European Grayling Research Articles

Does the karst spring improve fish abiotic habitat in mountain streams?

Mountain streams constitute challenging habitat for many fish species due to rapid and variable flow, cool temperature, and limited food resources. Groundwaters recharge by karst spring may however mitigate harsh habit conditions of mountain streams providing niches for different fish species. This study aims to assess the suitability of mountain streams, replenished by karst springs, for various fish species like alpine bullhead, European grayling, brown and brook trout. The study was conducted in the Chochołowski Stream in the Western Tatra Mountains, Poland. The assessment of abiotic habitat is based on different characteristics of hydrological and thermal regimes as well as water chemical composition investigated between 01.09.2012 and 31.09.2014. The findings reveal that: 1) downstream variability of habitat abiotic conditions (such as water temperature, flow, water chemical composition) may affect the distribution of fish species, 2) karst springs contribute up to 100% of the stream’s recharge during periods of winter low flow, 3) karstic groundwater reduces the variability and amplitudes of stream water temperature and weaken the periodicity in water temperature associated with daily course of air temperature and solar radiation, 4) groundwaters prevent stream freezing in winter and moderate summer temperatures, 5) increasing mineralisation of water below the spring recharge may positively affect fish distribution. The findings underscore the importance of karst springs in modifying the abiotic conditions of fish habitat in mountain streams.

Can stocking with advanced European grayling fry strengthen its populations in the wild?

Can stocking with advanced European grayling fry strengthen its populations in the wild?

Європейський харіус (Thymallus thymallus Linnaeus, 1758). Тематична бібліографія

Purpose. Forming a thematic bibliographic list of English-language and Ukrainian-language publications, which highlight the issues of artificial breeding and cultivation of European grayling in Ukraine and abroad, the results of research into its population, ecological, genetic, physiological, biochemical, immunological and other characteristics. Methods. The complete and selective methods were applied in the process of the systematic search. The bibliographic core have been consisted of scientific publications in Ukrainian and English from the fund of the Institute of Fisheries NAAS Scientific Library, as well as resources available to its users. Results. There was composed the thematic list of publications with a total quantity of 200 sources covering the time interval from 1982 to 2024, and outlining issues regarding the reproduction of a representative of Salmonids — European grayling (Thymallus thymallus L.) as one of the most rare, valuable, and significant species in the ichthyofauna of Ukraine in terms of nature protection, research of its biological, morphological, ecological, genetic, physiological, biochemical and other features at various stages of ontogenesis and different living conditions. The literary sources were arranged in alphabetical order by author or title, and described according to DSTU 8302:2015 “Information and documentation. Bibliographic reference. General principles and rules of composition”, with the amendments (code UKND 01.140.40), as well as in accordance with the requirements of APA style — international standard of references. Practical value. The list may be useful for scientists, specialists, professors, and students whose area of interests includes research of rare and endangered species of fish, biological, population, genetic, ecological and other characteristics of Thymallinae, in particular in the context of their artificial reproduction. Key words: European grayling, endangered species of fish, breeding, pisciculture, genetic research, physiological and biochemical research, ecological research.

Metal concentrations in fish tissues from Kara, Bolshoi Patok, and Maly Patok River basins, Northeastern European Russia

Fish and fish tissue are effective bioindicators due to their sensitivity to pollution and are frequently used for assessing aquatic ecosystem health. Establishing baseline metal concentrations in freshwater fish tissues within aquatic ecosystems is important prior to establishing industrial activities to help determine potential future industrial impacts. Historically, North-Eastern European Russia has been an area with relatively low levels of industrial development and is still in pristine condition. In this region, the noise-to-background ratio for industrial contaminants may be disproportionately high. This study measured baseline metal concentrations in freshwater fish tissues collected from three study sites (the Bolshoi Patok, Maly Patok and Kara Rivers) in northeastern European Russia as bioindicators of overall aquatic ecosystem health. Seven fish species, namely, European Grayling, Arctic Char, Whitefish, Perch, Pike, Roach, and Peled, were studied over a three-year period between 2000 and 2003. The copper (Cu), lead (Pb), cadmium (Cd), and zinc (Zn) concentrations were analysed in fish tissue samples. Metal concentrations measured in fish tissues in this study were comparable to those measured at remote sites in Alaska, the United States and Slovenia. Despite the small variation between the sampling sites, the metal concentrations were relatively low and considered to be in pristine condition. Metal concentrations measured in fish tissues in this study represent baseline conditions, which will be important for comparison against monitoring programmes should the region experience future industrial development.

