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Invasive fish species impact aquatic ecosystems and modify native communities, often leading to a decline in local species. These ecological impacts include the transmission of pathogens, predation, competition as well as hybridization. Two invasive fish species, the common bleak Alburnus alburnus and the topmouth gudgeon Pseudorabora parva, have both been recently found co-occurring in several regions of southern Europe, such as the Italian Arno River. Nonetheless, the trophic relationships among invasive fish species, especially cyprinids, remain poorly understood, and no studies have reported the trophic interaction between these two species. This study compared length-weight relationship and used stomach content and stable isotope analysis of two co-occurring populations in the Arno River to characterize the growth and overlap of potential trophic niches. It also found similar allometric growth in both species, a wider generalist trophic niche for P. parva and a more specialized niche for A. alburnus. A considerable niche overlap was found, suggesting that feeding competition can occur if resources were to be limited. Moreover, the niche of P. parva was more likely to overlap with that of A. alburnus than vice versa, suggesting that P. parva can be considered as a potential over competitor. Nonetheless, the authors found in the overlapping populations no evidence of realized competition, probably avoided through a combination of fine-scale mechanisms. They also highlighted that these two invasive species can co-exist and share resources, at least in an open ecosystem like a river, thus potentially doubling up their trophic impact on local communities.

ADONIS:CE has been used as a base to create a support-system management decision-making model for Alburnus alburnus (Linnaeus, 1758) and Alburnoides bipunctatus (Bloch, 1782) species. Investigation of the habitat necessities and the identification of the necessary elements for a good status of conservation of these two fish species populations has revealed the pressures and threats to these congener species, for which specific management activities have been finally recommended.

Background. In this study, we present the results concerning the growth, reproduction, and trophic activities of bleak, Alburnus alburnus (Linnaeus, 1758), a cyprinid fish recently introduced to Algeria. We need to show that this species is adapted to local conditions. We have also characterized the biological activity of the bleak and the impact of environmental parameters on this activity. Materials and methods. The fish sampling was carried out monthly from May 2008 through February 2012 in Keddara Dam Lake, from a single sampling station located in the proximity of the dam. We studied the biometric parameters of the fish, their length–weight relation, growth parameters, the reproductive and trophic activities, as well as the physical and chemical properties of the water. The data collected were processed and interpreted using selected biological indices. The climatic data were obtained from the Algerian National Office of Meteorology. The statistical analysis was performed using the R program. Results. The length–weight relation of bleak represented positive allometry. The females grew less rapidly than males between 2–3 years of age. Beyond this age, females grew faster. The condition factor of females and males indicated that environmental conditions were unstable and varied between poor and good. The sex ratio was in favour of females. The reproduction activity was relatively spread over time. During the year there were many phases of sexual maturation and several spawning periods (3–4), which started from the end of January and lasted until the end of July. The last late spawning was between November and December. The sexual rest period was observed between August and September. The hepatosomatic index, in both sexes, showed no great differences. Also, the viscerosomatic index was stable. However, the repletion index was steadily increasing throughout the year. The RDA analysis analysis allows characterizing the biological activity of the bleak and the impact of environmental parameters. Conclusion. We have characterized the biological and ecological variability of Alburnus alburnus in its new biotope and the relation of this species to the environmental parameters. This study brings new evidence for the adaptive potential of exotic species introduced in North Africa.

This article belongs to the Special Issue Ecology and Conservation of Freshwater Fishes Biodiversity., The bleak Alburnus alburnus is native to most of Europe. This cyprinid fish is a successful invader in the Iberian Peninsula. No studies exist on its foraging strategies on a large scale for this ecoregion. The aim of the present study was to compare dietary traits of invasive bleak among the main Iberian rivers and a ‘reference’ native bleak population from France. Bleak were sampled during May–June 2019 from the Iberian Rivers Ebro, Tagus, Guadiana, Segura and Guadalquivir and the River Saône (France). Diptera larvae and zooplankton were common food categories in the River Saône. Insect nymphs were more important in the River Ebro. The intake of plant material was higher in the River Tagus. Flying insects were more consumed in the River Guadiana. Nektonic insects were important in the River Guadalquivir. Detritus was a frequent food category for all populations, in terms of occurrence and mass. Dietary parameters followed a unimodal response in relation to the latitudinal gradient, with the maximum values for the Tagus and Guadiana populations. Overall, results suggest that this wide interpopulation variability will contribute to the species’ successful establishment throughout Mediterranean Europe, which poses a serious risk to its highly valuable native fish fauna, This research was partly supported by the Spanish Ministry of Education (FPU 13/03291), the Spanish Ministry of Economy and Competitiveness (projects CGL2015-69311-REDT and CGL2016-80820-R) and the Government of Catalonia (ref. 2014 SGR 484).

Length-weight relationships (LWRs) and length-length relationships (LLRs) were determined for six fish species: Alburnus alburnus, Blicca bjoerkna, Gymnocephalus cernua, Perca fluviatilis, Rutilus rutilus and Sander lucioperca caught using a Nordic multi-mesh gill net in Lake Kirkkojärvi in Southwestern Finland in August 2015. The measurements were done using a photographic method and the dataset is available on the Comprehensive R Archive Network (CRAN). The dataset was done with a scientific catch, which showed lower limits on specimen size than the ones from fisheries. The LWRs were calculated for the total length (TL) and found to be consistent with models from Finland. The length measurements were taken to the nearest 0.01 cm, which also allowed for juveniles to be represented in the model. The goodness of fit of the models is high, with the coefficients of determination above 95%. This study is the first one to estimate LWRs of fish species for this hypereutrophic lake, and is useful for fishery managers and biologists.

Historic fisheries data collected from locations across the UK over several years were compared with predicted estrogen exposure derived from the resident human population. This estrogen exposure could be viewed as a proxy for general sewage (wastewater) exposure. With the assistance of the Environment Agency in the UK, fisheries abundance data for Rutilis rutilis (roach), Alburnus alburnus (bleak), Leuciscus leuciscus (dace) and Perca fluviatilis (perch) from 38 separate sites collected over 7 to 17 year periods were retrieved. From these data the average density (fish/m2/year) were compared against average and peak predicted estrogen (wastewater) exposure for these sites. Estrogen concentrations were predicted using the LF2000-WQX model. No correlation between estrogen/wastewater exposure and fish density could be found for any of the species. Year on year temporal changes in roach population abundance at 3 sites on the middle River Thames and 4 sites on the Great Ouse were compared against estrogen exposure over the preceding year. In this case the estrogen prediction was calculated based on the upstream human population providing the estrogen load and the daily flow value allowing concentration to be estimated over time. At none of the sites on these rivers were temporal declines in abundance associated with preceding estrogen (effluent) exposure. The results indicate that, over the past decade, wastewater and estrogen exposure has not led to a catastrophic decline in these four species of cyprinid fish.

