Abramis Research Articles

CURRENT STATE OF POPULATIONS OF THE MAIN COMMERCIAL FISH SPECIES OF THE SMALL ARAL SEA

The Aral Sea was one of the main commercial basins until the 80s of the last century. However, intensive water management activities aimed at regulating the upper reaches of the Syrdarya and Amudarya rivers, which were the main sources of water supply in the Aral Sea, led to a decrease in the water level and the sea was initially divided into two reservoirs: Small and Large. As a result, huge damage was caused to the fishing industry of the region. And only after more than 20 years, a decision was made to restore the Aral Sea, by building a dam, in order to block the channel connecting the Small Aral with the Big Sea. In 2005, the construction of the Kokaral separation dam was completed. The basis of the fishery is: bream (Abramis brama), zander (Sander lucioperca), pike (Esox lucius), asp (Aspius aspius), carp (Cуprinus caspio)

Comparative Analysis of the Feeding Spectrum of Bream Abramis brama L. (Cyprinidae, Pisces) in Different Areas of the Rybinsk Reservoir

Comparative Analysis of the Feeding Spectrum of Bream Abramis brama L. (Cyprinidae, Pisces) in Different Areas of the Rybinsk Reservoir

Susceptibility to Oxidation of Selected Freshwater Fish Species Lipids as a Potential Source of Fish Oil in Dietary Supplements.

Polyunsaturated fatty acids from the omega 3 family are more and more often supplied to the diet in the form of supplements. The aim of the study was to characterize the lipid fractions of predatory freshwater fish, i.e., pike (Esox lucius L.), perch (Perca fluviatilis L.), and pike perch (Sander lucioperca L.), and omnivorous fish, i.e., bream (Abramis brama L.) and roach (Rutilus rutilus L.). Their technological usefulness in terms of the source of fish oil was determined, depending on the rate and degree of their oxidative changes. UV radiation (photooxidation test) was used as a factor accelerating lipid oxidation. Research has shown that selected species of freshwater fish are characterized by high lipid oxidative stability, due to the availability and speed of delivery to the processing plant. The initial level of lipid oxidation of their meat, expressed by the TOTOX index, in any species did not exceed the value of 7, while the acceptable value was 26. The oil obtained from the meat of omnivorous fish after the photooxidation process was characterized by significantly better oxidative stability compared to the oil from the meat of predatory fish. The oxidation resistance of omnivorous fish oil was shown to be higher than that of predatory fish.

European fish-based assessment reveals high diversity of systems for determining ecological status of lakes

Triggered by the adoption of the Water Framework Directive, a variety of fish-based systems were developed throughout Europe to assess the ecological status of lakes. This paper provides a comprehensive overview of all existing systems and summarizes sampling methods, fish community traits (metrics) and the relevant anthropogenic pressures assessed by them. Twenty-one European countries developed fish-based assessment systems. Three countries each developed two distinct systems to approach different ecoregions, either to use different data, or to assess different lake types leading to a total number of 24 systems.The most common approach for the setting of reference conditions, used in seventeen systems, was the utilisation of fish communities in comparably undisturbed natural lakes as reference. Eleven used expert judgment, nine historical data and eight modelled relationships. Fourteen systems combined at least two approaches.The most common fish sampling method was a standardized fishing procedure with multimesh-gillnets. Many countries applied combinations of fishing methods, e.g. non-standard gillnets, fyke nets and electrofishing.Altogether 177 metrics were used for index development and each system combined 2–13 metrics. The most common ones were total standardized catches of number and biomass, relative abundance of Perca fluviatilis, Rutilus rutilus, and Abramis brama, feeding preferences, sensitive species, and non-natives. The pressure-response-relationships for these metrics were supported with both correlations established during system development and scientific publications. However, the metrics and their combinations were highly diverse and no metric was applied universally.Our analysis reveals that most fish-based assessment systems address multiple pressures (eutrophication, hydromorphological alterations, fishery pressure and occurrence of non-natives), whilst few are pressure-specific, tackling only eutrophication or acidification. We argue that the value of fish-based systems for lakes lies in their capacity to capture the effect of many different pressures and their interactions which is lacking for most assessment systems based on other biota.