Fish stranding in relation to river bar morphology and baseflow magnitude: Combining field surveys and hydrodynamic–numerical modelling

AbstractHydropeaking mitigation based on down‐ramping thresholds is crucial to avoid stranding of fish and ensure sustainable hydropower production. However, the risk of stranding is influenced by several biotic and abiotic factors that interact with the ramping rate, including river morphology and baseflow magnitude. Also, at the river bar scale, the lateral or horizontal down‐ramping velocity may be of even greater importance than the vertical one as the prior integrates bar morphology. This study investigates the connection between ecologically relevant hydraulic parameters (vertical and lateral ramping velocity, dewatered river bar width) and the stranding of young‐of‐the‐year European grayling (Thymallus thymallus) due to down‐ramping, based on field observations of stranded fish at the hydropeaked Drava River in Austria combined with hydrodynamic–numerical modelling. We also examine the interplay between baseflow conditions and river topography in the dewatered areas. Stranding observations in spring and summer found a median rate of 90 individuals per 100 m, ranging from 50 to 500 fish per 100 m shoreline. Stranding rates were three times higher at night than during the day. Our data revealed a positive relationship between stranded fish and down‐ramping hydraulics, with higher intensity resulting in more stranded fish. This association was stronger for the lateral than the vertical ramping velocity, presumably because the former accounts for bar morphology, suggesting that the lateral dewatering velocity is a better indicator to assess fish stranding at the bar scale than the vertical velocity. We also found a negative relationship between the extent of the dewatered area and baseflow magnitude, indicating that the stranding risk is higher during down‐ramping at low flow conditions.

Validating morphometrics as a nonlethal tool to determine Arctic Grayling sex

AbstractObjectiveSome graylings Thymallus spp. possess an elongated dorsal fin and other morphological traits that can be sexually dimorphic, as demonstrated in the European Grayling T. thymallus. North American Arctic Grayling T. arcticus are assumed to follow these trends, but decisive evidence is lacking. This study aimed to determine whether sexually dimorphic characteristics, including posterior dorsal height, can be used to accurately predict the sex of Arctic Grayling in Interior Alaska.MethodsWe used computer imaging software to measure 22 morphometrics on 97 Arctic Grayling of known sex from streams in Interior Alaska, and we developed a set of binomial models to evaluate the validity of morphometrics as predictors of Arctic Grayling sex.ResultPosterior dorsal height was a reasonably accurate predictor of sex (~90% accurate at fork lengths ≥300 mm), although models containing additional morphometrics were more accurate (100% accuracy at fork lengths ≥250 mm).ConclusionThis study presents an affordable, noninvasive, and replicable method for nonlethal determination of Arctic Grayling sex by using digital images from the field, with potential application to other salmonids.

A habitat connectivity reality check for fish physical habitat model results and decision‐making for river restoration

Abstract Fish physical habitat models are a tool for guiding restoration efforts in lotic ecosystems, but often they overestimate restoration outcomes because currently they do not incorporate habitat connectivity. This persistent issue can, in extreme cases, result in little or no improvement to fish populations after the restoration, wasting valuable conservation resources. We present a case study where practitioners applied a fish habitat model for multiple life stages of gravel spawning fishes to a 52‐km stretch of the Iller River but did so at a microscale implementation by setting up a model based on cross sections with a maximum of 200 m distance from each other. This approach provided an opportunity to assess the connectivity of habitats for gravel spawning fishes, that is, European Grayling (Thymallus thymallus) and Common Nase (Chondrostoma nasus), integrating probabilities to find suitable habitats for all life‐history stages and seasonal movements. We used the assessed habitat estimates (availability of distinct habitat types within reaches defined by the 200 m cross sections) to calculate the minimum distance a fish would need to overcome to change from one habitat type into the other as it hypothetically ‘grew up’ from egg to full spawning adult. This approach can be interpreted as a life cycle habitat check as it considers all habitat types that are necessary to fulfil the life cycle of gravel spawning fishes including their size, distance and flow direction‐related orientation (e.g. larvae habitats only used when downstream of spawning areas). Our results show that the assumption of complete connectivity would require long movement distances for vulnerable life stages to find suitable habitat. This puts the high priority on the creation of migration corridors and passability of migration barriers in question. Without consideration of habitat types for all life stages of a species and their spatial context, restoration will not be successful. Shortly said: A perfect migration corridor does not necessarily provide habitat connectivity. We recommend the application of the habitat connectivity approach when predicting the effect of restoration measures and particularly setting the priority of measures for mitigation of fish migration.

