Abramis Research Articles

On the problem of annual overfishing of the silver bream Blicca bjoerkna (Cyprinidae) in industrial fishing in the Astrakhan region

The silver bream Blicca bjoerkna and the small-sized common bream Abramis brama are characterized by external similarity, which contributes to manipulations with the substitution of one species (common bream) by another (silver bream) when taking into account the volume of industrial fishing in the Astrakhan region. This is due to the fact that in the period of spring fishing season during common bream spawning migration, the share of non-commercial common bream in commercial catches increases (to 20–30 %), the catch of which is limited in accordance with the Fishing Rules. In order not to exceed the allowable volume of by-catch of non-large common bream, fish producers register en masse catches of small-sized bream as a catch of silver bream, which causes significant damage to common bream fish stocks through oversampling of first-time maturing individuals of the population. In recent years, the share of non-commercial common bream recorded as a silver bream in May alone is 13–28% of its official catch during this period. In order to reduce the catch of first spawning common bream producers of non-commercial length on the water bodies of the Astrakhan region in the period from April 21 to May 20, it is recommended to introduce a ban on industrial fishing of silver bream.

Comparative analysis of fisheries and biological characteristics of bream (Abramis brama) in Saratov and Volgograd reservoirs

Based on the results of ichthyological surveys and industrial catch data, a comparative analysis of the commercial biological characteristics of bream in the Saratov and Volgograd reservoirs was carried out. The material was the results of expeditionary research by employees of the Saratov branch of the VNIRO. With the existing fishery, bream stocks are in a stable condition. The volumes of commercial stocks and catches of the species in question in the Volgograd Reservoir are higher than in the Saratov Reservoir. Despite differences in fishing intensity and characteristics of reservoirs, the size and weight indicators of the species are similar.

Individual variability in the movement ecology of Northern pike Esox lucius in a highly connected wetland system

Maintaining hydrological connectivity is important for sustaining freshwater fish populations as the high habitat connectivity supports large-scale fish movements, enabling individuals to express their natural behaviours and spatial ecology. Northern pike Esox lucius is a freshwater apex predator that requires access to a wide range of functional habitats across its lifecycle, including spatially discrete foraging and spawning areas. Here, pike movement ecology was assessed using acoustic telemetry and stable isotope analysis in the River Bure wetland system, eastern England, comprising of the Bure mainstem, the River Ant and Thurne tributaries, plus laterally connected lentic habitats, and a system of dykes and ditches. Of 44 tagged pike, 30 were tracked for over 100 days, with the majority of detections being in the laterally connected lentic habitats and dykes and ditches, but with similar numbers of pike detected across all macrohabitats. The movement metrics of these pike indicated high individual variability, with total ranges to over 26 km, total movements to over 1182 km and mean daily movements to over 2.9 km. Pike in the Thurne tributary were more vagile than those in the Ant and Bure, and with larger Thurne pike also having relatively high proportions of large-bodied and highly vagile common bream Abramis brama in their diet, suggesting the pike movements were potentially related to bream movements. These results indicate the high individual variability in pike movements, which was facilitated here by their access to a wide range of connected macrohabitats due to high hydrological connectivity.

Complete mitochondrial genomes of Dactylogyrus crucifer and Dactylogyrus zandti reveal distinct patterns of codon usage within Dactylogyrus

