Leuciscus Cephalus Research Articles

Effects of mining activities and municipal wastewaters on element accumulation and integrated biomarker responses of the European chub (Squalius cephalus)

This study aimed to determine concentrations of 29 elements in the gills and liver as well as biomarker response in gills, liver, and blood of European chub from Pek River (exposed to long-term mining activities), and to compare these findings with individuals from Ibar River (influenced by emission of treated municipal wastewater) and Kruščica reservoir (source of drinking water) using inductively-coupled plasma optical emission spectrometry (ICP-OES). The metal pollution index (MPI) was also calculated. Supporting analyses for the detection of the municipal wastewater presence at investigated localities included analyses of microbiological indicators (total coliforms and Escherichia coli) of faecal pollution. We have assessed biomarker responses from molecular to organism level using the condition index, comet assay, micronucleus test, oxidative stress parameters, histopathological alterations, and fluorescence spectroscopy parameters. Multibiomarker analysis was summarized by Integrated Biomarker Response v2 (IBRv2). Among these locations, Kruščica exhibited the lowest, whereas the Pek River displayed the highest values for both categories of indicator bacteria. Due to the porphyry copper ores mining, individuals from Pek River had several times higher Cu concentrations in both gills and liver compared to the other localities which was confirmed by biomarker responses and IBRv2 value. On the contrary, fish from Kruščica reservoir were the least affected by elemental pollution which is also confirmed by low MPI and IBRv2 values. Responses of biomarkers correspond to the elemental accumulation in the liver and gills of the Ibar River are positioned between the Pek River and Kruščica reservoir. Of all the biomarkers analyzed in this study, the condition index was the least sensitive. The results of this study showed that fluorescence spectroscopy may be a method for fast screening of structural changes in gills caused by the pollution burden.

Genetic Variability of Two Evolutionary Distinct Classes of the Acanthocephala Isolated from European Chub from Rivers of the Adriatic and Black Sea Basins in Croatia

Genetic Variability of Two Evolutionary Distinct Classes of the Acanthocephala Isolated from European Chub from Rivers of the Adriatic and Black Sea Basins in Croatia

Parasitism with Protozoa and Monogeneans in Fish from the Natural Waters of Romania.

Parasitism by protozoa and monogenean flatworms in freshwater fish from Romania was studied by collecting and examining samples from two major river systems there: 183 fish from 17 species from the Olt River and its tributaries; and 155 fish from 16 species from the Mureș River and its tributary, Târnava Mare. The average rates of parasitism in the samples from the two rivers and their tributaries were as follows: Ichthyiophthirius multifiliis (2%), Trichodina spp. (21%), Apiosoma spp. (18%), Mixobolus spp. (8%), Dactylogyrus spp. (9%), and Gyrodactylus spp. (10%). The number of parasite species varied from one river to another. I. multifiliis was found in only 3 fish species, Trichodina spp. in 13 species, Glosatella spp. in 6 species, and Mixobollus spp., Dactylogyrus spp., and Gyrodactylus spp. in 7 different species each. The highest number of parasite species (six) were identified in the European chub (Squalius cephalus) and schneider (Alburnoides bipunctatus), which seem more susceptible to parasitic infections. The aquatic environment of these rivers may represent a source of parasites for fish from neighboring countries through which these rivers pass.

The genome sequence of the European chub, Squalius cephalus (Linnaeus, 1758).

We present a genome assembly from an individual Squalius cephalus (the European chub; Chordata; Actinopteri; Cypriniformes; Cyprinidae). The genome sequence is 1,101.9 megabases in span. Most of the assembly is scaffolded into 25 chromosomal pseudomolecules. The mitochondrial genome has also been assembled and is 16.61 kilobases in length.

