ly DaleĹĄice a Mohelno a posouzenĂ­ vlivu těchto vodnĂ­ch děl na Ăşroveň kontaminace ryb. Pro upřesněnĂ­ situace na toku byl zjiĹĄĹĽovĂĄn obsah těžkĂ˝ch kovĹŻ ve vodě, sedimentu dna a zoobentosu na obou lokalitĂĄch.Monitoring byl zaměřen na tyto kovy: Hg, Pb, Cd, Cu, Cr, Ni a Zn. Vzorky vody, sedimentu dna, zoobentosu a rybĂ­ svaloviny byly odebrĂĄny v prĹŻběhu roku 2007 ze dvou lokalit řeky Jihlavy: Vladislav (odběr 15. srpna) nad vodnĂ­mi dĂ­ly DaleĹĄice a Mohelno, nedaleko města Třebíč a HrubĹĄice (odběr 25. května) pod vodnĂ­mi nĂĄdrĹžemi. Vzorky vody byly odebrĂĄny do 1,5 l polyetylenovĂ˝ch lahvĂ­. Vzorky sedimentu dna a zoobentosu byly odebrĂĄny jako směsnĂŠ vzorky napříč lokalitami, dle standardnĂ­ch metodik (EN ISO 27828). Jako ichtyoindikĂĄtor byla zvolena parma obecnĂĄ (Barbus barbus), jelec tlouĹĄĹĽ (Leuciscus cephalus) a pstruh obecnĂ˝ (Salmo trutta m. fario). Vzorky ryb byly zĂ­skĂĄny za pouĹžitĂ­ standardnĂ­ch metod odlovu elektrickĂ˝m agregĂĄtem, sedm jedincĹŻ od kaĹždĂŠho sledovanĂŠho druhu ryb. Svalovina ryb byla odebĂ­rĂĄna individuĂĄlně z levĂŠ hřbetnĂ­ části trupu kaĹždĂŠ ryby bez kĹŻĹže. Obsah sledovanĂ˝ch kovĹŻ byl stanoven na Ústavu chemie a biochemie Mendelovy univerzity v Brně za pouĹžitĂ­ přístrojĹŻ AMA 254, SPECTR AA-30 a AA-300. ZjiĹĄtěnĂŠ vĂ˝sledky byly statisticky vyhodnoceny v programu Unistat 5.1 metodami ANOVA a Tukey HSD (P < 0,05). ZĂ­skanĂŠ vĂ˝sledky byly porovnĂĄny se směrnicĂ­ EU 221/2002/EC, mnoĹžstvĂ­ bezpečně konzumovatelnĂŠ svaloviny ryb bylo vypočítĂĄno za uĹžitĂ­ metodiky WHO (směrnice č. 837).Při porovnĂĄnĂ­ zjiĹĄtěnĂ˝ch koncentracĂ­ jednotlivĂ˝ch kovĹŻ s platnou legislativou (směrnice 2005/78/EC, nařízenĂ­ vlĂĄdy č. 229/2007 Sb., a vyhlĂĄĹĄka č. 305/2004 Sb.) jsme nalezli překročenĂ˝ limit pro obsah rtuti ve vodě (limit 0.1 μg / l). DĂĄle jsme zjistili, Ĺže obsah rtuti ve vodě na lokalitě Vladislav (2.00 μg / l) byl dvakrĂĄt vyĹĄĹĄĂ­ neĹž na lokalitě HrubĹĄice (0.99 μg / l). V sedimentu dna na lokalitě HrubĹĄice byl zjiĹĄtěn vyĹĄĹĄĂ­ obsah niklu neĹž na lokalitě Vladislav, kde bylo naopak vyĹĄĹĄĂ­ mnoĹžstvĂ­ kadmia, olova, chromu a niklu. Obsah rtuti byl na obou lokalitĂĄch podobnĂ˝. Velmi vysokĂ˝ obsah těžkĂ˝ch kovĹŻ v sedimentu znamenĂĄ potenciĂĄlnĂ­ nebezpečí s ohledem na nenadĂĄlĂŠ uvolněnĂ­ během nĂĄhlĂ˝ch změn chemismu vody, zejmĂŠna pH.Z hlediska obsahu jednotlivĂ˝ch kovĹŻ v rybĂ­ svalovině byly zjiĹĄtěny nĂĄsledujĂ­cĂ­ skutečnosti. Na lokalitě Vladislav byl nalezen ve svalovině parmy i tlouĹĄtě statisticky prĹŻkazně vyĹĄĹĄĂ­ obsah Hg (0,155 ± 0,012 mg / kg a 0,163 ± 0,064 mg / kg) oproti lokalitě HrubĹĄice (0,073 ± 0,035 mg / kg a 0,095 ± 0,082 mg / kg). PodobnĂĄ situace byla i v případě kadmia u jelce tlouĹĄtě (0,062 ± 0,140 mg / kg ve Vladislavi a 0,006 ± 0,002 mg / kg v HrubĹĄicĂ­ch), naopak na lokalitě HrubĹĄice byl u parmy zjiĹĄtěn statisticky prĹŻkazně vyĹĄĹĄĂ­ obsah Ni (0,109 ± 0,040 mg / kg) oproti Vladislavi (0,050 ± 0,017 mg / kg). DĂĄle byl u parmy i jelce tlouĹĄtě zjiĹĄtěn statisticky vyĹĄĹĄĂ­ obsah olova na lokalitě HrubĹĄice (0,155 ± 0,048 mg / kg u parmy a 0,182 ± 0,110 mg / kg u tlouĹĄtě) neĹž na lokalitě Vladislav (0,050 ± 0,017 mg / kg a 0,064 ± 0,005 mg / kg). VyĹĄĹĄĂ­ obsah olova ve svalovině ryb pod přehradnĂ­mi nĂĄdrĹžemi DaleĹĄice a Mohelno nekoresponduje s koncentracemi tohoto kovu v sedimentu dna a nĂĄsledně i v zoobentosu, jeĹž jsou v tĂŠto oblasti relativně nĂ­zkĂŠ ve srovnĂĄnĂ­ s lokalitou nad nĂĄdrĹžemi.VĂ˝počet maximĂĄlnĂ­ch tolerovanĂ˝ch mnoĹžstvĂ­ zkonzumovanĂŠ svaloviny ryb dle platnĂ˝ch předpisĹŻ FAO/WHO odhalil, Ĺže na obou lokalitĂĄch byla limitujĂ­cĂ­m prvkem rtuĹĽ. NejniŞťí tolerovanĂŠ mnoĹžstvĂ­ bylo nalezeno v případě jelce tlouĹĄtě a parmy obecnĂŠ na lokalitě Vladislav (1,94 kg a 1,84 kg na osobu tĂ˝dně). V současnĂŠ době, s ohledem na mnoĹžstvĂ­ lovenĂ˝ch ryb v tomto revĂ­ru (v prĹŻměru 90 kusĹŻ jelce tlouĹĄtě o celkovĂŠ hmotnosti 76,30 kg a 35 kusĹŻ parmy obecnĂŠ s celkovou hmotnostĂ­ 51,90 kg ročně) lze konzumaci rybĂ­ svaloviny z těchto lokalit povaĹžovat za relativně bezpečnou, v souvislosti se vzrĹŻstajĂ­cĂ­m rybářskĂ˝m tlakem vĹĄak mĹŻĹže do budoucna znamenat určitĂŠ riziko.