Monogeneans of the genus Dactylogyrus Diesing, 1850, the largest genus in the family Dactylogyridae, mostly parasitize the gills of cyprinoid hosts; however, only 3 Dactylogyrus’ mitochondrial genomes (mitogenomes) are studied so far. The aim of this research is to extend our understanding of the mitogenomes of Dactylogyrus. We sequenced the mitogenomes of D. crucifer and D. zandti isolated from Rutilus rutilus and Abramis brama orientalis in northwest China, and then we compared these mitogenomes with other monogeneans. We used Illumina NovaSeq to sequence the entire mitochondrial genomes of D. crucifer and D. zandti and characterized the mitogenomes to understand the gene structure, gene identity, the secondary structures of the 22 tRNA genes, and relative synonymous codon usage. We used the analytic Bayesian Information and Maximum Likelihood methods to determine their associated phylogenetic trees. The mitogenomes of D. crucifer and D. zandti were 14,403 and 18,584 bp, respectively. Organization and positioning of these genes were in accordance with Dactylogyrus lamellatus and Dactylogyrus tuba. The nucleotide composition of Dactylogyridae was different from other families of Monogenea, and the A+T count of genus Dactylogyrus (54 – 58.4 %) was lower than other genus species of the family Dactylogyridea (63.9 – 78.4 %) in protein-coding genes. Dactylogyrus members displayed a codon usage bias. The relative synonymous codon used by Dactylogyrus was not conserved and was lower than other monogeneans. The codon use patterns of closely-related species isolated from closely-related hosts were identical. Phylogenetic analyses using mitogenomic dataset produced Dactylogyrus isolated from host subfamily Leuciscinae formed a sister-group. Our results contributed significantly to an increased database of mitogenomes, more than 50 %, for Dactylogyrus that may help future studies of mitochondrial genes and codon uses for the analysis of monogenean phylogenetics.

Relationship between mean monthly February temperature and the level of oxidative processes in immunocompetent organs of bream of Rybinsk reservoir in different years

The intensity of oxidative processes in immunocompetent organs of immature bream Abramis brama L. with an average weight of 375±30 g and length of 290±20 cm was studied. The fish were caught with shuttle nets in the Volga Plec of the Rybinsk reservoir in different years in terms of average daily temperature conditions. After autopsy, samples of immunocompetent organs (kidney, spleen and liver) were taken from captured fish into sterile tubes. Samples were then frozen and stored in a freezer at minus 18–20 °C until processing time. In laboratory conditions, samples were thawed at room temperature immediately before analysis. For further studies, homogenate was prepared from kidney, spleen and liver tissues using a homogenizer with physiological solution in the ratio of 1:1. In the homogenates the content of lipid peroxidation products was studied by the content of malonic dialdehyde and the level of antioxidant defense by the index of inhibition of substrate oxidation. The interannual variability of the studied parameters was noted, associated with ecological and climatic conditions, in particular, with temperature. The most significant differences of the studied biochemical parameters were revealed in the year with the highest temperature conditions compared to the year with the lowest temperature. The lowest values of malonic dialdehyde and substrate oxidation constant were observed in fish in the year with the lowest average daily temperature. In warmer year intensification of lipid peroxidation processes and decrease of antioxidant defense level in the studied organs were observed. The results obtained can be used in monitoring the impact of climatic factors on the physiological and biochemical status of fish.

Genetic Features of the Bream Abramis brama Population from the Lake System of Sebezhsky National Park

The genetic variability of microsatellite DNA has been studied for the first time for five loci in the common bream Abramis brama (L.) from lakes Sebezhskoye and Necheritsa of the Sebezhsky National Park lake system (Pskov oblast). The results demonstrate the uniformity of estimates of the genetic variability of the bream in the lake system. Estimates of the allelic diversity of microsatellite loci and the expected heterozygosity of local bream groups do not differ significantly. The total genetic differentiation of bream is θ = 0.004, 95% CI (–0.01; 0.01), and is statistically insignificant. The Bayesian analysis of the studied multilocus genotypes has not revealed any population–genetic structure. The results indicate a high level of gene flow between local bream groupings and make it possible to assume the presence of a genetically unified panmixed population in the Sebezhsky National Park lake system.