The usage of probiotic microorganisms in production technology of European grayling fish stock

European grayling is a perspective object of a recreational fishing. In addition, the presence of this species in sufficient quantities in rivers has a positive influence on the formation of the recreational attractiveness of mountain regions, where tourism is one of the main sources of local communities existence. However, grayling stocks in the watercourses of Ukraine are significantly depleted nowadays, and populations are in a condition of lack, what has led to the inclusion of this species into the Red Book of Ukraine. Working out of biotechnologies of artificial reproduction of rare fish species in aquaculture conditions for the further reintroduction of the resulting offspring into natural water bodies takes an important place in the system of environmental protection measures to preserve biodiversity. After all, the reintroduction into nature of artificially obtained fish fry is one of the effective ways to restore the optimal number and structure of rare fish species natural populations, and this, in turn, will allow in the future to restore the limited exploitation of the stock of these fish species. One of the critical artificial fish reproduction technology links is the transfer of larvae to external nutrition. Namely on this stage the highest mortality rates are observed. The usage of live feeds as a starter fodder can significantly improve the situation. Forage organisms, in addition to having high nutritional value, can serve as delivering tools of various targeted products, including probiotics, to a fish larvae organism. The assessment of the usage of probiotic strain Lactobacillus casei IMV B-7280 feasibility is carried, and also the possibility of usage the culture Daphnia magna Straus, 1820 grown in the presence of trehalose lipids, within the technology of early feeding of the European grayling Thymallus thymallus (Linnaeus, 1758). It was shown that the larvae of the European grayling, which received investigated probiotic microorganisms strain, had 15% bigger weight on the final stages of feeding than the larvae of the control group. Introduction to the diet of grown-up grayling larvae of the culture Daphnia magna, previously received of common cultivation with microalgae Desmodesmus armatus (Chodat) E.H.Hegewald 2000 with addition of trehalose lipids, contributed to the reduction of larval mortality and the acceleration of their growth rate. Further improvement of proposed approaches of growing grayling fish planting material can be extrapolated to other fish species and in the future may be applicable in the process of growing rare fish species in conditions of farm aquaculture fish farms, what will allow them to be involved into environmental protection activities by placing appropriate orders. This, in its turn, will contribute to the stable development of communities in rural areas.

Historical and Current Distribution of the Brown Trout, European Grayling and Volga Nase in Small Rivers in the Republic of Tatarstan

Abstract We have studied the historical and current distribution of brown trout, European grayling, and Volga nase in the Republic of Tatarstan. The influence of environmental variables on the current distribution of these fish was assessed using regression methods. The probability of occurrence in small rivers of all three fish species is currently low, ranging from 2.8 to 5.3%. Each of the recorded environmental variables had statistically significant relationships with presence/absence of at least one fish species, but only two variables (elevation and human impact) significantly affected the probability of occurrence of all species in the study.

Fine ultrastructural features of germ cells and spermatozoa during spermatogenesis in the European grayling, Thymallus thymallus (Teleostei, Salmoniformes, Salmonidae).