Enhanced activities of organically bound tritium in biota samples

A pilot study aimed on possible occurrence of elevated activity of non-exchangable organically bound tritium (NE-OBT) in biota was performed. The first results showed a significant surplus of NE-OBT activity in biota of the valley of Mohelno reservoir and Jihlava river. The liquid releases of HTO from the nuclear power plant Dukovany is the source of tritium in this area. This area can be a source of various types of natural samples for future studies of tritium pathways.

New records of Compsopogon aeruginosus (Rhodophyta) in rivers of central Europe

Abstract The representatives of the genus Compsopogon Montagne in Bory et Durieaux (Rhodophyta) are basically tropical or subtropical algae. In central Europe they are only found in aquaria and in water bodies affected by thermal effluents, like the species C. aeruginosus (J. Agardh) Kützing in the Pulkau River (Austria), a tributary of the Dyje /Thaya River (Austria, Czech Republic). The first observation of this species was made in 2007 in the Pulkau River. In autumn 2010 the species was also observed at lower densities in an approximately 20 km section of the Dyje/Thaya River between the mouth of the Pulkau River (A) and the Nové Mlýny Reservoir (CR). Recently, the species was found also in Skryjský Brook, a tributary of the Jihlava River, below the cooling water effluent from the Dukovany Nuclear Power Plant, South Moravia, Czech Republic. This is the second finding of representatives of the genus Compsopogon in rivers in central Europe.

Removal of American mink increases the success of simulated nests in linear habitat

Alien species of predators may negatively influence the breeding success of waterfowl. Previous studies have tested whether predator removal causes an increase in nest success and breeding densities; however, conclusions have been contradictory. Here we examine the impact of the removal of introduced American mink, Mustela vison, on the survival of simulated waterfowl nests in two treatment and two control transects, in a linear section of habitat along the Jihlava River, Czech Republic. Nest survival was recorded during two periods (June and July), with minks removed after the first replicate. In total, eight minks were removed from treatment transects. Whereas nest survival in control transects slightly decreased from June to July, the opposite trend, i.e. an increase in nest survival, was apparent in the treatment transects. On the basis of the results, we suggest that a local reduction in mink populations is an effective short-term tool for the conservation of protected waterfowl species. Our study adds to others, reporting potentially adverse effects of alien, introduced, carnivorous species on local biota.