Характеристики эласмоидной чешуи рыб и ее фракций, по данным ИК-Фурье-спектроскопии

Elasmoid scales of pike-perch (Sander lucioperca), white amur (Ctenopharyngodon idella), carp (Cyprinus carpio), freshwater bream (Abramis brama) and crucian carp (Carassius carassius) were processed without hydrolysis by “dry” method in order to study the characteristics of the obtained finished product, which determine its further use as additives for food and other purposes. The essence of the method consisted in washing the scales, its subsequent drying, grinding and separation, with obtaining two fractions enriched with both organic (cotton-like product) and inorganic (powder) components. FT-IR spectroscopy was used to characterize the scale samples and their enriched fractions. Characteristic bands known for collagen, in particular for Amide I, Amide II, Amide III, Amide A, were observed in the IR spectra of all the samples studied. The bands (inorganic part) at ~1022 cm–1 and at ~599 cm–1 indicate valence asymmetric vibrations of PO43– groups. Numerous bands for all experimental samples in the wavelength region 3900-3500 cm–1 can be caused by vibrations of OH groups, which is associated with the presence of water in the tested samples. Comparison of the absorption intensity in the region of characteristic frequencies of collagen and hydroxyapatite calculated by the IR method can be one of the approaches for the development of a rapid method for the determination of their quantitative content in fractions obtained from fish scales. Organic and mineral additives from fish scales can be recommended as components of formulations of various food products, as well as raw materials in tissue engineering, orthopedics and dentistry.

Fish of Low Commercial Value in Lakes of Different Trophic Status (Poland)

In a commercial fishery, some fish are classified as low-value, but their classification varies in different countries. The aim of this study was to determine the abundance, contribution, and dominance of low-value fish species, such as Abramis brama < 1000 g, Alburnus alburnus, Blicca bjoerkna, Gymnocephalus cernua, Perca fluviatilis < 100 g, Rutilus rutilus < 200 g, and Scardinius erythrophthalmus < 200 g, in 145 Polish lakes of different areas, depths, and trophic statuses situated in the northern and central parts of Poland in 2021. Perca fluviatilis and R. rutilus were the most frequent low-value species (100% and 99%, respectively). The contribution of all low-value fish to the total biomass of caught fish was relatively high, ranging from 37% in the mesotrophic lake to 100% in the eutrophic lake (mean of 77 ± 14%). Lakes in which the contribution of low-value species exceeded 90% were relatively numerous (24 lakes, 17% of the studied lakes). Among a total of about 437.5 thousand low-value fish, 261 thousand specimens (60%) had a body weight of below 10 g. All low-value fish species, except for P. fluviatilis and S. erythrophthalmus, were related to the studied environmental variables. The relative biomass of these species increased with increasing lake productivity, while it decreased with the increasing maximum and mean depth of the studied lakes. The high contribution of low-value fish to the total biomass in many lakes indicates the need for the constant monitoring of the abundance and structure of fish communities and the use of appropriate actions (biomanipulation and stocking with piscivorous fish species) to improve the ecological condition of lakes.

Variability in the summer movements, habitat use and thermal biology of two fish species in a temperate river

The ability of fish to cope with warm water temperatures in summer depends on factors including their thermal traits and the ability of individuals to access cool-water refugia. Knowledge is highly limited on the in situ responses of many fishes to elevated summer temperatures, including whether they express behavioural thermoregulation. The responses of two riverine species to summer water temperatures were tested here using the movement metrics, spatial habitat use and body temperatures of individual European barbel Barbus barbus (‘barbel’) and common bream Abramis brama (‘bream’) versus river temperatures. Acoustic biotelemetry was applied in the lower River Severn basin, western Britain, in summer 2021 (barbel) and 2022 (bream), where individuals could move across > 150 km of river, including a tributary of cooler water. Across all individuals, bream occupied 37 km of river length (mainstem only), with low inter-individual variability in their spatial habitat use, movements and body temperatures. In contrast, barbel occupied 62 km of river (main river/tributary), with relatively high inter-individual variability in spatial habitat use, movements and body temperatures, with higher variation in body temperatures as river temperatures increased (maximum mean daily temperature difference between individuals on the same day: 4.2 °C). Although warmer individuals generally moved more, their activity was greatest at relatively low temperatures and higher flows, and neither species revealed any evidence of behavioural thermoregulation during elevated temperatures. Enabling phenotypically diverse fish populations to express their natural behaviours and thermal preferences in summer water temperatures thus requires maintaining their free-ranging in thermally heterogenous habitats.