The bleak Alburnus alburnus (L., 1758) is a limnophilic fish native to most of Europe. This cyprinid species is a successful invader in the Iberian Peninsula, where it threatens the highly endemic fish fauna. However, studies on bleak autoecology are scarce in this region, with few data on foraging strategies. The aim of this work was to compare the dietary traits of bleak populations between contrasting habitats in Iberian fresh waters. For this purpose, bleak were seasonally collected from the small River Gevora and the Sierra Brava Reservoir (Guadiana River Basin, southwestern Spain). As percentages of occurrence and ingested mass, plant material and planktonic Crustacea were the most important food categories in the river and the reservoir, respectively. The intake of pelagic prey was higher in the reservoir, especially during summer. Benthic prey, plant material and detritus were more consumed in the river, especially benthos and detritus during spring, whereas plant intake decreased during this season. Shannon index, as a measure of trophic diversity, was higher in the reservoir, except for spring. Overall results suggest that this wide trophic plasticity will facilitate the bleak invasion process throughout Mediterranean Europe, which poses a serious risk to its highly valuable native fish fauna.

The Iberian Peninsula has been subjected to numerous fish introductions and the colonization of new areas by non-native species is constantly reported. However, there is a lack of knowledge about many aspects of the bio-ecology of these species and their invasive success within the environmental context of Mediterranean temporary rivers. This study aimed to address the following questions: (i) what are the main regional and local environmental drivers influencing fish assemblages and differentiating native from non-native species, particularly A. alburnus?, (ii) what are the environmental and anthropogenic disturbance factors responsible for the occurrence and abundance of A. alburnus?, (iii) is there a pattern in the spatiotemporal distribution of A. alburnus size classes, along the tributaries of reservoirs where the species occurs? Data on fish species, environmental variables, and anthropogenic disturbance were collected in 77 sites of the Guadiana and Sado river basins in the south of Portugal. Additionally, a seasonal sampling was performed along an upstream-downstream gradient of several tributaries from three reservoirs in these river basins. A multivariate analysis and a multi-model approach were used in data analyses. Native and non-native fish assemblages showed different environmental drivers and responses to anthropogenic disturbance levels, though A. alburnus has revealed similarities with native species. The occurrence of A. alburnus was mainly determined by hydrological and morphological disturbances driven by anthropogenic activities. Furthermore, this species apparently performed seasonal movements along the tributaries of several reservoirs, profiting from these lentic habitats as a stepping-stone for further invasions. This study highlighted the wide ecological plasticity of A. alburnus, as it benefits from the anthropogenic hydrological disturbance (induced by reservoirs), and is also able to cope with the natural hydrological disturbance (resulting from the intermittency of these streams), to guarantee and enhance its invasive success in Mediterranean intermittent streams. It also gives a sound contribution to understand the spread of A. alburnus in these vulnerable freshwater ecosystems, and to delineate management measures, namely by identifying critical points in the river network along with prioritizing river restoration measures that benefit native species.

Besides food quality control of fish or cephalopods, the novel mass spectrometry (MS) approaches could be effective and beneficial methods for the investigation of biodiversity in ecological research. Our aims were to verify the applicability of MALDI-TOF MS in the rapid identification of closely related species, and to further develop it for sex determination in phenotypically similar fish focusing on the low mass range. For MALDI-TOF MS spectra analysis, ClinProTools software was applied, but our observed classification was also confirmed by Self Organizing Map. For verifying the wide applicability of the method, brains from invertebrate and vertebrate species were used in order to detect the species related markers from two mayflies and eight fish as well as sex-related markers within bleak. Seven Ephemera larvae and sixty-one fish species related markers were observed and nineteen sex-related markers were identified in bleak. Similar patterns were observed between the individuals within one species. In contrast, there were markedly diverse patterns between the different species and sexes visualized by SOMs. Two different Ephemera species and male or female fish were identified with 100% accuracy. The various fish species were classified into 8 species with a high level of accuracy (96.2%). Based on MS data, dendrogram was generated from different fish species by using ClinProTools software. This MS-based dendrogram shows relatively high correspondence with the phylogenetic relationships of both the studied species and orders. In summary, MALDI-TOF MS provides a cheap, reliable, sensitive and fast identification tool for researchers in the case of closely related species using mass spectra acquired in a low mass range to define specific molecular profiles. Moreover, we presented evidence for the first time for determination of sex within one fish species by using this method. We conclude that it is a powerful tool that can revolutionize ecological and environmental research.

Desert rivers are highly dynamic systems in which dry periods, frequently involving the cessation of superficial flow, alternate with violent flash floods. In spite of their territorial importance and high functional and biological diversity, desert rivers have received little attention in the scientific literature, especially in Northern Africa. This study investigated the distribution of non-native fish, their relationship with river damming and their potential impacts on native biodiversity in the main river basins draining arid areas of Morocco (Oued Draa, Oued Ziz and Oued Ghir), based on field sampling covering 84 stream reaches. Thirteen fish species were recorded, eight of which are non-native. Two species (stone moroko, Pseudorasbora parva, and bleak, Alburnus alburnus) had not been previously recorded in Morocco, while the native sandsmelt (Atherina boyeri) had not been cited as an invader. Pumpkinseed (Lepomis gibbosus) was the most widely distributed non-native fish. Non-native fish species were associated with reservoirs, colonizing the regulated downstream reaches. In contrast, unregulated upstream reaches tended to be free of non-natives. The low abundance of native fish in reservoirs seems to be caused by the impacts of introduced fish species. Management options for environmental flow are limited, owing to reduced water availability. Non-native fish management should thus focus on limiting the spread of species already introduced and avoiding new introductions, especially into reservoirs. Copyright © 2014 John Wiley & Sons, Ltd.

The aim of the study was to determine the degree of overlap in the feeding niches of early developmental stages of roach, Rutilus rutilus (L.), perch, Perca fluviatilis L., bleak, Alburnus alburnus (L.) and sunbleak, Leucaspius delineatus (Heckel). The hypotheses were that (i) larvae of different fish species of similar body sizes feed on similar food, and that (ii) smaller fish compete with larger ones for similar prey. The results of the analysis was to answer the question of whether the diet overlap of juvenile fish stages decreases with ontogenetic development. The study was conducted for two years (2001-2002) in two shallow, polymictic, eutrophic lakes. The diets of early developmental stages of fish species of similar body sizes differed. The few instances of diet overlap resulted from the abundance of food resources in the environment. However, fish of smaller body sizes exploited the same food resources as did individuals of the same species that belonged to different cohorts.