SPECIES COMPOSITION AND RELATIVE POPULATION SIZE OF FISHES IN THE OSTER RIVER (THE DESNA RIVER BASIN): 50 YEARS ANALYSIS

Inroduction. Changes in the species composition and population size of freshwater fihes are determined by deformations of the habitat in Ukraine and are characterized by a pronounced negative dynamics. Deformation of ichthyofauna is caused by extinction of a number of aboriginal fihes and emergence of alien species.Aim. To establish the current species composition and relative population size of fih species in the Oster River and the dynamics of these characteristics over a 50-yearlong period in the context of negative transformations of the ichthyofauna of the rivers of Ukraine.Results. Comparative study of the species composition and relative population size of fih species in the fih catches by small-river fihing gear in the Oster river was conducted during the period since 1971-72 till 2019. During this time considerable changes in species composition took place. The following species disappeared from the catches: Leuciscus leuciscus, Leuciscus idus, Chondrostoma nasus, Carassius carassius, Blicca bojerkna and Neogobius flviatilis, they were replaced by three invasion species (Percottus glenni, Pseudorasbora parva, Proterorhinus marmoratus). The changes in the dominant species took place, thus, in the Oster ichthyocene the species with the short life cycle started to prevail, the share of invasion species increased from 1.4 to 37%, and the share of initial marine fih among them is very low. The comparison with the river systems of the Stugna and the Lower Dnipro represents the fact that the mentioned negative tendencies are common for the whole Dnipro system, however the situation in the Lower Dnipro must be considered less critical than in the Oster and the Stugna rivers. The fact that the catches of industrial fih decreased more than 10 times in the Desna river during this period of time gives the reason to consider that the dramatic reduction of the absolute number of their populations occurred in the Oster river as well. That is why even relatively safe species (Abramis brama, Rutilus ritilus, Scardinius erythrophthalmus, Esox lucius, Perca flviatilis, Alburnus alburnus, Squalius cephalus) are in critical situation in this transformed river system.Сonclusions. In the ichthyocene of the Oster River over a 50-year period there have been signifiant changes in species composition, relative and absolute population numbers associated with the extinction and reduction of population sizes of rheophilic species and fih that are adapted to life in the flodplain. The modern Oster River is dominated by invasive and short-cycle species. The obtained tendencies in the dynamics of the ichthyofauna of the Oster River are similar to the nature of changes in other river systems of Ukraine, although they occur at a faster pace, which is characteristic of the smallest plain rivers.

Temporal variation of biomarkers in common bream Abramis brama (L., 1758) exposed to untreated municipal wastewater in the Danube River in Belgrade, Serbia.

This study was conducted on the Danube River locality Višnjica, exposed to the discharge of the largest wastewater collector in Serbia's capital, Belgrade. Concentrations of metals and metalloids (Al, Fe, Cr, As, Sr, Mn, Cd, Zn, Mo, Cu, Li, Ni, B, Co, Pb, and Ba) and histopathological alterations were investigated in different tissues of common bream during one representative month of each season in 2014. This is the first study in which these two biomarkers were assessed parallelly in common bream. The highest concentrations of examined elements were noticed in gills and the lowest in muscle. Statistically significant differences in element concentrations between different seasons were noticed only in gills for Al, Cu, and Fe. Concentrations of As and Pb in fish muscle were below the maximum acceptable concentrations (MAC). The histopathological index (HI) of the liver showed higher values in comparison to the HI of the gills. Histopathological index of the gills had a significantly higher score in November in comparison to August. The liver HI had the highest score in April, and the lowest in August, while the total histopathological index had the highest score in November, and the lowest in August, both without significant differences between the months. This study endorses gills and liver as reliable organs for studying accumulation and histopathology as biomarkers of environmental changes. A faster reaction of the gills was confirmed since seasonal variations of both biomarkers were observed in this organ. Common bream proved as a good indicator of the state of organisms in polluted environments.