Microplastics pollution in freshwater fishes in the South of Italy: Characterization, distribution, and correlation with environmental pollutants

In this study, we investigated the presence, abundance, and chemical nature of microplastics (MPs) in the freshwater fish gastrointestinal tract in the South of Italy, and evaluated the possible correlation between MPs and environmental pollutants. Fifty specimens belonging to five species (Scardinius erythrophthalmus, Barbus barbus, Rutilus rubilio, Leuciscus cephalus, Salmo trutta), from twenty sites were collected. MPs chemical feature was identified by means of Attenuated Total Reflection-Fourier Transform Infrared (ATR-FTIR) and Raman microscopy. MPs were represented by 34.86 % fragments, film, and foam (all together MPs) and 65.14 % by fibers (MFs). The mean number of MPs/MFs per fish ranged from 6.25 ± 4.35 in R. rubilio and 2.26 ± 1.94 in B. barbus. The highest number of MPs/MFs per g of GIT was found in R. rubilio (9.07 ± 9.66), and the lowest in S. erythrophthalmus (0.75 ± 0.53). The highest number of MPs/MFs per fish species was found in L. cephalus (16), and the lowest in S. erythrophthalmus (4). Black predominated in every type of plastic debris identified, followed by blue and white, respectively for MFs and MPs. Polyethylene (PE), polyethylene terephthalate (PET), polystyrene (PS), and polypropylene (PP), were the main plastic polymers found. At fish sampling sites, comparing concentrations in soils of potentially toxic elements and persistent organic pollutants with the number of MPs/MFs in fish, a significant correlation was noted with polychlorinated biphenyls (PCBs) and, in particular, with PCB 105, PCB 118, PCB 156, PCB 157, and PCB 167. A strong correlation was also observed with all types of polycyclic aromatic hydrocarbon (PAHs) particularly with benzo(ghi)perylene, dibenz(a,h)anthracene, benzo(b)fluoranthene, benz(a)anthracene, benzo(a)pyrene, and pyrene. The results of this study would be useful to draft management and action plans, promote intervention plans aiming at removing threats to species and habitats, and address ways of renaturalization.

The European Chub (Squalius cephalus) as an indicator of reservoirs pollution and human health risk assessment associated with its consumption

Five reservoirs (Vlasina, Medjuvršje, Zaovine, Perućac, and Garaši) in Serbia were chosen as study sites, which differ by their position, purpose, stages of eutrophication, management policies, and levels of anthropogenic pressure. The objectives of this research were to: determine the concentrations of 26 elements in muscle, gills, and liver of the European chub by inductively-coupled plasma optical emission spectrometry (ICP-OES); determine the concentrations of 17 organochlorine pesticides in fish muscle by gas chromatography with mass spectrometric detection (GC-MS); compare these findings with condition factor (CF) and histopathological (HP) biomarkers; and assess the potential human health risks due to consumption of chub muscle tissue. The highest elemental accumulation was found in the gills. The European chub was not a good indicator of Pb pollution between reservoirs. Concentrations of Hg, As, and Cu were low and did not exceed the proscribed maximum allowed concentrations (MACs). 4,4′-DDE was detected only in individuals from Vlasina, 4,4′-DDD from Perućac and Zaovine, and heptachlor from Zaovine. Low to moderate levels of HP were observed for both gills and liver in all studied reservoirs. HP index for gills was significantly higher for Zaovine compared to Vlasina. Significantly lower HP index for liver and the total HP index value were observed for fish from Vlasina compared to Perućac. No significant human health risks due to the intake of examined pollutants in each reservoir were recorded; women were at higher risk compared to men. A reason for concern is a few muscle samples from Garaši, Vlasina, Perućac, and Medjuvršje in which Cd exceeded the MAC. A reservoir for water supply (Garaši) is generally considered the safest for fish consumption.

Dysbiosis of fish gut microbiota is associated with helminths parasitism rather than exposure to PAHs at environmentally relevant concentrations

Although parasite infection and pollution are common threats facing wild populations, the response of the gut microbiota to the joint impact of these stressors remains largely understudied. Here, we experimentally investigated the effects of exposure to Polycyclic Aromatic Hydrocarbons (PAHs) and infection by a common acanthocephalan intestinal parasite (Pomphorhynchus sp.) on the gut microbial flora of a freshwater fish, the European chub (Squalius cephalus). Naturally infected or uninfected individuals were exposed to PAHs at environmentally realistic concentrations over a five-week period. Characterization of the gut bacterial community through 16S rRNA gene amplicon sequencing revealed that parasitic infection was a more structuring factor of bacterial diversity and composition than PAH exposure. Specifically, chub infected by Pomphorhynchus sp. harbored significantly less evenly represented gut bacterial communities than the uninfected ones. In addition, substantial changes in sequence abundance were observed within the main bacterial phyla, including the Firmicutes, Fusobacteriota, Actinobacteriota, and Proteobacteria. Again, these compositional changes correlated with host infection with Pomphorhynchus sp., confirming its pivotal role in gut microbial assemblage. Overall, these results highlight the importance of defining the parasitic status of individuals when conducting microbial ecotoxicological analyses at the digestive tract level, as this should lead to better understanding of microbiota modulations and help to identify microbial markers specifically associated with chemicals.