White muscle has been traditionally used in determining δ 13C and δ 15N signatures in fish but ethics and the current conservation status of many species mean the application of non-lethal sampling procedures is mandatory. In this study we test whether fins and scales can be used as non-lethal alternatives of muscle tissue for stable isotope analysis by comparing their δ 13C and δ 15N signatures, in two native (Barbus haasi, Squalius laietanus) and three introduced fish species (Rutilus rutilus, Lepomis gibbosus and Alburnus alburnus), collected in rivers from north-eastern Spain. Our results showed fins and scales were generally enriched in 13C and depleted in 15 N compared to muscle, and that both tissues were generally a moderate predictor of the isotopic composition of muscle for most species with the exception of Ebro chub (R 2 = 0.59–0.97). This study highlights the importance of determining the isotopic relationship between lethal and non-lethally sampled tissues before making straightforward equivalences, and also pinpoints the need for a more comprehensive understanding of how isotopic discrimination occurs in fins, scales and muscle tissues.

Summary The western part of the Bryansk region (Russia) was seriously contaminated with radioactive isotopes by the Chernobyl disaster in 1986. Contamination level of this area is similar to contaminated regions in Ukraine and Belarus. We studied the fluctuating asymmetry of two cyprinid species, roach Rutilus rutilus and bleak Alburnus alburnus, to assess the effect of radioactive contamination on developmental stability. Fluctuating asymmetry represents random deviations from perfect, usually bilateral symmetry, and is often used to assess developmental stability. Fish were collected in summer 1992 from the Desna and Iput rivers of the Bryansk region with similar hydrological characteristics but with differing levels of radioactive contamination. Contamination in the Desna River exceeded the background level of non-contaminated areas, but was considerably lower than in the Iput River. Roach were 3–5 years old and bleak 1–2 years old. In total, 78 specimens were analyzed, with 13 roach and 26 bleak from each location. We examined 39 meristic and 18 morphometric characters in cranial bones of roach and 23 meristic and 13 morphometric characters in bleak. No significant differences in meristic or morphometric characters were found between roach from the contaminated and reference locations. In bleak, we found significantly higher fluctuating asymmetry in meristic (P test, P

The bleak Alburnus alburnus (L.) is a cyprinid native to most of Europe, mainly inhabiting lentic environments. This fish species is a successful invader in the Iberian Peninsula, where it was first introduced to reservoirs as forage fish during the 1990s. Bleaks threaten the highly endemic Iberian fish fauna by means of trophic competition and hybridization. Yet, little is known about the environmental biology of bleaks in the Iberian Peninsula, particularly far from impounded waters. Thus, the aim of this work was to compare seasonal and gender variation of size structure, body condition and reproductive investment of bleaks between different habitats. Only sexually mature bleaks were seasonally collected and examined from the River Gevora and the Sierra Brava Reservoir (southwestern Spain) to assess more in-depth the adaptive capacity at the population level and the subsequent invasiveness. Bleak was an abundant species in the fish assemblages of both habitat types (i.e. river and reservoir). The proportion of smaller mature bleaks was lower in the river than the reservoir during spring and the opposite pattern was observed during winter. Both male and females were larger in the river during the breeding season in the study areas (i.e. spring), as well as with higher body condition and reproductive investment. These findings suggest that bleaks enhance their reproduction rate in the river to compensate for higher mortality in this habitat, where environmental conditions may be harsher due to the winter floods and summer droughts typical of Mediterranean water courses. Overall results highlight the high degree of plasticity in population traits of the bleak in the Iberian Peninsula, which will surely aid its ability to adapt to a wide variety of Mediterranean ecosystems, including lentic and lotic environments. Consequently, this invasive fish may pose a serious risk for the highly valuable fauna of Mediterranean Europe.

The effect of diel period and littoral habitats on the distribution of age-0 fish was tested in a deep-valley reservoir using boat-modified point abundance sampling by electrofishing (PASE). Day and night samplings unveiled differences in abundance of age-0 fish while recognizing most of the commonly present age-0 fish species in the littoral zone. Night survey provided better information about the abundance of age-0 fish since most species appeared in higher numbers at night. Alternatively, night sampling underestimated bleak (Alburnus alburnus) and gudgeon (Gobio gobio), which were predominantly found in the littoral zone in the daytime. The structure of the age-0 fish assemblage was determined primarily by the characteristics of the littoral habitats, i.e. slope steepness and structure, and three different patterns of habitat use were detected among the fish species. To obtain the most comprehensive assessment of a littoral age-0 fish assemblage and to register all species-specific patterns of habitat use, it is necessary that all littoral habitats in the reservoir are sampled during both day and night periods. The boat-modified PASE could be also used as a standard monitoring tool for routine age-0 fish sampling under difficult conditions of steep-sloped shorelines in large inland waterbodies.

[EN] Random Forests (RFs) and Gradient Boosting Machines (GBMs) are popular approaches for habitat suitability modelling in environmental flow assessment. However, both present some limitations theoretically solved by alternative tree-based ensemble techniques (e.g. conditional RFs or oblique RFs). Among them, eXtreme Gradient Boosting machines (XGBoost) has proven to be another promising technique that mixes subroutines developed for RFs and GBMs. To inspect the capabilities of these alternative techniques, RFs and GBMs were compared with: conditional RFs, oblique RFs and XGBoost by modelling, at the micro-scale, the habitat suitability for the invasive bleak (Alburnus alburnus L.) and pumpkinseed (Lepomis gibbosus L). XGBoost outperformed the other approaches, particularly conditional and oblique RFs, although there were no statistical differences with standard RFs and GBMs. The partial dependence plots highlighted the lacustrine origins of pumpkinseed and the preference for lentic habitats of bleak. However, the latter depicted a larger tolerance for rapid microhabitats found in run-type river segments, which is likely to hinder the management of flow regimes to control its invasion. The difference in the computational burden and, especially, the characteristics of datasets on microhabitat use (low data prevalence and high overlapping between categories) led us to conclude that, in the short term, XGBoost is not destined to replace properly optimised RFs and GBMs in the process of habitat suitability modelling at the micro-scale., This project had the support of Fundacion Biodiversidad, of Spanish Ministry for Ecological Transition. We want to thank the volunteering students of the Universitat Politecnica de Valencia, Marina de Miguel, Carlos A. Puig-Mengual, Cristina Barea, Rares Hugianu, and Pau Rodriguez. R. Munoz-Mas benefitted from a postdoctoral Juan de la Cierva fellowship from the Spanish Ministry of Science, Innovation and Universities (ref. FJCI-2016-30829). This research was supported by the Government of Catalonia (ref. 2017 SGR 548).

The aim of this study was to find the location of a breakpoint in the weight–length relationship using a linearized biexponential model (LinBiExp). The analysis was performed using weight and length measurements of bleak (Alburnus alburnus) individuals captured in freshwaters of the Province of Ferrara (Italy). The LinBiExp function identified the breakpoint coordinates in the data set. The level of uncertainty in the breakpoint coordinates was analysed using bootstrap regression. Bilinearity was verified by comparing slopes and intercepts (ANCOVA) of the two linear sections. The study confirmed that LinBiExp can be a valuable tool for detecting the coordinates of a breakpoint in weight–length data.