Temperature-related increase in growth rate in four freshwater lake fish species.

Growth is one of the most direct and common ways fish respond to climate change, as fish growth is intimately linked to the temperature of the environment. Observational studies on the effect of shifts in temperature on fish growth are scarce for freshwater fish, and particularly lacking for lake populations. Here, changes in growth rate of bream (Abramis brama), perch (Perca fluviatilis), pikeperch (Sander lucioperca), and roach (Rutilus rutilus) over three decades were studied and compared with changes in temperature in the two largest lakes of western Europe: Lake IJsselmeer and Lake Markermeer in the Netherlands. In the autumnal survey catches of bream, perch, and roach, the mean length of YOY increased significantly between 1992 and 2021 in both lakes, but for YOY pikeperch, no temporal changes were found. In a length-stratified dataset of age groups of bream, roach, and perch, the relationship between length and age differed significantly between time periods. In the more recent time periods, indications for higher growth rates across multiple ages were found. Temperature during the growth season increased in the same decades and showed significant correlations with the YOY mean length, for bream, perch, and roach in both lakes, and for pikeperch in Lake Markermeer. These results point toward consistent temperature-induced increases in growth over the age groups for bream, roach, and perch. These increases were found despite the simultaneous process of de-eutrophication in this water system and its potential negative effect on food production. For pikeperch, it is hypothesized that the absence of temporal increase in YOY growth rate is related to its necessary switch to piscivory and subsequent food limitation; the lower thermal range of its main prey smelt, Osmerus eperlanus, is hypothesized to have inhibited food availability for YOY pikeperch and its opportunity to achieve higher growth rates.

Replicated whole‐lake experiment reveals the ineffectiveness of stocking five example fish species in small lakes

AbstractFish stocking is common practice in fisheries management, but its effectiveness to support or increase stock size or catches is debated. In Lower Saxony, Germany, a controlled, replicated stocking experiment of five native fish species in eight gravel pit lakes <20 ha was conducted to examine the potential additive effects of fish releases on abundance, indexed by catch per unit effort (CPUE) in electrofishing and gillnet samples. Fish were stocked twice in four study lakes, while the remaining four control lakes were not subjected to any stocking over a 6‐year study period. Recapture rates of individually marked fishes were extremely low in all five species. Consequently, stocking did not increase species‐specific and total fish community abundance. In additional control experiments in separate ponds all stocked fish species, except bream (Abramis brama), showed high survival in at least one study year, indicating general survival of the stocking material. Fish marking with passive integrated transponders did not affect fish survival, except for roach (Rutilus rutilus), and can thus be ruled out as an explanation for the high post‐stocking mortality. We conclude that stocking failed to enhance stocks of five native fish species in small gravel pit lakes.

Percentage of Leukocytes in Peripheral Blood, Head Kidney, and Spleen of the Abramis brama (Cyprinidae) Bream of the Upper Volga Reservoirs

Percentage of Leukocytes in Peripheral Blood, Head Kidney, and Spleen of the Abramis brama (Cyprinidae) Bream of the Upper Volga Reservoirs

Water quality in a shallow eutrophic lake is unaffected by extensive thinning of planktivorous and benthivorous fish species