Bioaccumulation of per- and polyfluoroalkyl substance in fish from an urban river: Occurrence, patterns and investigation of potential ecological drivers

Per- and polyfluoroalkyl substances (PFAS) are ubiquitous in aquatic environments and a recent shift toward emerging PFAS is calling for new data on their occurrence and fate. In particular, understanding the determinants of their bioaccumulation is fundamental for risk assessment purposes. However, very few studies have addressed the combined influence of potential ecological drivers of PFAS bioaccumulation in fish such as age, sex or trophic ecology. Thus, this work aimed to fill these knowledge gaps by performing a field study in the Seine River basin (France). Composite sediment and fish (European chub, Squalius Cephalus) samples were collected from four sites along a longitudinal transect to investigate the occurrence of 36 PFAS. Sediment molecular patterns were dominated by fluorotelomer sulfonamidoalkyl betaines (i.e. 6:2 and 8:2 FTAB, 46% of ∑PFAS on average), highlighting the non-negligible contribution of PFAS of emerging concern. C9–C14 perfluoroalkyl carboxylic acids, perfluorooctane sulfonic acid (PFOS), perfluorooctane sulfonamide (FOSA) and 10:2 fluorotelomer sulfonate (10:2 FTSA) were detected in all fish samples. Conversely, 8:2 FTAB was detected in a few fish from the furthest downstream station only, suggesting the low bioaccessibility or the biotransformation of FTABs. ∑PFAS in fish was in the range 0.22–3.8 ng g−1 wet weight (ww) and 11–140 ng g−1 ww for muscle and liver, respectively. Fish collected upstream of Paris were significantly less contaminated than those collected downstream, pointing to urban and industrial inputs. The influence of trophic ecology and biometry on the interindividual variability of PFAS burden in fish was examined through analyses of covariance (ANCOVAs), with sampling site considered as a categorical variable. While the latter was highly significant, diet was also influential; carbon sources and trophic level (i.e. estimated using C and N stable isotope ratios, respectively) equally explained the variability of PFAS levels in fish.

Accumulation of 25 elements in gills, liver, gonads, and muscle of European chub (Squalius cephalus), Cactus roach (Rutilus virgo), and pikeperch (Sander lucioperca) from Zlatar reservoir (Serbia).

Accumulation of Al, As, B, Ba, Ca, Cd, Co, Cr, Cu, Fe, Hg, K, Li, Mg, Mn, Mo, Na, Ni, P, Pb, S, Se, Si, Sr, and Zn was analyzed in gills, liver, gonads, and muscle of European chub (Squalius cephalus), Cactus roach (Rutilus virgo), and pikeperch (Sander lucioperca) from Zlatar reservoir (Serbia) using inductively coupled plasma optical emission spectrometry (ICP-OES). The highest concentrations of Cu in liver as well as Ba, Ca, Fe, Mn, Na, P, and Sr in gills were detected in all fish species, while the lowest concentrations of Cu, Fe, Mn, Na, and Zn were detected in muscle. Pikeperch had significantly lower concentrations of Ba in all tissues compared to the other species, as well as Fe, P, and Sr in muscle, K, Mg, Mn, Sr, and Zn in gills, and Fe in gonads. European chub had significantly higher concentrations of Ca, Cu, and Zn in muscle, Cu in liver, and Cr and Cu in gonads compared to Cactus roach and pikeperch. Cd concentration in one individual of Cactus roach exceeded the maximum allowed concentration. The muscle was exposed to the lowest pressure of metal pollution in all species, and European chub accumulated more metals compared to the other species. There is no significant health risk due to consumption of investigated species. A major hazard index (HI) contributor in all species was Hg. According to the target carcinogenic risk factor (TR), target hazard quotient (THQ), and HI, men are under lower health risk compared to the women. The TR and THQ for As, Cr, Cu, Fe, Mn, Ni, and Zn as well as HI values were higher for European chub compared to the other species. On the other hand, THQ for Hg was highest for pikeperch.