Piscivory in cyprinids (Cyprinidae) is extremely rare. Specifically, common bream (Abramis brama) and common carp (Cyprinus carpio) are zooplanktivorous fish in deep lentic waters. Nevertheless, we observed predation by these two cyprinids under natural conditions in the Vír Reservoir, Czech Republic. We conducted diet analysis for cyprinids caught by trawling and gillnets and the large amount of young-of-the-year (YOY) perch (Perca fluviatilis), with sizes of 37-52 mm standard length, were found in their digestive tracts. In 2010, a large amount of YOY perch caused a significant decrease in Daphnia spp. size and abundance in the reservoir. Hence, a food deficit was induced for the cyprinids, apparent also from the poor nutritional condition of common bream which was much worse than the condition of those in similar reservoirs. Common carp and common bream shifted to forced piscivory, and they utilized the YOY perch as an alternative food source. In contrast, smaller species, such as roach (Rutilus rutilus) and bleak (Alburnus alburnus), widely utilized planktonic cyanobacteria. In the following year, YOY perch occurred in significantly lower numbers and conversely, Daphnia spp. size and abundance were significantly higher. The forced piscivory was not observed. Our results indicate a switch to forced piscivory by cyprinids, which was caused by a shortage of their natural food source. Moreover, this phenomenon presents an effective mechanism for reduction in the numbers of YOY perch, ensuring the stability of the ecosystem.

The impacts of invasive species are recognised as a major threat to global freshwater biodiversity. The risk of invasion (probability of presence) of two avowed invasive species, the northern pike (Esox Lucius, L.) and bleak (Alburnus alburnus, L.), was evaluated in the upper part of the Cabriel River (eastern Iberian Peninsula). Habitat suitability models for these invasive species were developed with Support Vector Machines (SVMs), which were trained with data collected downstream the Contreras dam (the last barrier impeding the invasion of the upper river segment). Although SVMs gained visibility in habitat suitability modelling, they cannot be considered widespread in ecology. Thus, with this technique, there is certain controversy about the necessity of performing variable selection procedures. In this study, the parameters tuning and the variable selection for the SVMs was simultaneously performed with a genetic algorithm and, contradicting previous studies in freshwater ecology, the variable selection proved necessary to achieve almost perfect accuracy. Further, the development of partial dependence plots allowed unveiling the relationship between the selected input variables and the probability of presence. Results revealed the preference of northern pike for large and wide mesohabitats with vegetated shores and abundant prey whereas bleak preferred deep and slightly fast flow mesohabitats with fine substrate. Both species proved able to colonize the upper part of the Cabriel River but the habitat suitability for bleak indicated a slightly higher risk of invasion. Altogether may threaten the endemic species that actually inhabit that stretch, especially the Jucar nase (Parachondrostoma arrigonis; Steindachner), which is one of the most critically endangered Iberian freshwater fish species. (C) 2016 Elsevier B.V. All rights reserved., The study has been partially funded by the IMPADAPT project (CGL2013-48424-C2-1-R) with Spanish MINECO (Ministerio de Economia y Competitividad) and by the Confederacion Hidrografica del Jucar (Spanish Ministry of Agriculture, Food and Environment). We also want to thank all the colleagues who worked in the field data collection, especially Rui M. S. Costa and Aina Hernandez. Finally, we are especially grateful to Esther Lopez Fernandez who kindly and selflessly posed for the graphical abstract.

Hybrids of invasive bleak Alburnus alburnus and native endemic calandino Squalius alburnoides complex and Southern Iberian chub Squalius pyrenaicus were found in the River Jarama (Tagus River basin, central Spain). Morphological analyses show that hybrids are intermediate in shape between the parent species. Molecular mitochondrial and nuclear analyses evidence that hybridization was different in terms of the direction of gene introgression, with hybrids ♀ A. alburnus × ♂ S. pyrenaicus and ♀ S. alburnoides complex × ♂ A. alburnus. As far as we know, this is the first evidence of interspecific hybridization between a fish hybrid complex and an invasive exotic fish. The hybridization occurred at least during 3 years in a short time period after the arrival of exotic bleak. The spread of bleak in the Iberian Peninsula can be a serious threat for the survival of endemic Squalius species, as well as other close Leuciscinae such as the endangered jarabugo Anaecypris hispanica.

The composition of the fish community is studied in different lakes of the temperate climatic zone in Western Siberia. The patterns of the region’s occupation by different species in the aspect of geographical zoning are revealed. Only 7 of 19 species live within the limits of the whole region—pike Esox lucius, roach Rutilus rutilus, ide Leuciscus idus, lake minnow Phoxinus percnurus, tench Tinca tinca, crucian carp Carassius carassius, and perch Perca fluviatilis. The most stable species composition of fish is in the forest-swamp zone, where the population is formed by representatives of the aboriginal fauna. In lakes of the forest-steppe and steppe zones, six alien species, namely, sunbleak Leucaspius delineatus, bleak Alburnus alburnus, bream Abramis brama, Chinese goldfish Carassius auratus gibelio, wild carp Cyprinus carpio, and zander Sander lucioperca, have naturalized as a result of introduction. The establishment of Amur sleeper Perccottus glenii and Nikolskyi loach Misgurnus nikolskyi in water bodies of the forest-steppe zone occurs by self-spreading. At present, the share of alien species within the forest-steppe and steppe zones is 47 and 43% of fish species richness, respectively. The spatial distribution of alien species is directed from east to west within the forest-steppe zone. This is evidenced by the composition of self-spreading species whose natural range is the territory of the Far East.

Diel changes in littoral fish assemblage were studied in four reservoirs in the Czech Republic (CentralEurope). The sampling was performed by beach seining in an unstructured littoral zone. Perch, Perca fluviatilis L.,roach, Rutilus rutilus (L.), bream, Abramis brama (L.), carp, Cyprinus carpio L., ruffe, Gymnocephalus cernua (L.),pikeperch, Sander lucioperca (L.), eel, Anguilla anguilla (L.) and A. brama · R. rutilus hybrids exhibited higherdensities at night. Only bleak, Alburnus alburnus (L.) exhibited higher densities during the day. The number ofspecies was higher in night hauls, and mean body size of roach and bleak was also higher at night. Diel changes infish densities resulted in the change in species composition between day and night. The study has implication forthe sampling design to assess littoral fish assemblages using beach seine netting and recommends night samplingfor a representative assessment or sampling during both diel periods for a robust assessment. KEYWORDS

Flora and fauna have both evolved under a natural cycle of light and dark. But especially in urban areas, the night is now increasingly disturbed by artificial light. Many traits and behaviours in fish are triggered by a circadian clock, for example hatching and swim bladder inflation, which predominantly take place at dusk or night. As lighting becomes brighter and extends farther into rural areas, the distinction between day and night becomes increasingly blurred. Therefore, the loss of diurnal trigger by artificial light at night was hypothesized having deleterious effects on these traits and impact fish reproduction. To assess these effects, eggs of four native freshwater fishes, Eurasian perch Perca fluviatilis, roach Rutilus rutilus, bleak Alburnus alburnus and chub Leuciscus cephalus, were incubated under two different light conditions: a photoperiod of 14 h light:10 h darkness (LD) and continuous illumination (LL). The time to hatch and swim bladder inflation was recorded. The species showed inconsistent reactions to the light treatments. In roach and bleak, the time to 50% hatch was longer in LL, whereas continuous lighting had an accelerating effect in chub. Incubation in LL elongated the hatching period in perch and roach and, in perch, the onset of darkness seemed to trigger hatching. The swim bladder inflation was significantly promoted by continuous light in chub and bleak but was not affected in roach. In conclusion, nocturnal artificial illumination could have an effect on hatching and initial swim bladder filling by masking the day–night-change and thereby diminish the trigger effect. However, the reactions were species specific and the increase in variation indicated a lack of diurnal triggering, whilst a general deleterious effect of artificial light at night has not been identified on early life stages.