Ambitious to fulfill the European Water Framework Directive obligations, the European governments support projects to rehabilitate lakes with poor water quality. However, most lake restorations having relied on biomanipulation by fish thinning have failed to improve or even maintain water quality. Previous attempts removed all target fish species simultaneously, thus making it impossible to assess the specific impact of each feeding group on water chemistry. Lake Bromme was selected for extensive, time-selective fish biomanipulation to improve water clarity and promote submerged macrophytes and piscivorous fish stocks over a three-year monitoring period. Thinning of adult benthivorous bream (Abramis brama) and tench (Tinca tinca) was conducted throughout year one while thinning in years two and three targeted planktivorous roach (Rutilus rutilus), juvenile bream, and small perch (Perca fluviatilis). Yearly fish surveys assessed changes in fish population structure and biomass. Water quality parameters were monitored continually, and the cover of submerged macrophytes was surveyed annually via sonar. We found no improvement in water clarity or reductions of nutrients, organic particles, chlorophyll concentrations, or watercolor, despite a 6-fold thinning of total estimated fish biomass, from 112 to 19 kg ha−1. Over the period, the macrophyte cover increased from 0.8 to 13.5 %, but no recruitment of large piscivorous fish (perch and pike (Esox lucius) > 10 cm) was detected. We found higher correlations of particle concentration and water clarity to water temperature than to wind speed, which indicates sediment particle resuspension by the remaining fish community (mostly carp Cyprinus carpio) that forage on benthos in shallow lakes. Further system-ecological research in Lake Bromme should evaluate whether thinning the stock of carp and increasing plant cover may improve water quality and test which optical properties sustain high water turbidity and prevent shallow, eutrophic lakes like Lake Bromme from responding to intense fish thinning.

МИКРОБИОЛОГИЧЕСКАЯ БЕЗОПАСНОСТЬ СВЕЖЕЙ РЫБЫ, ЗАРАЖЕННОЙ ТРЕМАТОДАМИ, С УЧЕТОМ САНИТАРНОГО СОСТОЯНИЯ ВОДОЕМОВ

The purpose of research is to study the relationship between the microbiological indicators of fish infected with diplostomosis and post-diplostomosis, and the indicators of veterinary and sanitary safety of water bodies involved in its cultivation. Objectives: determination of the main parasitological indicators of infected fish (intensity of invasion (II), extensiveness of invasion (EI), species predisposition of fish to pathogens of trematodes); conducting a microbiological analysis of the obtained fresh fish and the place of its cultivation, taking into account the degree of infestation of the fish by pathogens of diplostomosis and post-diplostomosis. The study was conducted in the conditions of the North Caucasus Zonal Research Veterinary Institute in the summer and autumn seasons of the year. The study material included fish of different species: Hypophthalmichthys molitrix (silver carp), Cyprinus carpio (carp), Ctenopharyngodon idella (grass carp), Abramis brama (Bream), both infected with trematodes and clinically healthy. The water of the fish catchment site, taken from the Nizhnedonsky canal, Veselovsky, Proletarsky and Tsimlyansky re¬servoirs, was studied. The lowest AI and EI were found in fish of the species Ctenopharyngodon idella (grass carp). AI in silver carp compared to grass carp was 11.3 times higher, in carp – 9.3 times, in bream – 6.6 times; EI was 11.3 times higher in silver carp and 11.0 times higher in carp; for bream – 3.3 times. In highly invasive fish of the species Hypophthalmichthys molitrix (silver carp), Cyprinus carpio (carp), mesophilic aerobes and facultative anaerobic microorganisms were found to be 14.7 and 4.24 times more, respectively, compared to healthy fish; according to the average value of detected coliform bacteria – 2.54 and 1.86; by the number of detected Staphylococcus sp. – at 24.3 and 33.15; Escherichia sp. – at 1.5 and 0.6; Klebsiella sp. – at 110 and 85; Salmonella sp. – 45 and 0.8 times more. A correlation was established between the total microbial number of water bodies and the number of mesophilic aerobes and facultative anaerobes in caught live fish (correlation coefficient 0.99).

