Chondrostoma Polylepis Research Articles

New evidence of alternative migration patterns for two Mediterranean potamodromous species

Iberian barbel (Luciobarbus bocagei Steindachner, 1864) and Iberian nase (Pseudochondrostoma polylepis Steindachner, 1864) are two Mediterranean potamodromous fish species known to perform annual upstream migrations to reach spring spawning grounds. In the Mondego River basin, at the Coimbra dam, migratory movement patterns and individual size structure were assessed through a video recording monitoring system installed on an upstream section of a vertical-slot fish pass. Visual census for these target species during two consecutive annual cycles (2013–2014) revealed alternative migratory patterns, with the first peak of upstream movements in autumn, for both barbel (October–November) and nase (November–December). Circadian movements of both species showed a diurnal preference, contrary to what is usually described for these species. Size structure analysis for individuals of both species showed significant intra-annual differences in the size of migrating fish. Boosted regression trees models applied to the 2013–2014 visual count data identified flow and temperature as the most influential environmental predictors, triggering both species’ movements in each direction in the study years. These results provide novel information on the timing of the migratory movements of these potamodromous fish, which can be used to adapt current management and conservation measures to the specificities of their migratory behaviour.

Distribution and diet of recovering Eurasian otter (Lutra lutra) along the natural-to-urban habitat gradient (river Segura, SE Spain)

In the catchment of the River Segura (SE Spain), ongoing Eurasian otter (Lutra lutra) recovery and concurrent spread of human settlements are resulting in increasing otter records into urban areas. We analysed otter diet along a natural-to-urban gradient, with the main aim of assessing to which extent man-driven variation in food availability affects its feeding habits and how this secretive mustelid can thrive in apparently unsuitable habitats. From 2016 to 2019, we collected 521 spraints, monitoring 37 sampling stations (mean length ± SD = 0.5 ± 0.3 km). In natural areas, the percent cover of undisturbed banks was the highest, with the lowest number of water abstraction systems, whilst water pollution was the highest in urban areas. Introduced red swamp crayfish (Procambarus clarkii) and fish formed the bulk of otter diet. The two most preyed fish, Luciobarbus sclateri and Pseudochondrostoma polylepis, were among the most abundant species in the river, confirming the generalist feeding behaviour of the otter. The contribution of non-native fish was on average low, while invasive crayfish exceeded the overall importance of fish in all habitats except urban areas. Overall, diet data did not allow attesting food as a limiting resource for otters in urban areas. In contrast, marking intensity varied consistently with the natural-to-urban gradient (from 0.31 to 0.65 spraints/100 m in urban- and natural areas, respectively), suggesting that human disturbance (i.e. habitat modification and water pollution) may play a major role in shaping otter distribution.

Can vegetation provide shelter to cyprinid species under hydropeaking?

A novel study that focuses on the capacity of vegetation to provide shelter for fish species under hydropeaking regimes is presented. Two artificial patches mimicking the structure and density of Carex sp. mats were installed in an experimental flume to test whether submerged plants can offer flow refuge to two cyprinid species, Luciobarbus bocagei and Pseudochondrostoma polylepis, under baseflow and hydropeaking scenarios. Local flow fields were characterized using a Lateral Line Probe (LLP) and an Acoustic Doppler Velocimeter (ADV) and 33 h of video analysis were viewed to report, on a per-second basis, fish use of 1) patches with plants, 2) patches upstream and 3) downstream from vegetation and 4) patches without vegetation. Data on flow fields and fish patch use were integrated and analyzed to assess whether plants favored fish sheltering behavior. Vegetation created hydraulically stable areas suitable for fish to shelter, triggering changes in fish patch use. Although both species sheltered under hydropeaking, L. bocagei presented a stronger preference than P. polylepis for vegetated patches and areas downstream from plants, taking advantage of sheltered regions more frequently. P. polylepis weaker search for shelter could be related to species-specific factors and territorial behavior interferences rather than to fish performance relative to flume hydraulic conditions. Despite a weaker response, some P. polylepis individuals used patches downstream from plants more during the second half of the hydropeaking trials. A trade-off between reducing swimming effort and territoriality might explain this response. Results indicate that vegetation can help to counterbalance the impact of hydropeaking on fish while providing river functioning benefits. Evaluating fish sheltering to a wide set of river plants and patch designs on a species-by-species basis would help targeting vegetation-based actions for restoring hydropeaking rivers.