Fright bias can cause misleading results when sampling age-0 fish in beach habitats. In this study, different sampling methods were tested to reduce fright bias. Experiments using video recordings demonstrated that efficiency was 13% for extension pole electrofishing (EPE), 47% for thrown anode electrofishing (TAE), and 100% for pre-positioned anode electrofishing (PAnE). We propose a modified PAnE design for sampling age-0 fish that would not be excessively time consuming. The modified PAnE sampling design was then tested against EPE, TAE, and fine-mesh seine netting (SN). We found that PAnE sampled significantly more species and individuals than EPE and TAE. Assemblage structure sampled by PAnE differed significantly from that sampled by EPE, TAE, and SN; the difference was more substantial relative to SN than to EPE or TAE. Assemblages sampled by EPE and TAE had a lower representation of common bleak Alburnus alburnus, white-fin gudgeons Gobio albipinnatus, common dace [also known as Eurasion ...

In the course of planned or accidental fish intro� duction, rapid dispersal and range expansion are char� acteristic primarily of shortcycle species, i.e., small, early maturing fishes with partial spawning. A special place in the problem of population outbreaks and invasions belongs to the role of invasive species in the trophic structure of new biocenoses and also their role as carriers of some symbionts and parasites (Dge� baudze, 2002). The most prevalent invasive fish species in water bodies of the southern Transural region are the Amur sleeper ( Percottus glehni Dybowski, 1877), which appeared in waters of the region due to negligence of aquarists (Dubchak and Magazov, 2004) and widely dispersed in the 1980s, and the sunbleak (Leucaspius delineatus Heckel, 1843), which was brought in as eggs together with common carp spawners in the 1960 and has also dispersed widely since then (Korlyakov, 2008). The European smelt (Osmerus eperlanus Linnaeus, 1758), introduced into Bol'shoi Kisegach Lake in the 1930s, has successfully acclimated in this deep, cold� water biotope (Korlyakov and Kolenova, 2005). In the upper Tobol River basin, some river biotopes are pop� ulated by the common bleak (Alburnus alburnus Lin� naeus, 1758), which was brought in due to fishstock� ing activities in the 1970s (Andreyashkin and Dobrin� skaya, 1988; Korlyakov, 2008). These four species, which naturally reproduce in the region, represent dif� ferent faunal complexes according to Nikol'skii's (1953) classification: the Amur sleeper came from the Amur River basin; the natural range of the common bleak and sunbleak is in the Volga basin; and the Euro� pean smelt, which lives in rivers of northern Europe, represents the arctic faunal complex.

Bleak ovaries during the period preceding the reproduction and during reproduction in Lake Kortowskie were studied as concerns reproductive diversity applying standard histological methods. Among 90 females, 88 represented batch spawning while 2 females the total spawning. Presence of female total spawners suggests that sexual maturity can occur in case of the crossbreeds of bleak with one of the total spawner species crossing with bleak. NIEJEDNORODNOŚC W ROZWOJU JAJNIKOW UKLEI, ALBURNUS ALBURNUS (L.) W JEZIORZE KORTOWSKIM W POŁNOCNO-WSCHODNIEJ POLSCE Wieslawa Kopiejewska1, Jacek Kozlowski2 1Katedra Zoologii 2Katedra Biologii i Hodowli Ryb Uniwersytet Warminsko-Mazurski w Olsztynie Slowa kluczowe: Alburnus alburnus, rozwoj jajnikow, niejednorodnośc.

Summary A sample of 198 asp (Aspius aspius) was collected over a 28.5 km long section of the Danube River, upstream and downstream from the mouth of the Sava River, in order to provide information on population structure, diet, growth, and condition of this species. Total body lengths of sampled fish were 90–405 mm, and body weights 5–567 g. The sample was predominantly sub-adult fish aged 0+ to 4+ years. Sexually immature asp prevailed over the sexually mature asp. The sex ratio (1.4 : 1) was biased toward males. Male asps in the Danube become sexually mature only in their fifth year of life, and the females even later, as no sexually mature females were caught. The diet spectrum consists exclusively of fishes; of seven determined prey species, most important are bleak Alburnus alburnus, roach Rutilus rutilus, and goldfish Carassius auratus. Highest value of the seasonal vacuity index is in November (Iv = 94.1), and the smallest in July (Iv = 35.6). Trophic niche breadth is largest in May (H = 1.40), and smallest in November (H = 0.00). The largest average number of prey items is found in age class 4+ (2.33), the smallest in age class 0+ (1.00). Von Bertalanffy growth parameters are L∞ = 526.46, K = 0.28, and t0 = 0.22. The length–weight relationship is described as log W = −5.16 + 3.03 log L. Fulton’s condition factor increases with fish length, from 0.70 to 0.83. Regarding seasonal fluctuations, this factor begins to increase in late spring, with the trend continuing until autumn, and then decreasing from autumn to spring.

Fish spawning habitat availability in the river Waal is significantly influenced by seasonal and annual variations in discharge. In this paper we develop habitat suitability models, based on a literature survey of spawning preferences of the commonly occurring species roach (Rutilus rutilus), bream (Abramis brama), pikeperch (Sander lucioperca) and bleak (Alburnus alburnus). Within the resulting models water depth, flow velocity, water temperature and vegetation type were the most significant environmental parameters. Spatial data for the parameters were derived from a 2-D hydrodynamic model and detailed monitoring database. The area of suitable habitat available for spawning was calculated using the HABITAT software, based on species-specific suitability models and the environmental characteristics of two study sites on the river Waal over a 3 year period (1997-1999). The predicted available spawning area was compared with field data on the recruitment of young fish of each species for the same years and locations. There was a positive relationship between predicted available habitat and observed young of the year (YOY) densities for bream, roach and pikeperch. A negative relationship was recorded between predicted available area and observed YOY densities for bleak. The results indicate that optimal hydrological and hydraulic conditions differ even for species that are widely considered eurytopic. Moreover, annual differences in habitat availability indicate a strong influence of hydrological variability on population dynamics.