Residual Metal Contamination of the ecosystem in the lower course of the Jihlava River

In November 2001, October and November 2002, the concentrations of Hg, Cd, Pb, Cr, Cu, Zn and Ni were determined in four localities of the lower course of the Jihlava River (Czech Republic). The river water, sediments of the riverbed, zoobenthos and tissues of the fish (gill, gonad, skin, dorsal muscle) were analysed. The chub (Leuciscus cephalus) was used as the ichthyo-indicator. At the same time, the stability of the fish community was evaluated using electrofishing and applying basic ichthyological methods. The work links up with previous investigation of the upper course of the Jihlava River (three localities) carried out by the authors in the same way in 1999. The aim of present study was the completion of previous investigation in the whole longitudinal river profile by monitoring selected heavy metals. The highest Cr (14.290 – 77.070 mg/kg), Zn (13.600 – 92.930 mg/kg) and Ni concentrations (12.290 – 36.680 mg/kg) were found in sediments and their highest loading by all of the monitored metals (without Ni) was detected in the last downstream locality (Pohořelice). Zoobenthos was most contaminated by Zn and Cu (7.480 – 62.690 and 8.050 – 21.810 mg/kg). In the body tissues of the chubs, the highest concentrations of Cd, Hg, Cu, Zn and Ni were determined in the gills, while Pb was also high in gills but also in gonads, the skin and in the muscle tissue. Concentrations of the analysed metals in the chub muscle were (in mg/kg): Hg 0.040 ± 0.014 – 0.133 ± 0.063, Cd 0.003 ± 0.002 – 0.010 ± 0.004, Pb 0.045 ± 0.038 – 0.768 ± 0.038, Cr 0.046 ± 0.023 – 0.106 ± 0.092, Cu 0.203 ± 0.123 – 0.634 ± 0.194, Zn 4.25 ± 0.84 – 6.69 ± 2.95 and Ni 0.062 ± 0.018 – 0.103 ± 0.030. Significant differences in the chub muscle were found concerning Hg, Pb, Cu (P < 0.01) and Cd (P < 0.05). Taking into consideration the actually valid FAO/WHO limits for human consumption of chub muscle from the investigated river section, only Hg (PTWI 2.3 kg in locality 7) and Pb (PTWI 2.0 kg in locality 4) could constitute some risk for human health. The index of diversity of the fish community was 0.825 – 2.110, equitability index 0.380 – 0.793, abundance 312.6 – 2,106.5 fish/ha and biomass 46.7 – 451.5 kg/ha. The water quality was characterized as betamesosaprobic (saprobity index 1.77 – 2.18). The results of the study reveal detailed ecological data concerning heavy metals contamination of the whole Jihlava River ecosystem (water, sediment, zoobenthos, fish). The outcome of this study extends our knowledge about metals accumulation in different fish tissues (gill, gonad, skin and muscle).

Health Status of the Nase (Chondrostoma nasus) in Breeding Farms from the Jihlava River Basin

This study compares two fish farms in the Jihlava River basin that differ mainly in the intensity of rearing of the nase fry and in water sources. During rearing, we observed the health condition of fry from hatching to expedition at the age of one year. Four species of parasites (i.e., Ambiphrya ameiuri, Apiosoma piscicolum, Trichodina sp., Diplostomum spathaceum) were found to infest the fish and Aeromonas hydrophila was isolated by bacterial culture. In both breeding facilities the intensity and prevalence of Ambiphrya ameiuri increased during the summer. The state of health and its development including the recognised infections was similar in both farms. Immunological indicators such as differential white cell count, absolute white cell count and the oxidative burst in autumn were evaluated in the fry samples. Although fry from both farms had similar health condition, the results on immunological indicators show that fry from farm I are more exposed to the effects of stressors. In the next phase, we confronted immunological indicators of fry from farm II and brood fish from the Jihlava River. The results show differences in immunological indicators, which could be caused by a variety of stress factors having different effects on the immune system of these two fish categories. The environment affects greatly the immunity of juvenile as well as brood fish. It reflects in the different levels of immunological indicators in the comparison of fry from two farms as well as in the comparison of fry and brood fish from the river.

Morphotectonic features of the relief in the drainage area of the upper Jihlava River

The results of the morphostructural analysis based on detailed geomorphologic mapping, as well as on analysis of fissures and fault tectonics are presented. The research leads to a deeper knowledge on the geomorphologic evolution of the area.