Passage Performance of Technical Pool-Type Fishways for Potamodromous Cyprinids: Novel Experiences in Semiarid Environments

Endemic freshwater fish from semiarid environments are among the most threated species in the world due to water overexploitation and habitat fragmentation problems. Stepped or pool-type fishways are used worldwide to reestablish longitudinal connectivity and mitigate fish migration problems. Many of them are being installed or planned in rivers of semiarid environments, however, very few studies about fish passage performance through pool-type fishways has been carried out to date on these regions. The present work focuses on the passage performance of two potamodromous cyprinids endemic of these regions, with different ecological and swimming behavior: southern Iberian barbel (Luciobarbus sclateri) and Iberian straight-mouth nase (Pseudochondrostoma polylepis). These are assessed in two of the most common types of stepped fishways: vertical slot and submerged notch with bottom orifice fishways. Experiments were carried out during the spawning season in the Segura River (southeastern Spain), using a passive integrated transponder (PIT) tag and antenna system. Ascent success was greater than 80%, with a median transit time lower than 17 minutes per meter of height in all trials, and for both species and fishway types. Results show that both types of fishways, if correctly designed and constructed, provide interesting alternatives for the restoration of fish migration pathways in these regions.

Structural microhabitat use by endemic cyprinids in a Mediterranean‐type river: Implications for restoration practices

Abstract Endemic freshwater fish from the Mediterranean region are among the most threatened species in the world owing to increasing river degradation. Because of such threats, the number of river restoration projects has greatly increased. However, they are seldom planned with consideration of the species' life history, often resulting in erroneous practices that compromise their success. This study assessed the seasonal and size‐related microhabitat use by three endemic cyprinids (Iberian barbel, Luciobarbus bocagei; Iberian straight‐mouth nase, Pseudochondrostoma polylepis; and calandino, Squalius alburnoides) using a modified point electrofishing procedure in a Mediterranean river. A multivariate approach was then employed to analyse both structural resource use and availability data. All species showed non‐random microhabitat use. The barbel and nase shifted to faster‐flowing positions (>25 cm s−1) with a coarser substratum (>150 mm particle size) during spring and to sheltered positions (50–100% instream cover) during autumn. Calandino selected more covered areas in autumn (>60% cover) and shifted to shallower positions from this season (>40 cm) to summer (<35 cm). Significant size‐related differences in microhabitat use were consistent for the three species, with smaller individuals occupying on average shallower microhabitats. Significant resource‐use overlap between species size classes increased from autumn to summer, occurring mainly between juvenile and small adult barbel and calandino. The present study helped develop recommendations for river restoration practices that may have a wider application, particularly for other Mediterranean‐type rivers. Cover was found to be critical for all species, in particular for calandino, which could be classified as a shelter‐oriented eurytopic species. Restoration scenarios should therefore consider maintaining cover habitats during unfavourable flow conditions for these species. Lithophilic spawners, which were highly responsive to velocity and substratum, could particularly benefit from the creation of gravel bedforms and artificial riffles to enhance depth and flow variability.