At the end of the first half of the 20th century, 61 species and subspecies of fish, including one invader (bleak Alburnus alburnus) and 17 species—endemics of Baikal—were reported for Siberia (Berg, 1933, 1949). At the present time, in rivers, lakes, and reservoirs of Siberia, 96 fish species and subspecies are described, of which 80 are aboriginal and 16 are invaders; 33 species are endemics of Baikal. Each landscapegeographic zone of Siberia has its specific ichthyofauna: in rivers and lakes of the south of Siberia, species of boreal piedmont complex dominate; in water bodies of the steppe, forest-steppe, taiga, and southern parts of the forest-steppe zone boreal plain dominates; in the zone of tundra, arctic freshwater dominates; and in Baikal, the most part (35) of species belongs to the Baikal autochtonous complex. Most researchers, as before, distinguish in Siberia two ichthyogeographic sites—West Siberian and East Siberian—that enter the Arctic Province of the Circumpolar subregion of the Holarctic region. Baikal is considered in the rank of the suboblast of the Holarctic.

During parasitological investigations of the gills of 3 cyprinid species from lakes from the Adriatic river basin of Macedonia (Lake Ohrid and Lake Prespa), 7 monogenean species were found: in Chondrostoma nasus we found: Dactylogyrus elegantis, D. vistulae and Paradiplozoon homoion homoion, in Alburnus alburnus we found Dactylogyrus alatus f. typica, Dactylogyrus minor, Diplozoon paradoxum and Paradiplozoon alburni, in Alburnoides bipunctatus we found Dactylogyrus alatus f. typica and Paradiplozoon alburni. Prevalence in Chondrostoma nasus ohridanus is 50,0%, in Chondrostoma nasus prespensis is 41,59% (in total Chondrostoma nasus - 41,88%), in Alburnus alburnus ohridanus is 47,75%, in Alburnus alburnus prespensis is 41,38% % (in total Alburnus alburnus - 44,95%), in Alburnoides bipunctatus ohridanus is 35,14%), in Alburnoides bipunctatus prespensis is 11,54% (in total Alburnoides bipunctatus - 29,0%). The most frequent monogeneans found in the fishes from both lakes are: Dactylogyrus alatus f. ty...

The population status of bleak (Alburnus alburnut (L.) in sand-pit lake Chepintsi near Sofia by using some biological factors as growth rate, condition and fecundity was investigated. The maximum a...

The Cinca River is a tributary of Ebro River in the NE of Spain which receives input from different activities. One of the most important is related to an industry where DDT is used as an intermediate in the production of dicofol. This study evaluated the DDT contamination along the Cinca River. Sampling sites were selected up- and downstream from this industry. Sediments and fishes (59 bleaks (Alburnus alburnus) and 23 barbels (Barbus graellsi)) were collected in 2002 and analyzed using a new and rapid selective pressurized liquid extraction (SPLE) method. DDT and its metabolites were found in sediments and fishes at levels ranging from 9 to 94microg kg(-1) dry weight (d.w.) and from not detected to 2098microg kg(-1) wet weight (w.w.), respectively. The highest values corresponded to samples collected just downstream the industry. Thirty kilometers downstream from the factory, levels were clearly lower, showing a weakening of the impact. p,p'-DDE isomer comprised up to 50% and 70% of total DDT measured in sediment and fish, respectively. When compared with values obtained in a previous study in 1999, a generalized drop of the levels in all matrixes (77-97%), was observed. No meaningful differences were found between the two fish species studied neither between the two tissues (muscle and liver) analyzed.

Prescribed or natural drawdowns occur frequently in reservoirs but their effects on fish populations have been barely studied. As a consequence of a severe drought and the need to optimize water quality, a partial drawdown was prescribed in autumn 2005 to a eutrophic reservoir that provides water supply to a large metropolitan area (Barcelona, Spain). In order to avoid a potential massive fish kill given the reduced oxygen availability and high fish abundance, preventive purse seine fisheries were performed to reduce the fish stock. The fisheries had little effect on the fish assemblage because final population size structure and species composition did not change significantly. The species composition of the purse seine catches varied significantly during the drawdown with higher proportion of bleak (Alburnus alburnus) in pelagic water during the days of worst water quality, confirming that bleak is more tolerant than roach (Rutilus rutilus) to poor water quality and a potential good indicator of water pollution. The weight–length relationship (i.e. condition) of roach and bleak also varied significantly during the drawdown following the same tendency in both species, losing and recovering their weight (4.99% in roach and 5.96% in bleak) in only 16 days. The close relationship found between water quality and fish condition demonstrates that fish condition can be a good metric of the well being of fish, even for extreme short-term changes.

We investigated interspecific differences in the downstream drift of seven species of young-of-the-year cyprinids over a 2-year period in two central European rivers, using a comparison of drifting fish with fish collected from nurseries at the same time and the same site as the drift samples. Species varied in the utilisation of the drift; Rutilus rutilus, Gobio spp., Abramis brama and Carassius auratus gibelio drifted abundantly, while Leuciscus cephalus and Alburnus alburnus were abundant in nurseries, but drifted at low densities. Abramis bjoerkna was equally represented among drifting and resident fish. Generally, fish drifted at two major developmental intervals; L3 stage and the stage at transition between larval and juvenile periods (L6/Juv), with interspecific differences in the ontogenetic timing of drifting. The propensity to drifting of certain developmental stages was also reflected in body size comparisons between drifting and resident fish. The stage-dependent drifting may be attributed to major changes in fish morphology, behaviour and swimming ability.

Recently, Wurtsbaugh (2007) commented on our earlier report in which we quantified the nutrient subsidy by a facultative insectivorous fish (bleak, Alburnus alburnus) feeding on terrestrial insects in a 0.12 km2 lake (Groser Vatersee, Germany) (Mehner et al. 2005). We showed that the annual consumption rate of bleak consisted of about 84% terrestrial insects. We estimated that the allochthonous phosphorus included in these insects represented about 2.1% of the lake’s internal total phosphorus (TP) concentration, whereas excretion of P by fish was equivalent to about 11% of the mean epilimnetic soluble reactive phosphorus (SRP) concentration. Accordingly, we concluded that the lake studied was only weakly subsidized by allochthonous phosphorus stored in insects. Based on a decay model with varying parameters that calculated the spatial distribution of the daily fallout of terrestrial insects into lakes, we concluded that the subsidy by terrestrial insects to fish consumption and lake nutrient pools was likely most important in small, oligotrophic lakes surrounded by forests. Wurtsbaugh identified three possible shortcomings in our analyses. First, he argues that insects consumed by fish 3 Present address: European Commission, DG Joint Research Centre (JRC), Institute for the Protection and Security of the Citizen (IPSC), Agriculture and Fisheries Unit, TP 051, I-21020, Ispra, Italy. 2 Present address: Institut fur Systematische Zoologie, Museum fur Naturkunde, Humboldt-Universitat, Invalidenstrase 43, D10115 Berlin, Germany.