The Amphipod Gammarus fossarum as a Natural True Intermediate Host of the Nematode Raphidascaris acus

A single third-stage larva of the fish nematode Raphidascaris acus (Bloch, 1779) (body length 1.77 mm) was found in 1 of 775 gammarids Gammarus fossarum Koch examined from the Jihlava River, Czech Republic. This is the first confirmed record of the advanced L, of this species from an invertebrate host, showing that an invertebrate may serve as true intermediate host of this nematode, in addition to lower aquatic vertebrates. Until now, invertebrates have generally been considered as paratenic hosts of the second-stage larvae of R. acus.

Downstream effect of impoundments on stoneflies: Case study of an epipotamal reach of the Jihlava river, Czech Republic

AbstractDifferent habitat types were sampled monthly at a sampling site ca. 12 km downstream from the Dalešice dam on the Jihlava River beginning before impoundment (1976–1978), prior to the addition of heated wastewaters to the reservoir (1984–1985) and from 1987 to 1989. Plecoptera was one of the model groups of macrozoobenthos that significantly responded to changed conditions of flow, temperature and chemistry of river water. There was an increase in species richness (from five to 14 species), species diversity (about double), density and biomass (about 18 to 40 times greater). The study area was originally an epipotamal (barbel) zone with a typical Plecoptera species composition—Perla burmersteriana, Isoperla grammatica, Nemoura cinerea, Leuctra digitata and L. fusca. After river impoundments the investigated reach is a typical metarhithral (grayling) zone. Production of the Plecoptera community in the river reaches affected by the dams increased (riffle, from 1.37 to 23.53; pool, from 0.26 to 6.98 gm−2y−1). It was similar to production in a rhithral (trout or grayling) zone with a typical species composition of rheophilic and cold‐water species (e.g. Perlodes microcephala, Isoperla difformis, I. oxylepis, Siphonoperla torrentium, Amphinemura borealis).The authors thank Professor František Kubiaček from our department, Professor Richard J. Strange, Tennessee University, Knoxville USA, Professor James V. Ward, Colorado State University, Fort Colins USA and an anonymous reviewer for revising the manuscript and numerous helpful suggestions. This final research was supported by grant No. 204/93/2051 from Grant Agency of Czech Republic.

Life history of the nematode Rhabdochona hellichi, a parasite of the barbel in the Jihlava River, Czech Republic

From April 1992 until June 1993, the seasonal dynamics of Rhabdochona hellichi (Srámek, 1901) in its definitive host, the barbel (Barbus barbus), was studied in the Jihlava River (the Danube basin), Czech Republic. The parasite occurred in barbel throughout the year (overall prevalence 93% and intensity of infection 1-1384 [mean 78] nematodes per fish), but there were distinct seasonal fluctuations in prevalence and mean intensity values associated with the parasite's seasonal cycle of maturation. Prevalence was very high (usually 100%) during most months of the year, while lowest values were recorded in August and October. The highest values of mean intensity occurred in April. Both prevalence and mean intensity values increased with the body length of the hosts. The parasite exhibited a distinct annual cycle of maturation with egg-producing females present only from June until August, whereas larvae occurred in barbel mostly from September until April of the next year. Trichopteran (caddis-fly) larvae of the genus Hydropsyche (H. angustipennis and H. pellucidula) were found as natural intermediate hosts of R. hellichi (prevalence 4%, intensity 1-10 nematode larvae). The strictly seasonal maturation of this nematode may be associated with the temperature regime in the locality and seasonal cycles of maturation of its intermediate hosts.

Seasonal occurrence and maturation of Neoechinorhynchus rutili (Acanthocephala) in barbel, Barbus barbus (Pisces), of the Jihlava River, Czech Republic.

From April 1992 until June 1993, the seasonal occurrence and maturation of the acanthocephalan Neoechinorhynchus rutili in its definitive host, the barbel (Barbus barbus), was studied in the Jihlava River (the Danube basin), Czech Republic. The parasite occurred in barbel throughout the year (overall prevalence 84% and intensity of infection 1-533 [mean 25] acanthocephalars per fish), but there were distinct seasonal fluctuations in prevalence and mean intensity values: prevalence attained 100% in February and March, whereas its lowest value was recorded in July; the lowest values of mean intensity occurred in July-August. Both prevalence and mean intensity values distinctly increased with the body length of hosts. The parasite exhibited a distinct annual maturation cycle when egg-producing females were present mainly in the spring and summer (May-July) and, at a lesser extent, also from December to April of the next year. The seasonal maturation of N. rutili appears to be induced principally by the temperature regimen in the locality. N. rutili cystacanths were recovered from larval Sialis lutaria (Megaloptera) (prevalence 6%).