Microhabitat competition between Iberian fish species and the endangered Júcar nase (Parachondrostoma arrigonis; Steindachner, 1866)

ABSTRACTCompetition with invasive species is recognized as having a major impact on biodiversity conservation. The upper part of the Cabriel River (Eastern Iberian Peninsula) harbours the most important population of the Júcar nase (Parachondrostoma arrigonis; Steindachner, 1866), a fish species in imminent danger of extinction. Currently, this species cohabits with several non-native species, such as the Iberian nase (Pseudochondrostoma polylepis; Steindachner, 1864) and the bermejuela (Achondrostoma arcasii; Steindachner, 1866). The potential habitat competition with these species was studied by analysing the spatial and temporal overlapping of suitable microhabitats. Generalized Additive Mixed Models (GAMMs) were developed to model microhabitat selection and these GAMMs were used to assess the habitat suitability (i.e. probability of presence) under several flows simulated with River2D. The Júcar nase will compete, spatially and temporally, for the few suitable microhabitats with bermejuela and, to a lesser extent, with small Iberian nase; conversely, large Iberian nase was of minor concern, due to increased differences in habitat preferences. This study represents an important assessment of potential competition and, therefore, these results might assist to better define future management practices in the upper part of the Cabriel River.

Assessing population status of Parachondrostoma arrigonis (Steindachner, 1866), threats and conservation perspectives

Biodiversity is currently declining in the Mediterranean, particularly in freshwater ecosystems. The Iberian Peninsula is not an exception with many fish species threatened or endangered. This is the case of Parachondrostoma arrigonis, which has experienced a marked reduction of more than 80 % in both number and area of occupancy in the last 20 years. Species historical records showed a widespread distribution in the Jucar Basin, but according to recent records, P. arrigonis was completely absent in the main river course, being restricted to only some tributaries. Current fish distribution was grouped into only seven fish population nuclei geographically isolated among them. Only two population nuclei showed with well-developed fish populations. Factors affecting P. arrigonis distribution are associated to human activities, such as river channelization, flow regulation, pollution and habitat degradation, being concentrated in the middle and lower river reaches where the Jucar nase is in marked regression. Another key factor was the presence of introduced species, reporting a strong spatial segregation with the translocated Pseudochondrostoma polylepis, an ecologically similar species, and with the exotic piscivorous Micropterus salmoides and Esox lucius, which are currently occupying most of the P. arrigonis historical range. Because its dramatic situation, conservation measures must be urgently taken, for instance, by establishing conservation areas, an exotic fish removal programme, and by developing a flow regulation program to minimize dam effects. However it is necessary to increase our knowledge regarding the habitat requirements of the Jucar nase and its interactions with invasive species. If measures are not implemented its extinction seems inevitable.

Introgressive hybridization as a promoter of genome reshuffling in natural homoploid fish hybrids (Cyprinidae, Leuciscinae)

Understanding the mechanisms underlying diversification and speciation by introgressive hybridization is currently one of the major challenges in evolutionary biology. Here, the analysis of hybridization between two pairs of Iberian Leuciscinae provided new data on independent hybrid zones involving Achondrostoma oligolepis (AOL) and Pseudochondrostoma duriense (PDU), and confirmed the occurrence of hybrids between AOL and Pseudochondrostoma polylepis (PPO). A multilevel survey combining morphological, genetic and cytogenomic markers on a vast population screening successfully sorted the selected fishes as admixed. Results were similar in both AOL × PDU and AOL × PPO systems. Overall, hybrid morphotypes, cytogenomic data and genetic profiling indicated preferential backcrossing and suggested AOL as a major genomic contributor. Moreover, results implied AOL as more permissive to introgression than PDU or PPO. Although PDU- and PPO-like individuals appeared more resilient to genome modifications, AOL appeared to be more involved and affected by the ongoing hybridization events, as chromosomal translocations were only found in AOL-like individuals. All hybrids analysed evidenced extensive ribosomal DNA (rDNA) polymorphism that was not found in parental species, but usually seen falling within the range of possible parental combinations. Yet, transgressive phenotypes that cannot be explained by normal recombination, including more rDNA clusters than expected or the occurrence of syntenic rDNAs, were also detected. Present results proved rapid genomic evolution providing the genetic novelty for species to persist. In addition, although the ultimate consequences of such apparently extensive and recurrent events remain unknown, modern genome-wide methodologies are of great promise towards answering questions concerning the causes, dynamics and impacts of hybridization.