Since its first record in a tributary of the Ebro basin in 1992, the bleak Alburnus alburnus has spread to almost the whole Iberian Peninsula. In this paper (based on electrofishing surveys in 598 localities), we provide information on the expansion of the bleak. We detail current distribution in the Ebro basin and the rivers of the Eastern Pyrenees and we report its presence in three other major Iberian drainages. Currently, the bleak is sympatric with 15 Iberian endemic species (58% of total Iberian endemic fish). The possible threats to the rich Iberian ichthyofauna caused by the presence of the bleak are discussed. The factors that promoted the extremely rapid expansion of this exotic cyprinid are examined, focusing on the role of reservoirs, which seem to favour its dispersal.

In 1997, faeces samples (spraints) (n = 175) from the European otter (Lutra lutra) were taken in seven localities of the El-Kala region. This is a restricted eco-geographic complex in which freshwater hydrographical systems, comprising rivers, ponds and wet coastal zones (brackish lagoons, shipping channels), are highly interwoven. The frequency of occurrence and relative abundance of consumed taxons were calculated on the basis of 493 identified prey. Fish made up more than 88% of the otter’s catch (relative abundance), with a strong predominance of Pseudorasbora parva, Luciobarbus callensis and undetermined Cyprinidae. Anuran amphibians made up 9% of the prey. The remainder were represented, in order of significance, by mullets, eels (Anguilla anguilla), bleaks (Alburnus alburnus), perciformes, gobies, insects, birds, crustaceans, etc. However, Cyprinidae, the eel and the barbel dominated in terms of ingested biomass. The otter’s diet varies with local conditions : lagoons and channels have marine or migratory fish ; rivers are dominated by barbels ; ponds by Cyprinidae. Finally, small-sized fish (topmouth gudgeon and barbel) dominated the diet in terms of numbers : 62% are smaller than 12.5 cm. The introduction of the topmouth gudgeon into the region could have catastrophic consequences for endemic fish, such as Pseudophoxinus callensis., En 1997, des échantillons de fèces (épreintes) (n = 175) de la loutre d’Europe (Lutra lutra) ont été récoltés dans sept localités dans la région d’El-Kala. C’est un complexe écogéographique restreint où les systèmes hydrographiques dulcicoles, constitués de rivières, d’étangs et de zones humides littorales (lagunes saumâtres, chenaux maritimes), sont assez imbriqués. Les fréquences d’occurrence et l’abondance relatives des taxons consommés ont été calculées à partir des 493 proies identifiées. Les poissons constituent plus de 88 % des prises (abondance relative) avec une très large prédominance de Pseudorasbora parva, Luciobarbus callensis et des cyprinidés indéterminés. Les amphibiens anoures constituent 9 % des proies. Le reste est représenté, selon l’importance, respectivement par des mugilidés, des anguilles (Anguilla anguilla), l’ablette (Alburnus alburnus) des perciformes, des gobiidés, des insectes, des oiseaux, des crustacés... Cependant, les cyprinidés, l’anguille et le barbeau dominent pour la biomasse ingérée. Le régime alimentaire est fonction des conditions locales : les lagunes et chenaux avec des poissons marins ou amphihalins ; les rivières où dominent les barbeaux ; les étangs avec les cyprinidés. Enfin, les poissons de petite taille (pseudorasbora et barbeau) dominent le régime en nombre : 62 % font moins de 12,5 cm. L’introduction de pseudorasbora dans la région pourrait être catastrophique pour des poissons endémiques, comme Pseudophoxinus callensis., Libois Roland, Ghalmi Rachida, Brahimi Amina. Insight into the Dietary Habits of the Eurasian Otter, Lutra lutra, in the East of Algeria (El-Kala National Park). In: Ecologia mediterranea, tome 41 n°2, 2015. pp. 85-91.

The fish community of a channelized stretch of a lowland floodplain River Morava (Danube basin) was surveyed before and after an exceptionally extensive flood in July 1997. Water discharge peaked at 2,000% of long-term average and discharge > 1,000 % lasted for 20 days. Electrofishing survey along the bank in three inter-weir reaches revealed 26 species, with the same species (chub Leuciscus cephalus, gudgeon Gobio gobio) dominating before and after the flood. The flood had a minor effect on the assemblage structure. The total density of fish was not significantly different before and immediately after the flood. The largest decline was observed for pelagic species (e.g. bleak Alburnus alburnus, roach Rutilus rutilus) and benthic species (e.g. barbel Barbus barbus). The overall gudgeon abundance did not decrease significantly after the flood, though length-frequency distribution revealed a decrease in abundance of one-year-old individuals. The flood had no effect on abundance of chub and burbot (...

The acute effects of a herbicide based on 2,4-D on embryos and larvae of bleak, Alburnus alburnus L. exposed to concentrations of 25–3200 mg 1−1 for 12–48 hours were investigated. The 2,4-D delayed or stopped the development of embryos in their early stages, caused behavioural changes and morphological alterations. The L.C.50 values for embryos varied between 12–9 and 15·9–4mg 1−1 and for larvae from 51·6 to 111·2mg 1−1 according to the time of exposure. The level of 2,4-D in Lake Balaton, or similar shallow lakes, without substantial injury of the littoral fish fauna should not surpass 0·5–1·0 mg 1−1.

Sensitiveness to the overall influence of the river channel regulation, impoundment and pollution was studied for 12 non-obligatory riverine (NOR) fish species in the Warta River, Poland, over the period of 1963–1998. Their total abundance has not considerably changed unlike the structure of their aggregation, which was revealed by a self-organizing map (SOM, Kohonen unsupervised artificial neural network) almost perfectly separating 1960s samples from 1990s ones. The greatest changes in proportion were recorded for the dominant roach Rutilus rutilus (from 28.6 to 60.0%), perch Perca fluviatilis (1.9 to 9.5%), pike Esox lucius (2.9 to 4.9%), and the former codominant bleak Alburbus alburnus (22.9 to 1.8%). They resulted from highly significant (p < 0.001), reaching even one order of magnitude, differences in the abundance of these species. Such remarkable alternations in dominant NOR ichthyofauna obviously influenced the whole fish assemblage structure, which was best illustrated by a clear vertical gradient over SOM in Simpson and Shannon indices. Thus, NOR species, both studied together and separately, can supply valuable information on the fish assemblage dynamics and should not be neglected in temporal analyses, often focused only on vulnerable obligatory riverine, migratory and/or endemic species.

We estimated consumption and excretion rates of terrestrial-borne phosphorus by a population of the insectfeeding fish species bleak (Alburnus alburnus) in a 0.12-km 2 mesotrophic lake of the German lowlands. Fish abundance, growth rates, and diet composition were determined, and consumption and nutrient metabolism were calculated by a bioenergetics model. Mean bleak abundance was about 77,000 ind. km 22 . About 84% of bleak consumption consisted of terrestrial insects. Annual consumption of lake-external phosphorus (P) by bleak was 432 g, representing ;2.1% of the lake internal P-pool. Annual excretion of terrestrial-derived phosphorus by bleak was equivalent to ;11% of the mean epilimnetic SRP concentration. A substantial subsidy of lake nutrient pools by insectivorous fish is more likely in lakes ,0.03 km 2 owing to the increasing perimeter-to-area ratio between donor and recipient habitats. Terrestrial nutrient subsidy by fish feeding may be important only in small oligotrophic lakes in forested areas.