Fish health in the Nidda as an indicator for ecosystem integrity: a case study for Central European small streams in densely populated areas

BackgroundIn Germany and the EU, most headwaters are still far from reaching a good chemical and ecological status as it is required by the European Water Framework Directive (WFD), until 2027 the latest. Particularly, in densely populated areas, impacts from municipal and industrial wastewater discharges or diffuse agricultural emissions are still a matter of concern. This also applies to the Nidda River which is considered to be in a moderate to rather poor condition. In our study, we investigated short-term and long-term consequences of anthropogenic pollution on fish health via one monitoring with caged fish (CF) and two field sampling campaigns (FF). In the CF monitoring, rainbow trout (Oncorhynchus mykiss) were caged for seven weeks at four selected sites along the Nidda, whereas in the FF monitoring approach, feral fish, including brown trout (Salmo trutta f. fario), European chub (Leuciscus cephalus) and stone loach (Barbatula barbatula) were caught in June and September 2016.ResultsHistopathological analyses of liver and gills were conducted, accompanied by measurements of hepatic 7-ethoxyresorufin-O-deethylase (EROD) activity to assess the cytochrome P450 (CYP1A1) function, and genotoxicity via the micronucleus assay. Caged as well as field-captured fish exhibited impaired health conditions showing lesions particularly in the liver, and a presumably overwhelmed CYP1A1 system, whereas genotoxicity was not induced. The variation between sampling sites and seasons was rather low, but two trends were recognisable: (a) liver condition was poorest around spawning season and (b) tissue integrity and EROD activity were most affected downstream of industrial dischargers. Furthermore, effects were species dependent: the generally highly sensitive S. trutta f. fario proved to be impacted most, whereas L. cephalus with its pelagic lifestyle was affected less than the benthic B. barbatula, indicating a relevant contamination of sediments.ConclusionOur results confirm the impaired ecological state of the Nidda and emphasise that a sustainable improvement of aquatic ecosystem health needs to include both water quality and sediment contamination to approach the ambitious WFD goal.

Acipensor Stellatus, Rutilus (Rutilus) Caspicus, Leuciscus Cephalus Orientalis of the Fauna of the Nakhchivan Autonomous Republic Faunistic Analysis of Fishes

Summarizing the obtained literature materials and the results of our research, it was determined that 33 fish species or subspecies consisting of 6 groups, 9 chapters and 28 genera are distributed in the waters of Nakhchivan AR. Acipenser stellatus - A fairly large fish, its adult individuals in the ichthyofauna of Azerbaijan vary in body length from 105 to 225 cm and weight from 9 to 73 kg. The body stretches. Rutilus rutilus caspicus - A number of esophageal teeth, gingival teeth are sparse and rough. It is the only widespread species in Azerbaijan. The body, slightly flattened on the sides, is covered with fairly large scales. The eyes are large, the iris is red. Leuciscus cephalus orientalis - Fish is distinguished by broad and rigid forehead, cylindrical and large scales. The eyes are big and bright.

Isolation, Identification and Characterization of a Novel Megalocytivirus from Cultured Tilapia (Oreochromis spp.) from Southern California, USA.

Simple SummaryAquaculture is the world’s fastest-growing food production sector, with tilapia (Oreochromis spp.) among the most important cultured species. First reported in red seabream, Pagrus major, in 1990, an increasing number of megalocytiviruses are responsible for losses that threaten the production and economic sustainability of important cultured fish species, including tilapia. In the current study, we describe an epizootic in tilapia fingerlings from Southern California, USA and report the discovery of a novel megalocytivirus associated with the mortalities. In spring 2019, diseased four-month-old tilapia (Oreochromis spp.) from an aquaculture farm in Southern California, USA were received for diagnostic evaluation with signs of lethargy, anorexia, abnormal swimming, and low-level mortalities. At necropsy, non-specific external lesions were noted including fin erosion, cutaneous melanosis, gill pallor, and coelomic distension. Internal changes included ascites, hepatomegaly, renomegaly, splenomegaly, and multifocal yellow-white nodules in the spleen and kidney. Cultures of spleen and kidney produced bacterial colonies identified as Francisella orientalis. Homogenized samples of gill, brain, liver, spleen, and kidney inoculated onto Mozambique tilapia brain cells (OmB) developed cytopathic effects, characterized by rounding of cells and detaching from the monolayer 6–10 days post-inoculation at 25 °C. Transmission electron microscopy revealed 115.4 ± 5.8 nm icosahedral virions with dense central cores in the cytoplasm of OmB cells. A consensus PCR, targeting the DNA polymerase gene of large double-stranded DNA viruses, performed on cell culture supernatant yielded a sequence consistent with an iridovirus. Phylogenetic analyses based on the concatenated full length major capsid protein and DNA polymerase gene sequences supported the tilapia virus as a novel species within the genus Megalocytivirus, most closely related to scale drop disease virus and European chub iridovirus. An intracoelomic injection challenge in Nile tilapia (O. niloticus) fingerlings resulted in 39% mortality after 16 days. Histopathology revealed necrosis of head kidney and splenic hematopoietic tissues.