Assessing inter-drainage connections: patterns of genetic diversity in an Iberian cyprinid fish

The phylogeography of Iberian freshwater fish species strongly reflects the geomorphological history of Iberian water drainages and formation of mountain ranges. In particular, the Iberian Central Massif limits two ichthyogeographical districts based on fish distribution assemblages: the Northwest district, which comprises all river basins north of the Central massif, and the Central-west district, which comprises the Tejo and Sado basins. Despite this scenario, the cyprinid Pseudochondrostoma polylepis occurs in both the Tejo and Mondego rivers (one either side of the Estrela Mountains, in the western end of the Central Massif). By analysing the population structure and demographic history of this straight-mouth nase, based on both mtDNA and microsatellites, we have found evidence of a relatively recent common origin for both Mondego and Tejo populations. Shared haplotypes and lack of divergent lineages for mitochondrial marker, high levels of admixture and common ancestry at the nuclear level, together with signatures of asymmetrical gene flow from Tejo to Mondego suggest a Mondego colonization through a founder event with an origin in Tejo. We suggest that this colonization might have resulted from the occurrence of river connections/captures between Mondego and Tejo headwater tributaries in the recent past. With this study we reinforce that local-scale geomorphological events and the adaptation/dispersal ability of a species to new environments can have a major impact on its demographic history, colonization processes, and ultimately its distribution. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109, 656–669.

UNCERTAINTY IN PREDICTING THE FISH‐RESPONSE TO TWO‐DIMENSIONAL HABITAT MODELING USING FIELD DATA

ABSTRACTBoth water managers and researchers have the same goal when it comes to fish conservation, namely, to sustain, to improve or to restore aquatic habitat. To this aim, two‐dimensional (2D) hydrodynamic models have been widely used in aquatic habitat studies because they simulate flow with high accuracy and can predict habitat dynamics. The River2D model is able to integrate the habitat suitability curves for fish life stages with the simulated depth and velocity fields and the riverbed characteristics of substrate and cover, thereby estimating the corresponding weighted usable area, and thus predicting the potential distribution of fish species in the river. However, little is known about the in situ variability associated with such predictions both for hydraulic and biological data, whereas ecological responses are known to be driven by variability. Moreover, when calculating habitat availability, differences can be found by considering in the weighted usable area formulation substrate or cover or even both. To test the level of predictive accuracy of hydraulic and biological simulations, we modelled the habitat use by two fish species, the Iberian barbel Luciobarbus bocagei and the Iberian straight‐mouth nase Pseudochondrostoma polylepis, according to their requirements for depth, velocity, substrate and cover and then compared measured and simulated hydraulic and biological outcomes using the River2D model. Results indicate that 2D simulation depends on data collection, especially the density and location of bed topography points. Substantial differences were found in the biological responses. Results may differ when choosing different habitat availability variables. Similarly, habitat use may also be influenced by other biotic and abiotic interactions occurring in ecosystems, and restoration planning should be aware of such variability. Copyright © 2012 John Wiley & Sons, Ltd.

Population genetic structure in the Iberian cyprinid fish Iberochondrostoma lemmingii (Steindachner, 1866): disentangling species fragmentation and colonization processes