This study aimed to examine the ultrastructure of spermatogenic stages and mature spermatozoa in the European grayling, Thymallus thymallus. The testes were examined microscopically with a transmission electron microscope to find out details of the structure and morphology of the grayling germ cells, spermatozoa and some somatic cells. The grayling testis has a tubular shape, with cysts or clusters of germ cells within seminiferous lobules. The spermatogenic cells, including spermatogonia, spermatocytes, and spermatids, can be found along seminiferous tubules. There are electron-dense bodies in germ cells from the primary spermatogonia to secondary spermatocyte stages. These undergo mitosis to reach the secondary spermatogonia stage, when they form primary and secondary spermatocytes. Spermatids undergo three different stages of differentiation during spermiogenesis, characterized by the level of chromatin condensation, elimination of cytoplasm, and the occurrence of the flagellum. The midpiece of spermatozoa is short and contains spherical or ovoid mitochondria. The sperm flagellum has an axoneme with nine doublets of peripheral microtubules and two central microtubules. The result of this study is valuable to be used as a standard reference for germ cell development, which is of great importance to get a clear insight into the process of grayling breeding practice.

Successful application of UV-irradiated rainbow trout (Oncorhynchus mykiss) spermatozoa to induce gynogenetic development of the European grayling (Thymallus thymallus)

In fish with the XX/XY sex determination system, the production of all-female offspring within one generation was achieved by gynogenesis. Successful induction of gynogenesis in the European grayling (Thymallus thymallus) (Salmonidae) included egg activation with UV-irradiated homologous (996 J/m2) and heterologous (rainbow trout) sperm (1370 J/m2) followed by exposure of the inseminated eggs to a high hydrostatic pressure (HHP) shock (9000 psi for 5 min) 20 min after their activation. The survival rates of the gynogenotic larvae at the swim-up stage exhibited a huge inter-clutch variability that ranged from 1.12 ± 0.53% to 14.15 ± 1.27% and from 0.96 ± 0.33% to 60.57 ± 1.85% when the eggs were activated by UV-irradiated homologous and heterologous sperm, respectively. Maternal inheritance was only confirmed in the gynogenotes that hatched from eggs inseminated by inactivated heterologous sperm, whereas an admixture of the paternal DNA was detected among screened individuals that originated from eggs activated by homologous sperm. All the examined gynogenotes produced using heterologous sperm were confirmed to be genetically females. In the case of fish with an admixture of the paternal DNA, male genotypes and phenotypes were observed. One of the genetic males had well developed testes. Differences in the ratio of deformed larvae that hatched from eggs activated by UV-irradiated homologous and heterologous sperm were nonsignificant. Based on the obtained results, it has to be stated that the activation of grayling eggs with UV-irradiated rainbow trout sperm followed by HHP shock is a reliable and fast method for the production of all-female grayling stocks.

Reproduction parameters of hatchery reared grayling (Thymallus thymallus) females

European grayling (Thymallus thymallus) is an endangered salmonid fish species and its populations have decreased considerably in European waters in recent decades. One of the conservation measures applied to grayling is stocking with hatchery-reared fish. To advance the knowledge of grayling reproduction in the hatchery, husbandry data were systematically collected in the period from 2006 to 2015 during grayling spawning seasons and analyzed to quantify grayling female reproductive parameters such as fecundity, egg size, and embryo survival to the eyed egg stage. Data was collected for first time spawners (3 years old) and repeat spawners reared in the hatchery. Statistically significant differences were found for the number of eggs between first time spawners, producing on average 3600 eggs, and repeat spawners, producing on average 8000 eggs. Absolute fecundity was positively correlated to grayling female total length and weight for both first time and repeat spawners. However, relative fecundity did not correlate with these parameters. A positive correlation was observed between female total length and mean egg weight for repeat spawners, while the correlation was negative for first time spawners. Heavier eggs tended to have a higher rate of survival until the eyed egg stage, though the correlation was stronger for first time spawners than for repeat spawners. Due to the higher reproductive success of repeat spawners, it could be concluded that larger and older grayling females should be included in hatchery reproduction.

Assessment of the Population of the European Grayling under Limited Data

The state of populations of European grayling Thymallus thymallus (Linnaeus, 1758) has been assessed and compared in two Ural tributaries of the Pechora River. The grayling inhabiting the Shchugor River (the territory of Yugyd Va National Park) has been satisfactorily preserved with minimal shifts in population characteristics. In the Bolshaya Synya River, protected only at the river source, the grayling population decreased mostly by the fish of the maximum age (up to 7+), the share of repeatedly spawning individuals has decreased as well (4.0–4.8%), and the overall mortality rate has increased. Deterioration of the grayling population in the Bolshaya Synya River was due to intensive illegal fishing. Under limited initial data, using a set of traditional indicators appeared a more universal assessment approach, while the length-based indicators (LBIs) method has only limited application.