MORPHOLOGY OF ADULTS AND IMMATURES OF THE ACANTHOCEPHALAN, POMPHORHYNCHUS FUHAIENSIS YUE, 1998 (ACANTHOCEPHALA: POMPHORHYNCHIDAE) FROM CYPRINID FISH IN NORTHWEST CHINA.

Adult specimens of Pomphorhynchus fuhaiensis were identified from common carp (Cyprinus carpio L.) in Ulungur Lake of northwest China, and acanthors, acanthellae, cystacanths dissected from Gammarus lacustris in a small tributary of Ulungur River for the first time. The acanthocephalans were also found in crucian carp (Carassius carassius L.), tench (Tinca tinca L.), oriental bream (Abramis brama orientalis Berg), and ide (Leuciscus idus L.) in the lake. This species is distinguished from other species in Pomphorhynchus by its large, spherical bulb and very long neck as well as by a cylindrical proboscis armed with 15-17 longitudinal rows of 9-12 hooks each. The anterior proboscis hooks are almost uniform in size and shape, the sixth hook in a short row and the seventh hook in long row decrease abruptly in size posteriorly with the last end hook being a little larger than the prebasal hook, and in a ring; posterior proboscis hooks much more widely spaced. Furthermore, the lemnisci are claviform. The mean neck:trunk ratio is about 0.5, which is larger than most other species in Pomphorhynchus. Females are larger than males. In males, the testes are in one-third to one-half of the trunk, equal, ovoid-spheroid, usually contiguous, and small relative to the body size, and there are 6 ovoid cement glands. Pomphorhynchus fuhaiensis is similar to Pomphorhynchus laevis but can be distinguished by the number of longitudinal rows of hooks. Pomphorhynchus laevis is armed with 18-20 longitudinal rows of 11-13 hooks, P. fuhaiensis is armed with 15-17 longitudinal rows of 9-12 hooks.

ИХТИОФАУНА НЕКОТОРЫХ ВОДОЁМОВ МЕСТНОГО ЗНАЧЕНИЯ АКСУСКОГО РАЙОНА, ПАВЛОДАРСКОЙ ОБЛАСТИ

In 2020, research works were carried out on seven reservoirs of local significance in Aksu district, Pavlodar region. These are Lake Komendant, Lake Krasnoe, Lake Lesnoe, Lake Topalevoe, Lake Kara Murza, Lake Baltazhar and the Karasu Channel. In these reservoirs, the ichthyological composition was studied, such fish species as pike (Esox lucius L., 1758), silver carp (C. gibelio (Bloch, 1782)), golden carp (Carassius carassius (L., 1758)), rotan (Perccottus glenii Dybowski), tench (Tinca tinca (L., 1758)), perch (Perca fluviatilis L. ,1758), roach (Rutilus rutilus (L., 1758)), carp (Cyprinus carpio L.,1758), and bream (Abramis brama (L., 1758)). The species of fish included in the Red Book of the Republic of Kazakhstan, as well as rare or endangered, are not marked in the research catches of the studied reservoirs.

Long-term dynamics of radionuclide contamination formation in the industrial іchthyofauna of the Kaniv Reservoir