Interplay between the complex geography, hydrogeomorphological history, past climatic changes, and anthropogenic pressures is likely responsible for the current diversity and species' distribution of freshwater fishes in the Iberian Peninsula. To further disentangle the evolutionary processes promoting the diversification of endemic Iberian Cyprinids through time and space, we explored the patterns of genetic diversity of the Iberian arched‐mouth nase, Iberochondrostoma lemmingii (Steindachner, 1866), using molecular markers rendering at different timescales: the mitochondrial gene cytochrome b and seven microsatellite loci. Both markers showed significant differentiation of populations though the relative genetic distances among populations were different between markers. Mitochondrial DNA results indicate the isolation of hydrographic basins as the main driver of population differentiation, with Tejo as the centre of diversification. The results also support connections between Tejo, Guadiana, and Guadalquivir, with levels of divergence suggesting an earlier severance of Guadalquivir, whereas Guadiana and Tejo maintained connections until a more recent past. Establishment of more peripherial populations in small southern basins (Quarteira and Almargem) could have been ruled by founder events. However, the analysis of present‐day genetic configuration suggested by microsatellite data implies, for the first time, the involvement of other factors in the evolution of arched‐mouth Iberian nase populations. Relative low genetic distances between inter‐basin populations (Tejo and Guadiana) and the lack of concordance between differentiation and geography suggest a possible influence of human‐mediated translocations in the population genetic patterns of I. lemmingii. High intra‐basin differentiation levels were found within Tejo and Guadiana and may be associated with factors intrinsic to the species (e.g. low dispersal capability) or natural and/or artificial barriers to gene flow. The low vagility of the species appears to be an important factor influencing the evolutionary processes shaping the phylogeographical patterns of I. lemmingii, which could be relevant for the conservation of this threatened species. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105, 559–572.

Swimming performance of two Iberian cyprinids: the Tagus nase Pseudochondrostoma polylepis (Steindachner, 1864) and the bordallo Squalius carolitertii (Doadrio, 1988)

Summary The main purpose of this study was to gather swimming performance information for two endemic cyprinids of the Iberian Peninsula to contribute to the optimization of fish ways. Critical swimming speed (Ucrit) was determined for the Tagus nase Pseudochondrostoma polylepis (Steindachner, 1864) and for the bordallo Squalius carolitertii (Doadrio, 1988) in a swimming tunnel. From a total of 80 P. polylepis tested, the mean (± SD) Ucrit observed was 0.78 ± 0.15 ms−1 (c. 3.74 ± 0.93 BL s−1); the 68 S. carolitertii tested presented an Ucrit of 0.54 ± 0.1 ms−1 (c. 4.43 ± 0.74 BL s−1). Significant interspecific differences were found between the Ucrit of the tested cyprinids. Intraspecific comparisons between the Ucrit and the variables of size, sex, condition factor and gonado-somatic index were also made. No sex-or gonad maturation-related differences between the Ucrit were identified, but the robust P. polylepis were found to be stronger swimmers. Water velocities in fish ways for P. polylepis and S. carolitertii should aim, on average, for lower than 0.7 and 0.5 ms−1, respectively.

Complex size-dependent habitat associations in potamodromous fish species

Knowledge of the distribution of species life stages at multiple spatial scales is fundamental to both a proper assessment of species management and conservation programmes and the ability to predict the consequences of human disturbances for river systems. The habitat requirements of three native cyprinid species—the Iberian barbel Barbus bocagei Steindachner, the Iberian straight-mouth nase Pseudochondrostoma polylepis (Steindachner), and the Northern straight-mouth nase Pseudochondrostoma duriense (Coelho)—were examined at 174 undisturbed or minimally disturbed sites in 8 river catchments across western Iberia, by modelling occurrence and counts of species life stages at two spatial scales—large (regional) and instream (local)—using hurdle models. All the life stages of the barbel showed a negative association with upstream high-gradient river reaches, whereas juvenile P. duriense favoured such areas. Stream width and openness were negatively related with the occurrence of juvenile and small adult barbel, but not with large adults. Juvenile nase, on the other hand, were found to be mainly confined to fast-flowing habitats with high instream cover and coarser substrata. Advanced life stages of the barbel were mainly associated with the “pure” regional and shared components, whereas the purely local attributes accounted for much of the model variation among nases, in particular juveniles, and juvenile barbel. The results of this study are useful for setting or refining management goals, and highlight the need to separately consider life stages when performing conservation-related studies of species distribution.