The Interannual Variability of the Fall Size of Young-of-The-Year Chub (Squalius cephalus): Influence of Phenology, Growth Patterns and Abiotic Factors

Long-term surveys confirm the rapidity of environmental and biological changes undergone by endangered species but that also concerned relatively “tolerant” species, especially common rheophilic species such as European chub (Squalius cephalus, Linnaeus 1758). As many organisms, fish are highly vulnerable during their first life stages. Body size is a determinant factor for ecosystem functioning and for fish to survive to predators or to winter conditions. While numerous studies has already demonstrated the large variability of autumnal size of fish hatched during the year, few have focused on the factors explaining these interannual variations and on the growth patterns underlying these distributions. Using otoliths of young-of-the-year (YOY), we studied how the interannual variability in fall sizes of chub might be related to varying phenology, temperature, hydrology and growth patterns. YOY were sampled in three sections of the same reach of the Rhône River with contrasted hydrological regime: an artificial deep lotic channel (the tailrace of Bollène), a bypassed section with both lotic and lentic areas (former river channel before dam construction) and a reservoir with lentic deep waters. Sampling was performed on each sector during two thermally distinct years. Temperature had an important effect on both phenology and growth rate but it was not expressed similarly among river sections. Fish hatched earlier in the warmer year. Fish sizes were positively correlated with growing degree-days, but with distinct relationships between years and sections. The growth was faster in the warmer year, and in the warmer section, but differences in growth patterns varied between sections. In the bypassed section, the difference was slight, almost not significant, even if temperatures were very different between the 2 years considered. Autumnal variations in size could be explained either by an earlier phenology or by a faster growth due to higher temperatures occurring during the final part of the growing period. Our results were in accordance with general theory’s predictions relating individual growth to temperature, but they also showed that other factors might mitigate the influence of temperature on fish early life stages.

Spawning areas and migration patterns in the early life history of Squalius cephalus (Linnaeus, 1758): Use of otolith microchemistry for conservation and sustainable management

Abstract In the context of the River Rhône restoration programme, the objective of this study was to assess the dispersal and population connectivity of the European chub, Squalius cephalus (Linnaeus, 1758) in a section of the natural, free‐flowing part of the lower River Rhône. The elemental water signatures for Sr:Ca and Ba:Ca were measured at seven stations within the river section, including its tributaries and backwaters, to determine whether they could be differentiated by microchemistry. From August to October the signatures differed among three sectors of the study reach: the Rhône; the Ardèche; and the backwaters. The elemental signatures of the otoliths of 178 young‐of‐the‐year (YOY) chub from the stations were measured to assess spawning areas and identify early migratory life histories. Analyses of otolith microchemistry identified the natal origin of 95% of the fish. Sr:Ca signatures of otoliths showed early downstream migration for 30.4% of the YOY chub; however, 70% of the fish recruited relatively close to their spawning origin suggesting a potential inshore retention of fish. The results showed (i) a non‐negligible contribution of the tributaries and backwaters in the recruitment of fish into the main channel; and (ii) the ability of chub to migrate over several kilometres during their first few months of life. This study shows that the combination of water and otolith microchemistry analyses of fish growth increases the understanding of fish life history. Moreover, the study revealed that half of the YOY fish from this river section came from the tributaries and the other half came from reproduction in the River Rhône (despite its high anthropization). These methods offer promising future applications of otolith microchemistry for river management in the context of ecological rehabilitation, especially to assess the effectiveness of measures applied in the restoration of floodplain connectivity for riverine fish population conservation.