The aim the study is to determine the temporal parameters of the long-lived radionuclides specific activity decrease in the commercial fish species of the Kaniv Reservoir for the period 1987–2021. Rutilus rutilus, Scardinius erythrophthalmus, Blissa bjoerkna, Abramis brama, Pelecus cultratus (peaceful species) and Esox lucius, Stizostedion lucioperca (carnivorous species) were selected in the middle and lower parts of the reservoir in January 2021 to determine the current levels of radioactive contamination in the representatives of the commercial ichthyofauna of the Kaniv Reservoir. The specific activity of 90Sr and 137Cs was determined in the entire body of fish by conventional radiochemical and gamma-spectrometric methods. The analysis of the dynamic characteristics of the radionuclides content in the representatives of the reservoir ichthyofauna was carried out on the basis of the results of studies of 90Sr and 137Cs content in fish during 1987–2012 and their specific activity in the body in 2021. In 2021, the average specific activity of 90Sr in fish was 0.6–1.6 Bq/kg, 137Cs - 2.4–13.2 Bq/kg. According to the results of previous studies, the average specific content of 90Sr in the fish of the Kaniv Reservoir decreased by approximately 6.5 times - from 60 ± 30 to 9 ± 3 Bq / kg during 1987-1993, and by 2003 it decreased by another 5 times up to 1.8 ± 0.8 Bq / kg and did not exceed the values recorded in freshwater fish in Ukraine before the Chernobyl accident in 1979–1985. Consequently, during the period of 2003–2021 the levels of 90Sr content in fish from the Kaniv Reservoir remained virtually unchanged. Based on the data on 137Cs accumulation in various feeding types fish in the Kaniv Reservoir, time parameters describing a decrease in the element specific activity were determined. During 1987–2021 the rate of decrease in 137Cs content in peaceful and predatory fish did not differ significantly and amounted to 0.10 ± 0.01 year-1, the period of effective half-decrease was 6.7 ± 0.7 years. Analysis of long-term data made it possible to distinguish 2 periods during which the specific activity of 137Cs in the fish organism decreased at different rates. In 1987-2004, 137Cs content levels in peaceful fish decreased from 70 ± 22 to 6.1 ± 2.2 Bq/kg, in carnivorous species - from 202 ± 41 to 19.8 ± 7.6 B/ kg, i.e. approximately by 10–11 times, which corresponds to a half-decrease of about 6 years. In 2004–2021 the element content in peaceful fish decreased to 2.9 ± 0.7 Bq/kg, in predatory fish - to 7.3 ± 4.1 Bq/kg, that is, by another 2–3 times, which corresponds to a half-decrease of 12 ± 3 years. Thus, it was found that the rate of decrease in 137Cs specific activity in fish slows down over time. The obtained parameters will make it possible to predict with a high degree of accuracy the dynamics of the radionuclide contamination formation in ichthyofauna in the event of artificial radionuclides entering aquatic ecosystems as a result of emergency situations. Key words: Kaniv Reservoir, fish, radionuclides, longterm dynamics, rate of decrease.

Movements of common bream Abramis brama in a highly connected, lowland wetland reveal sub‐populations with diverse migration strategies

Abstract Studies suggest the migratory behaviours of potamodromous fishes can be highly variable in barrier‐free systems, where differing movement types enable populations to exploit a wide range of food and space resources. This intra‐population diversity in spatial and temporal resource use is important to our ecological understanding of fish distribution patterns and population structure. Despite this, freshwater ecosystems are increasingly characterised by high levels of fragmentation and degradation that restrict mobile fauna, and limit opportunities to study natural, unconstrained movement behaviour. Common bream Abramis brama (bream) is a potentially strong model species for testing the importance of diverse migration patterns in lowland rivers, but existing studies have been largely restricted to spatially confined and/or anthropogenically modified systems. This study's principal focus was to examine the diversity of bream movement behaviour in a highly connected, lowland system using passive acoustic telemetry, which provided continuous, multi‐year data on the movements of 181 bream across a tidally influenced, lowland wetland in eastern England (c. 60 km of continuous river length plus numerous interconnected shallow lakes and dykes). Tracked bream were grouped according to their initial location and timing of tagging. Bream migratory behaviours varied considerably between tagging groups, but with greater consistency within groups. There was little mixing of groups outside of spawning periods, with season and tidal phase being significant predictors of movement. Rates of movement and swimming speeds were highest in spring, with movements also generally occurring in the direction of tidal flows. For fish sampled just prior to spawning, there was considerable diversity in their post‐spawning behaviour, with some remaining in the immediate vicinity of the sampling location and others that moved to areas c. 25 km away. These spatially discrete patterns remained until the following spawning period. These results suggest that this lowland fish population is comprised of several distinct, semi‐independent subpopulations that only share space resources in their spawning period. This indicates the importance of connectivity in lowland freshwater systems for enabling and maintaining high phenotypic diversity in the movement behaviours of potamodromous fishes.