Effects of cold and warm thermopeaking on drift and stranding of juvenile European grayling (Thymallus thymallus)

AbstractIntermittent water releases from hydropower plants, called hydropeaking, negatively affect river biota. The impacts mainly depend on hydrological alterations, but changes in physical habitat conditions are suspected to be co‐responsible. For example, hydropeaking accompanied by a sudden change of water temperature in the downstream river—called thermopeaking—is also presumed to impair aquatic ecosystems. Still, knowledge about these thermopeaking impacts on aquatic species and life‐stages is limited. We performed flume experiments under semi‐natural conditions to fill this knowledge gap, simulating single hydropeaking events with a change in water temperature. As response parameters, we quantified the drift and stranding of early life‐stages of European grayling (Thymallus thymallus L.), a key fish species of Alpine hydropeaking rivers. Hydropeaking events with a decrease in water temperature (“cold thermopeaking”) led to significantly higher downstream drift (mean = 51%) than events with increasing water temperature (“warm thermopeaking”, mean = 27%). Moreover, during cold thermopeaking, a comparably high fish drift was recorded up to 45 min after the start of peak flows. In contrast, drift rates quickly decreased after 15 min during warm thermopeaking. Remarkably, the spatial distribution of downstream drift along gravel bars during cold thermopeaking showed the opposite pattern compared to those triggered by warm thermopeaking events indicating different behavioral responses. Furthermore, the stranding rates of the cold thermopeaking trials were twice as high (mean = 31%) as those of the warm thermopeaking experiments (mean = 14%). The outcomes present vital information for improving mitigation measures and adapting environmental guidelines.

Density-dependence and environmental variability have stage-specific influences on European grayling growth

Fish somatic growth is indeterminate and can be influenced by a range of abiotic and biotic variables. With climate change forecast to increase the frequency of warming and unusual discharge events, it is thus important to understand how these variables currently influence somatic growth and how that might differ for specific age-classes and/ or life stages. Here, we used a 17-year dataset from a chalk stream in southern England to identify the abiotic and biotic influences on the growth of juvenile, sub-adult and adult life stages of European grayling (Thymallus thymallus), a cold-water riverine salmonid. The results revealed that interannual variations in grayling growth were well described by annual- and site-specific abiotic and biotic explanatory variables. We found divergent responses between life stages to increased temperature and unusual discharge during the main growth period with, for example, elevated temperatures related to increased juvenile growth but reduced sub-adult growth, and high discharge events related to increased sub-adult growth yet reduced juvenile growth. Conversely, stage-specific grayling abundance negatively influenced growth at each life stage, though only juvenile growth was impacted by the abundance of a competitor species, brown trout (Salmo trutta). These results emphasise the merits of testing a wide range of environmental and biological explanatory variables on fish growth, and across life stages. They also reveal the importance of maintaining high habitat heterogeneity in rivers to ensure all life stages can reduce their competitive interactions and have access to adequate flow and thermal refugia during periods of elevated environmental stress.

Water as a Source of Indoor Air Contamination with Potentially Pathogenic Aeromonas hydrophila in Aquaculture.

Human activities influence the presence of potentially pathogenic bacteria in indoor air. The aim of this study was to determine the effect of the experimental rearing of European grayling and European perch in a recirculating aquaculture system on the contamination of indoor air with potentially pathogenic Aeromonas hydrophila (PPAH) and the resulting health risks to humans. The PPAH counts, their resistance to seven antibiotics, and the multiple antibiotic resistance (MAR) index were determined in samples of indoor air and water from rearing tanks. The PPAH counts were highest in the laboratory bioaerosol where two fish species were reared. The calculated indoor/outdoor ratio (I/O > 1) demonstrated that tank water was the internal source of PPAH emissions. The unconstrained PCA revealed strong positive relationships (p ≤ 0.05) between the PPAH counts in the indoor air and water samples. Most of the PPAH strains isolated from laboratory air were resistant to tetracycline, cefotaxime, and erythromycin, and 26–82% of the isolates exhibited multiple drug resistance. The values of the MAR index were similar in samples of laboratory air and water (0.23–0.34 and 0.24–0.36, respectively). Agglomerative clustering revealed two clusters of strains isolated from laboratory air and tank water. The results of this study indicate that aquaculture can be a source of indoor air contamination with PPAH.