Investigations on Endohelmint Fauna of Teleost Fishes of Aras and Murat Rivers in Turkey

In this study which has been done between April 2008 and June 2009, fishes captured from Ağrı and Erzurum were examined by endoparasite fauna. Examined fishes are as follows: Acanthobrama marmid Heckel, 1843, Alburnus akili Battalgil, 1942, Barbus plebejus Bonaparte, 1839, Barbus mursa Güldenstädt, 1773, Capoeta barroisi Lortet in Barrois, 1894, Capoeta capoeta Güldenstädt, 1773, Cyprinus carpio Linnaeus, 1758, Leuciscus cephalus Linnaeus, 1758. Consequently, a total of 908 individual parasites were detected from six parasite species; Rhabdochona denudata Dujardin, 1845 (Nematoda), Neoechinorhynchus sp. and Pomphorhynchus sp. (Acanthocephala), Bothriocephalus acheilognathi Yamaguti, 1934, and Caryophyllaeus laticeps Pallas, 1781 (Cestoda), Allocreadium isoporum Looss, 1894 (Digenea). The distribution of the infection prevalence, mean intensity, and abundance values of parasite species were determined. As a result of our study, 93 of 233 (39.91%) fish were reported with parasites.

DETERMINATION OF SOME ESSENTIAL AND NON-ESSENTIAL MINERAL ELEMENTS IN EDIBLE TISSUE IN THREE FISH SPECIES FROM GREATER ZAB RIVER, ERBIL GOVERNORATE, KURDISTAN REGION OF IRAQ

The purpose of the current study was to determine certain mineral components in edible tissue in different species of fish from Greater Zab River, Erbil Governorate- Kurdistan Region-Iraq. A total of 180 fish namely Capoeta trutta, Chondrostoma regium and Leuciscus cephalus were collected from Gali Balinda, Bn Khiveta, Galiesule, Pirsal and Bekhme between July and November 2019. After removal of eviscerated, deboned, head and fins, fish were washed with purified water and muscle samples were collected above the lateral line between the dorsal fin and the caudal fin, then dried for important and non-essential metals examination at 750 C for 48 h. Results showed that levels of K, Na, P, Ca, Cd and Hg in the edible tissue of Chondrostoma regium fish were significantly higher than in the Capoeta trutta and Luciobarbus esocinus fish, whereas the edible tissue in Capoeta trutta exhibited the highest mean values for lead, barium and arsenic. In all species, the highest concentrations of K, Na, and Mg were recorded in Gali Balinda, whereas the highest concentration of P and Ca were recorded in Pirsal during studied period. According to the results, the government should have environmental policies to improve, keep and enrich the water quality assessment in Greater Zab River

Fish from urban rivers and with high pollutant levels have shorter telomeres.

Environmental pressures, such as urbanization and exposure to pollutants may jeopardize survival of free-living animals. Yet, much remains to be known about physiological and ecological responses to currently-released pollutants, especially in wild vertebrate ectotherms. We tested the effect of urbanization and pollution (phthalates, organochlorine and pyrethroid pesticides, polychlorobiphenyls, polybromodiphenylethers, polycyclic aromatic hydrocarbons, and some of their metabolites) on telomere length, a suggested biomarker of life expectancy, in the European chub, Squalius cephalus, from urban and agricultural rivers of the Marne hydrographic network, France. We showed that telomere length was reduced in chub from urban rivers. Moreover, among the wide range of anthropogenic contaminants investigated, high levels of phthalate metabolites in liver were associated with shorter telomeres. This study suggests that urbanization and chemical pollution may compromise survival of wild fish, by accelerating telomere attrition.

Can top-down effects of cypriniform fish be used to mitigate eutrophication effects in medium-sized European rivers?