Acoustic telemetry reveals strong spatial preferences and mixing during successive spawning periods in a partially migratory common bream population

Partial migration, whereby a population comprises multiple behavioural phenotypes that each have varying tendencies to migrate, is common among many animals. Determining the mechanisms by which these phenotypes are maintained is important for understanding their roles in population structure and stability. The aim here was to test for the temporal and spatial consistency of migratory phenotypes in a common bream Abramis brama (‘bream’) population, and then determine their social preferences and extent of mixing across three successive annual spawning periods. The study applied passive acoustic telemetry to track the movements of bream in the River Bure system of the Norfolk Broads, a lowland wetland comprising highly connected riverine and lacustrine habitats. Analyses revealed that individual migratory phenotype was highly consistent across the 3 years, but this was not predicted by fish sex or length at tagging. During the annual spawning periods, network analyses identified off-channel areas visited by both resident and migrant fish that, in non-spawning periods, were relatively independent in their space use. Within these sites, the co-occurrence of bream was non-random, with individuals forming more preferred associations than expected by chance. These associations were not strongly predicted by similarity in fish length, sex or behavioural phenotype, indicating that the resident and migrant phenotypes mixed during their annual spawning periods. The results suggested these different phenotypes, with spatially distinct resource use in non-spawning periods, comprised a single population, with this having important implications for the management of this wetland resource.

SOME INFORMATION ON THE CARP FISH SPECIES FEEDING

The article presents the results of studies of feeding characteristics of such cyprinid fish species as the roach Rutilus rutilus caspius (Jakowlev, 1870) and the bream Abramis brama (Linnaeus, 1758) in various parts of the Daghestan coast of the Caspian Sea. The material was sampled along the entire Daghestan coast of the Caspian Sea, from the Kizlyar Bay to the mouth of the Samur river, in different biological seasons in the period of 2017–2018.

Impact of habitation conditions on metabolism in the muscles, liver, and gonads of different sex and age groups of bream

Impact of the factors of the aquatic environment is an inevitable aspect of the life of fish as poikilothermic animals and provokes responses in their organisms. The study focused on determining peculiarities in the composition of the metabolic products in the tissues of different age and sex groups of common bream Abramis brama (L.) depending on the living conditions in the water reservoirs of the Upper Volga. The fish were captured in the fattening period in summer and autumn, measured, weighed, identifying sex, maturity stage of the gonads and age. In the muscles, liver and gonads of bream, we analyzed the contents of water, dry matter, lipids, protein, ash and carbohydrates using the standard techniques. The contents of biochemical components in the organism of bream were to a higher degree determined by the peculiarities of the living conditions rather than sex and age of the individuals. In the muscles and liver of bream living in the conditions of increased water temperature and low concentration of oxygen, the concentrations of protein and ash were lower. In the same tissues of bream from the water bodies with high concentrations of pollutants in the water and benthic deposits, we found increased fat content. The muscles of male bream contained less protein and more carbohydrates than females and juvenile individuals, and the muscles of juveniles had less fat. The environmental factors had greater influence on the content of the metabolic products in the liver of bream than sex, and only females had higher ash content than males. The testes had more fat and less protein than the ovaries. During the transition of the gonads from maturity stage II to III, the contents of dry matter and lipids in them decreased. We determined that the environmental factors have stronger impact on biochemical parameters in the tissues of bream than age, because we found no general age patterns in the dynamics of biochemical components, except the liver, in which the highest content of organic compounds was found in individuals aged 6 to 10 years. Water heated by the Hydro Power Plant positively influenced the young bream, as indicated by higher content of metabolic products in individuals aged 5+ than older groups and bream from the surveyed water bodies. Monitoring of the physiological condition of bream focusing on the contents of metabolic products in the tissues may provide necessary data for successful regulation of bream populations in the water reservoirs of the Upper Volga.