Diet of the otterLutra lutrain an almost pristine Portuguese river: seasonality and analysis of fish prey through scale and vertebrae keys and length relationships

AbstractThe seasonal diet and size of fish prey of the otterLutra lutrawere studied in an almost pristine river of North Portugal (Paiva river) through the analysis of spraints collected during 1 year. To identify Iberian freshwater fish species (Salmo trutta,Micropterus salmoides,Lepomis gibbosus,Luciobarbus bocagei,Cyprinus carpio,Carassius auratus,Pseudochondrostoma polylepis,Achondrostoma arcasii, andIberocypris alburnoides) consumed by the otter keys based on scales and vertebrae were first developed and tested. Both keys allowed identification of all fish species, although three Cyprinidae species could not be discriminated (P. polylepis,A. arcasii, andI. alburnoides). Regression equations were calculated to estimate the dimensions of preyed fish. Highly significant linear relationships were obtained for the standard length versus vertebrae measurements, for all fish species, except forC. carpio. Fish was the predominant prey category in autumn and winter, but the otter also preyed on amphibians, reptiles, mammals, and birds, particularly during spring and summer. In general, the otter consumed high proportions of small size fish (3–12 cm for the three indiscriminate Cyprinidae, 3–9 cm forC. carpio, and 6–12 cm forS. trutta).

Cytogenetic survey of species of two distinct genera of Iberian nases (Cyprinidae, Leuciscinae) that hybridize extensively in nature. I. Evidence of a similar and conserved chromosome pattern with some few species-specific markers at macro-structural level

Pseudochondrostoma duriense and Pseudochondrostoma polylepis hybridize extensively with Achondrostoma oligolepis in natural populations. In this first survey, karyotypes were comparatively analyzed by C-, AgNOR- and CMA(3)-banding procedures in pure (non-introgressed) fish specimens. Leuciscinae pattern was evidenced in the three species: metacentrics and submetacentrics dominance, a big subtelo/acrocentric (marker) chromosome pair and a 2n = 50; small macro-structural differences were observed. Heterochromatin was centromere-associated. Exceptions were found at sm1 and st/a1 long arms and at m1, sm3 and sm6 short arms. The st/a1 band was telomeric in the straight-mouth nases and sub-terminal in A. oligolepis. Multiple NORs of heterochromatic nature were found in sm pairs of the three species. Signals were telomeric except for one pair in A. oligolepis. Two to four structural and two functional NORs were found in P. duriense and P. polylepis, and four to six structural and four functional NORs in A. oligolepis. Species-specific markers will prove useful in hybrid zones' cytogenetic characterization and for in-depth studies of genome compatibility-related issues in future studies.

Redistribution of the geographical ranges of the Iberian cyprinid genus Pseudochondrostoma based on a phylogenetic analysis: implications for the historical rearrangements of the north‐western Iberian drainages

A new distribution range is proposed for Pseudochondrostoma polylepis and Pseudochondrostoma duriense based on the phylogeny of two nuclear and one mitochondrial gene sequences, with implications on the geographic history of the north-western Iberian drainages.

Microhabitat use by three endemic Iberian cyprinids in Mediterranean rivers (Tagus River Basin, Spain)

Abstract Microhabitat use by three endemic Iberian cyprinids, Barbus bocagei (Steindachner), Pseudochondrostoma polylepis (Steindachner), and Squalius pyrenaicus (Günther) was studied in terms of depth, mean water column velocity, focal height, focal velocity, distance to shore and substrate. Data were obtained by snorkelling during spring and summer at nine sites of the Tagus River Basin, Spain. Habitat suitability criteria (HSC) were calculated, including fish position and focal velocity in the water column. Species comparison showed differences in depth and focal height (indicating a vertical segregation), and greater water velocities for Pseudochondrostoma. Size‐class comparisons mainly showed differences in depth and focal height (correlated with fish size). The fish groups (3 species × 3 length classes) were assigned to microhabitat functional types. The results are essential for environmental flow assessments and allow 2‐ and 3‐dimensional habitat simulations in Mediterranean rivers; they are also useful to define critical habitats for the conservation of native fish populations.