Eutrophication seriously threatens the ecological quality and biodiversity of running waters. In nutrient-enriched streams and shallow rivers, eutrophication leads to excessive periphyton growth and, in turn, biological clogging, oxygen depletion in the hyporheic zone and finally a reduction in the hyporheic habitat quality. Top-down control of the food-web by manipulating fish stocks, similar to the biomanipulation successfully applied in lakes, offers a promising approach to mitigating the effects of eutrophication in shallow rivers, especially those in which major reductions in nutrient input are not feasible. We conducted a reach-scale experiment over 4 years in a medium-sized eutrophic river to assess whether the top-down effects of two important large European cypriniform fish species, herbivorous common nase (Chondrostoma nasus) and omnivorous European chub (Squalius cephalus), would mitigate the effects of eutrophication. The enhancement of fish stocks was expected to reduce biological clogging, via the top-down control of periphyton by benthic grazing and enhanced bioturbation, thus increasing oxygen availability in the hyporheic zone as well as water exchange between the surface water and the hyporheic zone. As expected, enhancing the stocks of nase and chub increased both oxygen availability and vertical exchange flux of water in the upper layer of the hyporheic zone. However, periphyton biomass (chlorophyll a) was significantly reduced only in deeper pool habitat. Thus, while experimental biomanipulation in a shallow river significantly mitigated the effects of eutrophication in the hyporheic zone, top-down effects on periphyton biomass were rather small. Overall, to our knowledge, our results provide first evidence that the biomanipulation achieved by enhancing herbivorous and omnivorous fish stocks has the potential to mitigate the effects of eutrophication in medium-sized European rivers.

Acanthocephalan parasites collected from Austrian fishes: molecular barcoding and pathological observations.

Acanthocephalan parasites were collected from the intestinal tracts of 137 predominantly wild fish (1 barbel Barbus barbus, 3 European chub Squalius cephalus, 13 rainbow trout Oncorhynchus mykiss and 120 brown trout Salmo trutta) from 12 localities. The condition factor, intensity of acanthocephalan infection and pathological lesions, if applicable, were documented. Routine bacteriology and virology were performed, and the brown trout were additionally tested for the presence of the myxozoan parasite Tetracapsolioides bryosalmonae by PCR. In total, 113 acanthocephalans were barcoded by sequencing a section of the mitochondrial cytochrome oxidase subunit I (COI) gene. Barcoding of the acanthocephalan tissues resulted in 77 sequences, of which 56 were assigned to Echinorhynchus truttae (3 genotypes), 11 to Pomphorhynchus tereticollis (9 genotypes), 9 to Acanthocephalus sp. (5 genotypes) and 1 to Neoechinorhynchida. Most of these genotypes were detected for the first time. Statistically, the acanthocephalan infection did not have an impact on the condition factor of the brown trout. Infection with P. tereticollis caused more severe pathological changes in the digestive tract than E. truttae. The present study provides new data regarding the distribution of acanthocephalan species in Austria and their impact on individual fish. In addition, new barcoding data from acanthocephalan parasites are presented, and the occurrence of P. tereticollis in European chub in Austria and in brown and rainbow trout in general was confirmed for the first time.

Cypriniform fish in running waters reduce hyporheic oxygen depletion in a eutrophic river

Abstract The hyporheic zone is an important habitat for benthic invertebrates and early‐developmental stages of gravel spawning fish. However, the eutrophication of running waters and, in turn, the excessive periphyton biomass leads to its biological clogging. The result of these processes is oxygen depletion and a reduction in the habitat quality of the hyporheic zone. This study assessed whether top‐down effects of two important European river fish species, the large herbivorous cypriniform common nase (Chondrostoma nasus, L.) and the large omnivorous cypriniform European chub (Squalius cephalus, L.), can reduce eutrophication effects in the hyporheic zone. A 4‐week mesocosm‐based field experiment in a eutrophic river was conducted using cage enclosures stocked or not with either nase or chub. The top‐down control of periphyton was expected to reduce biological clogging and thereby increase oxygen availability in the hyporheic zone. Accordingly, we hypothesised that in enclosures stocked with either fish the concentrations of dissolved oxygen in the hyporheic zone would be higher and the periphyton biomass would be lower than in enclosures without fish stocking. Hyporheic oxygen concentrations were significantly higher in enclosures stocked with either nase or chub than in enclosures without fish stocking. However, periphyton ash‐free dry mass was significantly reduced only in enclosures stocked with nase, not in those stocked with chub. Thus, the positive effects of nase and chub on hyporheic oxygen availability were caused by different mechanisms. Our results demonstrate that nase and chub can reduce eutrophication effects in the hyporheic zone of running waters. Hence, protecting and enhancing stocks of herbivorous and omnivorous fish will contribute to restoring the hyporheic zone in efforts to preserve biodiversity in eutrophic rivers.