Dual‐isotope isoscapes for predicting the scale of fish movements in lowland rivers

AbstractAssessments of patterns of animal movements are important for understanding their spatial ecology. Geostatistical models of stable isotope (SI) landscapes (isoscapes) provide a complementary tool to telemetry for assessing and predicting animal movements, but are rarely applied to riverine species. Often single‐isotope gradients in freshwater environments are insufficiently variable to provide high isoscape resolution at relatively fine spatial scales. This is potentially overcome using dual‐isotope assignment procedures, and thus, the aim here was to apply single (δ13C) and dual (δ13C and δ15N) isoscapes to assigning riverine fish to origin and predicting their movements. Using the River Bure, England, as the study system, the foraging locations of a small‐bodied lowland river fish (roach Rutilus rutilus) of low vagility were predicted using their SI data and those of a common prey item (amphipods). These foraging locations were then compared to their capture locations, with the distance between these being their predicted displacement distance. The results indicated significant enrichment of δ13C and δ15N with distance downstream in roach fin tissue and amphipods; roach bivariate isotopic niches were spatially variable, with no niche overlap between upstream and downstream river reaches. Furthermore, the dual‐isoscape assignment procedure resulted in the lowest predicted displacement distances for roach, therefore enhancing model performance. The dual‐isoscape approach was then applied to determining the predicted displacement distance of individual common bream Abramis brama, a larger, more vagile species, with these data then compared against the subsequent spatial extent of their movements recorded by acoustic telemetry. When using a high probability density threshold for isotope assignment, the predicted displacement distance of common bream was a significant predictor of the spatial extent of their subsequent movements recorded by acoustic telemetry, although it was less able to predict the direction of displacement. This first probabilistic assignment to origin for riverine species using a dual‐isotope isoscape technique demonstrated that where the required spatial resolution of animal movements in freshwater is moderately broad (5–10 km), dual‐isotope isoscapes can provide a reliable alternative or complementary method to telemetry.

COMPOSITION AND STATE OF ICHTHYOFAUNA OF SMALL RIVERS OF THE DZHUNGAR ALATAU (ALAKOL BASIN) BY THE EXAMPLE OF SHYNZHYLY RIVER

Until now, the species composition and state of the ichthyofauna of small rivers in the Alakol basin have not been sufficiently studied. Such rivers are characterized by rapid changes in ecosystems, their ichthyofauna is most sensitive to the action of various anthropogenic and natural factors. It was found that in 2015-2017 and 2020 ichthyofauna composition of the Shynzhyly River experienced dramatic changes. Based on the studies carried out in the ichthyofauna of the Shynzhyly River, 9 species of fish were found belonging to 2 families of the order carp: naked osman Gymnodiptychus dybowskii (Kessler, 1874), Balkhash marinka Schizothorax argentatus (Kessler, 1874), Balkhash minnow Rhynchocypris poljakowii  (Kessler, 1879), spotted stone loach Triplophysa strauchii (Kessler, 1874), plain thicklip loach Triplophysa labiata (Kessler, 1874),   Tibetan stone loach Tryplophysa stoliczkai (Steindachner, 1866), Sewertzov’s stone loach Triplophysa sewerzowii (G. Nikolsky, 1938), freshwater bream Abramis brama orientalis (Berg, 1949) and stone moroko Pseudorasbora parva (Temminck et Schlegel, 1846). The fish community mainly consisted of native species. The most numerous were the naked osman, the Balkhash marinka, and the spotted stone loach. Thus, the Shynzhyly River is a reserve of aboriginal ichthyofauna and an important reproduction site for the Balkhash marinka and naked osman. Key words: Shynzhyly River, fish fauna, indigenous, alien, species composition, numbers.