Application of high hydrostatic pressure (HHP) shock to induce triploid development in the European grayling (Thymallus thymallus L.)

Use of parental individuals from allochthonous lineages to produce stocking specimens resulted in genetic contamination of many local European grayling (Thymallus thymallus) populations. Stocking programs including triploid individuals that are not able to reproduce with stocks located in natural habitats due to being reproductively sterile could contribute to populations of the European grayling and prevent regional lineages from the genetic pollution. The main goal of the present research, therefore, was to provide conditions for triploidization of the European grayling and examine gonads of triploid individuals. High Hydrostatic Pressure (HHP) shock (9000 psi/5 min.) applied to activated and incubated grayling eggs at 10 °C between the 17 min. 30 sec. and 20 minute timepoints subsequent to the time of insemination resulted in inhibition of the second polar body release and triploidization. Histological analysis confirmed that all 1-yr-old cytogenetically confirmed triploids had gonadal tissues indicative of sterility with the gonads being composed of connective tissue including fibroblasts, adipocytes and degenerated epithelial structures without there being any differentiated germ cells detected. There were no differences in the body length and Fulton’s condition factor between 1 year old diploid and triploid grayling, however, the average body weight was markedly less in triploid than diploid specimens. Although, 1-yr-old triploid European female and male graylings did not have fully developed gonads, before these triploid specimens are deemed safe, as a result of being reproductively sterile for stocking in natural grayling habitats, there needs to be further examination of the 2- and 3-year-old triploid specimens.

Doubts about the validity of the species name Hipparchia hermione (Linnaeus, 1764), it being associated with the two species Hipparchia alcyone ([Denis & Schiffermüller], 1775) and Hipparchia genava (Fruhstorfer, 1908) following the designation of a lectotype by Kudrna (1977) (Lepidoptera: Nymphalidae, Satyrinae) - First part -

In 1977, Otakar Kudrna (*1939-†2021, obituary see Balletto and Leigheb, 2021) published his “Revision of the Genus Hipparchia”, where he classified all the known species and forms of this genus according to characters of wings, androconia, male genital armatures and further subjective criteria. Until today, Kudrna’s study is considered as the guideline of systematics of the genus Hipparchia. He selected there a lectotype specimen of a Rock Grayling male in the Linnaean collection. “Hipparchia hermione Linnaeus, 1764” is therefore, at the moment, the technically correct name to identify the species. The “International Commission of Zoological Nomenclature” (ICZN) has nothing to add at this point; it only comments on cases submitted to it in the Bulletin of Zoological Nomenclature. Within the meaning of the present study and in accordance with Verity (1913), this damaged specimen without abdomen represents the same species as Ignaz Schiffermüller – allegedly the only author of the Vienna directory (see Kudrna and B., 2005, p. 5) – has described under H. alcyone from the Vienna region by referring to a coloured copper engraving published by Rösel von Rosenhof (1755). Kudrna’s “Revision” became the starting point of an extended scientific research activity during my free time containing, as a matter of priority, the examination of problem cases of systematics by checking the preimaginal characters of many rearing series from different sites. It turned out that a number of classifications proposed by Kudrna (1977) had to be reassessed as soon as characters of the pre-imaginal stages were available. The most complex case I have verified concerned the third European Grayling species which Leraut (1990) introduced under the name of Hipparchia genava (Fruhstorfer, 1908). Kudrna (1977) failed to separate this species from H. alcyone (D. & S., 1775). Throughout his life, he never agreed with Leraut’s opinion. In recent years, Kudrna had hoped that genetic examinations would make redundant every rearing attempt by amateur lepidopterists and furnish the proof that his opinion was the correct one. Since he never undertook any rearing experiments, his systematics were based only on prepared imagines being housed in museum collections. He saw himself as a person with the competency to decide within a few minutes upon complex questions of taxonomy and ignored completely the assessments of others. For verifying the effective rank of H. genava, I had to examine also the two most closely related species: Hipparchia fagi and H. alcyone by rearing them all ex ovo with material from several widely spaced sites. Already on finalising my rearing work of this group, it became apparent that Leraut (1990) had been on the absolutely right path by accepting a third Grayling species, within this group. For the first time, I published the results of my rearing attempts between 2002 and 2006 in several articles in the quarterly bulletin Linneana Belgica and I readily provided information on this case to interested colleagues. Over time only, I realized that the Rock Grayling I knew from the volume on butterflies (Diurna) by Forster and Wohlfahrt (1955) as from the guides by Higgins and Riley (1970-84) under the name of H. alcyone had become H. hermione, because of the lectotype designation by Kudrna (1977). A stony path was in front of me to substantiate the factual correctness of the view taken by Leraut (1990). Complex clarifications by Peter Russell furnished well-founded arguments on the complex scientific issue why the use of the name “hermione Linnaeus, 1764” should be rejected for the Rock Grayling previously known as H. alcyone.