Myxobolid parasites infecting the gills of the Iberian nase, Chondrostoma polylepis (Steindachner), in Galicia (NW Spain), with a description of Myxobolus gallaicus sp. nov.

Three species of myxobolid parasites were found infecting the gills of the Iberian nase, Chondrostoma polylepis, in the River Ulla (Galicia, NW Spain), Myxobolus leuciscini, M. impressus and M. gallaicus sp. nov., which is described herein. Myxobolus leuciscini locates in the intralamellar space and the plasmodium begins to develop in the endothelium of the capillaries of the secondary lamellae. Myxobolus impressus plasmodia are located in the interlamellar multilayered epithelium. Myxobolus gallaicus plasmodia are elongated and are located exclusively in the central venous sinus of the branchial filament, suggesting that they begin their development in branchial endothelial tissue. We also present data on spore size and morphology, plasmodium and pansporoblast characteristics and pathological effects of the three species in the host branchial tissues.

Microhabitat use by endangered Iberian cyprinids nase Iberochondrostoma almacai and chub Squalius aradensis

Over the last decade there has been a major rise in the number of attempts at fish conservation and management as a response to the widespread degradation of aquatic ecosystems. The assessments involved are rarely planned and executed with inputs from the species’ life history, particularly their microhabitat use over space and time. The seasonal and size related microhabitat use of two critically endangered cyprinids – the Iberian nase Iberochondrostoma almacai and Iberian chub Squalius aradensis – was examined at seven sites across four small catchments in southwest Portugal. Both species displayed nonrandom microhabitat use. In autumn, nase preferred more sheltered (>50% cover) habitats with small substrata (organic cover and silt) than in summer, while chub were found to occupy significantly fasterflowing habitats areas (>10 cm/s) with coarser substrata (>50 mm particle size) in the spring than in the rest of the year. Size-related analyses indicated that young-of-year (yoy) nase used coarser substrata (>5 mm particle size) and more exposed habitats (<50% cover) than adult nase. Adult chub, on the other hand, occupied coarser substrata (>50 mm particle size) and faster-flowing areas (>10 cm/s) than yoy and juveniles. Based on these findings, it was possible to assign the species to ecological guilds and to classify them as limnophilic (nase) and eurytopic and lithophilic (chub). Both species generally occupied distinct microhabitats, although resource-use overlap was significant in summer. During this season, overlap was found between yoy nase and chub, juvenile nase and juvenile/adult chub, and between adults of both species. The present study identified key factors in the species’ habitat requirements and helped develop management recommendations for river restoration that may have a wider application, particularly for other Mediterranean-type rivers.

Description of Myxobolus gayerae sp. n. and re-description of M. leuciscini infecting European chub from the Hungarian stretch of the river Danube

Myxobolus gayerae sp. n. and M. leuciscini González-Lanza & Alvarez-Pellitero, 1985 (Myxozoa: Myxobolidae) have been described and re-described from European chub Leuciscus cephalus L. from the Hungarian stretch of the river Danube. The ellipsoidal plasmodia of M. gayerae sp. n. were found in the mucosa of the intestinal wall, whereas the large, elongated plasmodia of M. leuciscini infected the afferent arteries of the gill filaments. The spores of M. gayerae sp. n. are relatively large, slightly oval and almost rectangular in shape. On the basis of spore morphology and 18S rDNA sequences, the most similar species was M. cycloides Gurley, 1893, but the 2 species differed in host and tissue tropism as well as in the size of the spores. The spores of M. leuciscini from L. cephalus, having no intercapsular appendix or occasionally a very small one, showed a high morphological similarity to spores collected from L. cephalus cabeda, Chondrostoma polylepis and Rutilus arcasi in Spain and described as M. leuciscini González-Lanza & Alvarez-Pellitero, 1985.