Level of natremia as an index of the condition of the organism of animals under stress

In the diagnosis of stressful conditions in humans and other animals, ionic indicators remain practically unused. In this work, we studied the changes in the concentrations of sodium ions in the blood plasma of freshwater fish under stress caused by stressors of different quality and quantity. Most of the experiments were carried out on adult bream (Abramis brama L) from the Rybinsk Reservoir. Separate experiments were duplicated on adult individuals of roach (Rutilus rutilus L.), pike (Esox lucius L.), and blue bream (Abramis ballerus L.). The concentration of cations in the blood plasma was determined using a Flapho-4 flame photometer. Under the action of mild and short-term stressors of different qualities, the sodium concentration in the internal environment altered toward an increase in concentration gradients on the cell membrane (eustress or physiological stress). Hypernatremia was approximately 10%. Under the action of strong and/or prolonged stressors of different strength, the sodium concentration in the internal environment changed toward a decrease in concentration gradients on the cell membrane (distress or pathological stress). Hyponatremia was 50% in the conditions of acute lethal stress, 20% in subacute lethal stress, 10% or more in chronic lethal stress. During strong acute reversible stress, hyponatremia could reach 30%. Analysis of the material on mammals allowed us to conclude that the adaptation mechanisms in fish and higher vertebrates are similar. In this work, for the first time, the state of the system of electrolyte balance of animals under stress was analyzed from the standpoint of the leading role of ionic concentration gradients on the cell membrane (mainly sodium) in the energetics (level of disequilibrium) of the organism. We propose a concept that in normal and extreme conditions fish use two different defense reactions (or adaptation strategies): active and passive, consisting, respectively, in increasing or decreasing the level of disequilibrium (energy) in the organism. The hyponatremia recorded by numerous authors, which accompanies diseases in humans, is evidently a nonspecific reaction of the organism and serves as an indicator of reduced energy of the organism. It is suggested that the sodium level in the internal environment of the organism be used for diagnosing the stress state of animals.

EDNA metabarcoding survey of fish communities in the Danube and its tributaries

In complement to the JDS4 traditional fish survey (TFS, mainly by electrofishing), a fish eDNA metabarcoding-based survey has been implemented within the framework of the monitoring program organized by DNAqua-Net and in collaboration with the INTERREG "MEASURES" program. Water samples were collected at 29 sites from the source to the mouth of the Danube River, and at 18 tributaries. Two water samples (mean volume 29 L per sample) were collected at each site and the water filtered in situ. Twelve PCR replicates were performed per sample using teleo primers. In total, 80 taxa were detected, of which 19 corresponded mainly to farmed fish or food fish due to eDNA release in waste waters, most often downstream of large cities. Of the remaining 61 taxa, 50 taxa were identified at the species level, six taxa at the genus level, and five taxa at a higher taxonomic level. Concerning the Danube river itself, 69 and 57 species/markers were detected along the Danube River by TFS and eDNA surveys, respectively. 50 of these taxa were detected by both methods. Nine species were captured by TFS alone, mainly due to gaps in reference librairies and too colosely related barcodes. Eight species were only detected by eDNA. Except for the Salvelinus group, these were all benthic species, which are difficult to catch by electrofishing in large rivers (Acipenser ruthenus, Acipenser stellatus, Benthophilus sp., Romanogobio uranoscopus, Sabanejewia balcanica, Umbra krameri). The species richness tended to increase from upstream to downstream and the relative number of DNA sequences per taxa showed a clear succession of species along the river. Barbatula barbatula, Cottus gobio, Hucho hucho, Lampletra planeri, Phoxinus phoxinus and Thymallus thymallus were restricted to the Upper Danube whereas A. ruthenus, Neogobius fluviatilis, S. balcanica and Scardinius erythrophtalmus were detected from Vienna to the Danube river mouth. Abramis brama, Alburnus alburnus, Cyprinus carpio, Silurus glanis, Sander spp, Zingel streber were detected all along the river course; Alosa spp. and Syngnathus abaster downstream from the Iron Gate; A. stellatus and U. krameri only on the most downstream site (Danube delta). The calculation of a fish index, based on the common metrics used to intercalibrate national fish assessment methods on a European scale, classified most of the sites as being in moderate ecological status. Comparison of the indicative ecological status calculated using the same assessment method based on TSF and eDNA data at the common Danube sites showed a similar classification for six of the 13 sites and a difference of one class for the remaining seven sites.