Modelling fish habitat influenced by sediment flushing operations from an Alpine reservoir

The periodic removal of deposited sediment in Alpine artificial reservoirs can be carried out through the flushing technique, in which the bottom outlets of the dam are opened to let water flow through the gates, eroding, re-suspending and transporting the sediment downstream. However, this reservoir sediment management strategy normally generates marked variation both in the flow rate and in the Suspended Sediment Concentration (SSC) in the river reaches downstream of the dam and may produce negative effects on the riverine ecosystems and biotic communities, especially on fish. In particular, the alteration of river hydraulic parameters (i.e., water depth and flow velocity) combined with excessive turbidity values (i.e., high SSC values) may lead to a possible worsening of habitat suitability for fish, increasing animal stress. The existing known literature provides useful tools to model the effects of the varied river hydraulic characteristics and the increased fine sediment load, but separately. Due to the simultaneous increase of river flow and SSC, it would instead be advisable to combine these two parameters to obtain a comprehensive and representative fish habitat modelling during flushing events. Therefore, the present work aims to propose an innovative methodology for the European grayling (Thymallus thymallus, L. 1758) habitat modelling during sediment removal from an artificial reservoir, in order to minimize the ecological effects while optimizing reservoir sediment management. With the aim of generalizing our results, we considered two river reaches with different morphologies located in South Tyrol (NE Italy), respectively 0.8 km and 18 km downstream the Rio di Pusteria reservoir, two life stages of our model organism, grayling, a typical rheophilic freshwater fish species inhabiting the studied river, and three possible volumes of flushed sediment. Results showed that habitat suitability for spawning and juvenile grayling tended to decrease with increasing flow and SSC for each of the fish life stage considered. However, interestingly, it was preferable to increase the water outflow from the dam to reduce the flushing duration when considering high volumes of trapped sediment.

Ecohydraulic tools for aquatic fauna habitat and population status assessment, analysis and monitoring aimed at promoting integrated river management

The ecohydraulic modeling framework in ecological systems includes hydro-morphodynamic, habitat, and population models. In this paper, we proposed an ecohydraulic modeling framework that combines numerical methods and ecological theories to explore the dynamics and interplay between fluvial processes in rivers and the quality of physical habitat and density distribution for fish. The practicality of applying the developed system to ecohydraulics modeling was explored through three case studies and compared with as well as validated using observed data. On the basis of the calculated results, the model system was proven to be efficient in describing population dynamics of the European grayling (Thymallus thymallus. L.) in the Aare River in Switzerland. Satisfactory predictions of the long-term population evolution of the rainbow trout (Oncorhynchus mykiss), brown trout (Salmo trutta) and flannelmouth sucker (Catostomus latipinnis) in the Colorado River in the United States (US) were obtained. Furthermore, the effects of Da-Wei Power Plant construction on the Jiao-Mu River in China on the schizothorax (Schizothorax prenanti) and schizothorax (Racoma) fish species were investigated. The efficiency of fish stocking strategies was evaluated and optimal fish stocking numbers were proposed. The resulting ecohydraulic modeling framework provided very promising results, which highlighted the fundamental role of the temporal variability of hydro-morphological parameters in structuring populations of fish species. Using the ecohydraulic modeling framework to simulate population trends in anticipation of any changes in water management can provide decision-makers with valuable prediction results.