The large-scale spatial distribution of fish was investigated within a morphometrically simple canyon-shaped reservoir with a single major tributary and a longitudinal trophic gradient (Řimov Reservoir, Czech Republic). Samples of fish were taken by Nordic survey gill nets (several mesh sizes from 8 to 70 mm knot to knot) installed as surface nets at several offshore areas located along the longitudinal axis of the reservoir. Surveys were carried out in late summer during 1999–2003. An obvious distribution gradient of fish was revealed along the longitudinal axis of the Řimov Reservoir. The total relative fish abundance and biomass (catch per unit effort) decreased considerably from the upstream end of the reservoir toward the dam. Roach (Rutilus rutilus), bleak (Alburnus alburnus) and bream (Abramis brama) comprised the bulk of catches at all areas. Enhanced dominance of bream was observed in the fish assemblage at the uppermost, more eutrophic area of the reservoir. The highest number of fish species and the highest abundance of young-of-the-year fish were also observed in the tributary area. In the downstream part of the reservoir, gill net surveys along the vertical depth profiles indicated that offshore fish occupied mostly the epilimnion. Extreme flood events affected the Řimov Reservoir, however, it seemed they had no significant impact on the gradients described. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The variations in the vertical migrations by zooplankton and food composition of fish in the shallow, clay-turbid Mustionselka basin of Lake Hiidenvesi were studied (water depth 3 m). Daphnids showed signs of reverse migration, their density in the surface layer being highest during the day. The reverse migration was probably due to predation threat by the predatory cladoceran Leptodora kindtii. Chydorus sphaericus, which was consumed especially by the day active bleak (Alburnus alburnus), showed normal vertical migration. Copepods showed no clear vertical movements. Leptodora kindtii, as well as the large herbivore Limnosida frontosa, showed no vertical migrations, but their overall abundance increased considerably during the night, indicating horizontal movement towards the open water at night. Due to the shallowness of the water, vertical migrations may not be a good predator-avoidance strategy for the largest cladocerans, which may be able to perform horizontal migrations. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The hybrid Leuciscus cephalus ? Alburnus alburnus was recognized in studying structure of the ichthyofauna of the middle course of the Ibar River, a right-hand tributary of the Western Morava (system of the Danube on the territory of Serbia). It is a hybrid reciprocal to the natural hybrid Alburnus alburnus ? Leuciscus cephalus from the same river system (the Gruza River, a left-hand tributary of the Western Morava), which was described previously by the present author. The hybrid was identified on the basis of its intermediate characteristics and characteristics of the parent species such as pharyngeal bones and teeth; shape of the scales; number, form, and structure of radial canals of the scales; morphology of branchiospinae on the first gill arch; and a complex of meristic and morphometric characters. With respect to its characteristics, this hybrid, like the hybrid Alburnus alburnus ? Leuciscus cephalus, is closer to L. cephalus. However, in general appearance the hybrid more closely resembles the presumed maternal species. The phenomenon of reciprocal hybridization is discussed at some length.

Summary The aim of this study was to analyse the genetic structure of populations for seven common cyprinid fish species within a 120-km-long stretch of the lowland Elbe River, northern Germany. The results are needed for habitat modelling to estimate the proportion that environmentally based variance has of the total variances of home range, species distribution, habitat use and fish assemblage structure. Polymerase chain reaction (PCR)-fingerprinting offers a rapid, efficient method for generating genetic markers and was therefore used to obtain an overview on population-genetic structures of the following seven fish species: asp (Aspius aspius), bleak (Alburnus alburnus), blue bream (Abramis ballerus), common bream (Abramis brama), gudgeon (Gobio gobio), ide (Leuciscus idus) and roach (Rutilus rutilus). Of the 20 random primers, between eight (ide) and 18 (roach) produced polymorphic bands. The mean levels of genetic similarity between samples, estimated as bandsharing frequencies, varied between 76% in bleak and 98% in asp. The corresponding genetic distances among samples varied between 0.02 ± 0.01 in asp and 0.24 ± 0.09 in bleak. The genetic distances among samples were not significant in all of the pairwise comparisons, and correlated only weakly with the geographic distances among sampling sites. It was therefore concluded that the stretch of the Elbe surveyed was inhabited by single, panmictic populations of the species studied and thus that the observed habitat preferences, fish distribution, home range and ecological performance of species within this area will depend on stochastic environmental factors or result from biotic interactions.

– Movements of fish, in particular roach Rutilus rutilus, perch Perca fluviatilis, rudd Scardinius erythrophthalmus, bleak Alburnus alburnus and chub Leuciscus cephalus (age ≥ 1+) in relation to environmental variables were examined between the River Morava, Czech Republic, and a rehabilitated former meander. Data were taken over seven 24-h periods in April–June 1997 using two back-to-back traps. Of 170 fish captured, 70% moved from the backwater to the river. Diel activity differed between sampling dates, but overall bleak, roach and chub moved mainly between dusk and dawn, whereas perch moved throughout most of the day. Rudd showed bi-modal (mid-day, midnight) activity. However, avoidance behaviour could have biased results for species known to be wary of traps. Water level changes, temperature and illumination were among the main environmental factors influencing fish movement, along with spawning migrations relevant for most species. In all specimens, over 65% individuals captured were ready to spawn. Most of them, except for perch, were moving out of the backwater towards the river.

st young-of-the-year (YOY) fishes in two lowland rivers in the Czech Republic (Danube Basin) drifted from mid-May to mid-July and almost exclusively at night. The peak of drift density lasted c. 3 weeks and depended on water temperature (by its effect on fish spawning), but not on discharge. Peak drift densities varied between years and rivers from 80 to 1354 fish 1000 m−3. More than 98% of drifting fish were cyprinids. Rutilus rutilus, Rhodeus sericeus, Gobio spp., Alburnus alburnus and Abramis brama were dominate in the 22 species encountered in the River Morava. Carassius auratus gibelio and R. sericeus were the most common of 17 species in the River Kyjovka. Species composition of drifting fishes was similar among years in the Morava but varied in the Kyjovka. The species composition of drifting fishes did not differ from those of the YOY fish assemblage in nursery areas during the drift season. Relative abundances in nursery areas decreased after the drift season in species that dominated in the drift, but increased in those that avoided drift. It is suggested that drift is a regular part of the life history of many cyprinid fishes and interannual variability in density and species composition of drifting YOY fish can be explained by variable spawning success among years. Differences in the relative abundances of the YOY fish assemblage in nurseries during and after the drift season suggests that drift may cause significant mortality.