Dynamics of morphobiological parameters of bream Abramis brama (Cyprinidae; Cypriniformes; Actinopterygii) in the Kapshagai reservoir (Balkhash basin)

The morphological and biological characteristics of fish are largely determined by environmental conditions. The study of the variability of fish makes it possible to assess their ecological plasticity and the state of the habitat. A comparative study of morphological variability in the temporal aspect of the bream Abramis brama (Linnaeus, 1758) from the Kapchagai reservoir was carried out. The state of biological indicators, plastic and counting characteristics of samples from 1974, 1992 and 2020 was studied. The method of principal components was used for statistical analysis. The 2020 sample is distinguished by better body condition, but smaller fish sizes. Over the past 28 years, there has been a significant change in the external morphology of bream. The hydrodynamic parameters and the shape of the head have changed. The noted changes may be the result of changes in the ecological niche. At present, the homeostasis of bream development is disturbed in the Kapchagai reservoir, however, high ecological plasticity allows this species to exist in changing environmental conditions

Influence of Amorphous Phenol and Its Fractions on the Activity of Fish Intestinal Peptidases

The in vitro effects of amorphous phenol and its liquid fractions formed 12 months after production were studied in seven freshwater bony fish species: the common carp Cyprinus carpio L., bream Abramis brama (L.), silver bream Blicca bjoerkna (L.), roach Rutilus rutilus (L.), perch Perca fluviatilis L., and sander Zander lucioperca (L.). The study revealed that the effects of amorphous phenol and its liquid fractions are species-specific and depend on the concentration of phenol and localization of peptidases (intestine mucosa or intestinal cavity in case of chyme). The specific features of the effect of amorphous phenol differ considerably from the effect of crystalline phenol.

Determination of Pharmaceuticals, Heavy Metals, and Oxysterols in Fish Muscle.

The present study aimed to assess the levels of 98 multi-class pharmaceuticals including cardiovascular drugs, antidepressants, hypnotics, antibiotics, and sulfonamides occurring in the muscle tissue of fish caught in the Baltic Sea. The following fish species were collected: perch (Perca fluviatilis); flounder (Platichthys flesus); turbot (Scophthalmus maximus); plaice (Pleuronectes platessa); cod (Gadus morhua callarias); bream (Abramis brama); crucian (Carassius carassius). Additionally, in the examined fish muscle the levels of heavy metals and trace elements were determined (As; Ag; Au; Ba; Cd; Co; Cr; Cu; Hg; Li; Mo; Ni; Pb; Sb; Se; Sn; Tl; V) as well as the levels of cholesterol and its 5 derivatives (7-ketocholesterol; 7α-hydroxycholesterol; 7β-hydroxycholesterol; 5β,6β-epoxy-cholesterol; 5α,6α-epoxycholesterol). In the performed studies 11 out of 98 examined pharmaceuticals were detected in fish muscle. The levels of pharmaceuticals in fish muscle varied depending on the species. In the tissues of bream and crucian, no pharmaceuticals were found. Mercury, lead and arsenic were detected in the muscles of all examined fish. Based on the hazard factor for Hg, Pb, Cd, Ni (target hazard quotient, THQ < 1), it was found that the consumption of the studied fish does not constitute a health risk. However, the THQ for As remained >1 indicated possible risk from those metals. In the examined fish muscle the total cholesterol oxidation products (COPs) level of oxysterols were, respectively: 6.90 (cod) μg/g–4.18 μg/g (perch), which corresponded to 0.7–1.5% of cholesterol. The main COPs evaluated were 7-ketocholesterol (0.78 ± 0.14–1.79 ± 0.06 μg/g), 7β-hydroxycholesterol (0.50 ± 0.04–3.20 ± 2.95 μg/g) and 5β,6β-epoxycholesterol (0.66 ± 0.03–1.53 ± 0.66 μg/g). The assessment of health hazards due to contaminations is necessary, which may help to introduce national legislation and global standards aimed at reducing or even eliminating the exposure to contaminants.