Decline of Artisanal Fish Catch by Species in the Croatian Section of the Sava River

Abstract The aim of this study is to analyse the development of artisanal fish catch by species in the Croatian section of the Sava River. For Abramis brama and Silurus glanis, a significant decline in catches (in kg) was observed throughout the study period (2004-2021). Since 2013, this has also been the case for Cyprinus carpio, Esox lucius, Sander lucioperca, other autochthonous species and alochthonous species, while catches of Leuciscus idus have declined significantly since 2014. The catches of three species (Acipenser ruthenus, Leuciscus aspius and Tinca tinca) fluctuated without a trend, which can be attributed to the low quantities. This decline in catches of the most sought-after species in the Sava was greater than that of the other less sought-after autochthonous species (mainly other cyprinids), whose share of the total catch increased significantly.

Assessment of the bream <I>Abramis brama</I> (cyprinidae) stock of the Nizhnekamsk reservoir with limited data available

An analytical assessment of the state of the bream stock in the Nizhnekamsk reservoir was carried out using the method for stocks with limited data – CMSY (Catch-based method). The results obtained indicate sufficient reliability of the use of this model for the bream stock, based on data from official catch statistics of this species. The calculations showed that during the history of exploitation of this population, fishing was carried out mainly in a zone biologically safe for the stock. Since 2017, the catch of bream has increased sharply and currently the fishing volumes are at their maximum values for all the years of the reservoir’s existence. The indicators of current estimates of the stock biomass and fishing mortality exceed their target guidelines and indicate that at the moment the biomass of the bream stock of the Nizhnekamsk reservoir is already in a biologically unsafe zone, and fishing mortality is twice the level of target exploitation.

МОНИТОРИНГ ВОЗБУДИТЕЛЕЙ ОСНОВНЫХ ПАРАЗИТОЗОВ ВОДНЫХ ПТИЦ НА ИЗОЛИРОВАННОЙ ПРИРОДНОЙ ТЕРРИТОРИИ НАЦИОНАЛЬНОГО ПАРКА «ЛОСИНЫЙ ОСТРОВ»

An important point in the conservation of biological diversity and avifauna resources on the territory of national and zoological parks, reserves, as well as commercial breeding poultry enterprises is the study of the bioecology of parasitosis pathogens. In this study, for the first time in a long time, the results of bioecological monitoring of the main parasitoses of aquatic birds living in the isolated natural territory of NP "Losiny оstrov" are presented. The main focus of the work was the study of the spread of the invasive origin in intermediate, additional and final hosts, as well as the conservation potential of aquatic bird species and other components of the biogeocenosis. The article presents the results of helminthological studies of feces of birds of the gull families (lake gull Larus Ridibundus) and duck (mallard Anas Platyrhynchos); helminthological studies of the gastrointestinal tract of fish of the cyprinid family (bream Abramis Brama) and firebrand (perch Perca Fluviatilis); mollusks of the family Lymnaeidae and the family Planorbidae. 85 and 86 individuals of fish and shellfish, respectively, and 116 samples of bird droppings were studied. The number of identified samples from seagulls was 23, from ducks – 47, the remaining 46 samples were defined as «blind samples». The main composition of intestinal parasites of aquatic birds and aquatic organisms has been revealed. Data were obtained on the infection of aquatic birds with associative helminth-protozoal mixinvasion: genera – Eimeria and Trichomonas and helminths of genera: Capillaria, Amidostomum, Heterakis. At the same time, the presence of mixed invasion was noted in 64.28% of the total number of samples. Data were obtained on the infection of fish and shellfish, the helminth fauna of which is represented by the families Echinoctomatidae and Diplostomum sp. The extent of monoinvasion of mollusks of the species Lymnaea stagnalis by cercariae and metacercariae of trematodes of the family Echinoctomatidae was 62.16%.

Структурні показники та динаміка промислових уловів риб дніпровських водосховищ

Purpose: to establish and analyze the dynamics of the species composition and amounts of commercial fish catches over the past 10 years in the context of assessing the overall efficiency of the fishery exploitation of Dnieper reservoirs. Methodology. As primary materials, data from official commercial fishery statistics and the results of field monitoring studies carried out by the Institute of Fisheries of the National Academy of Sciences on Dnieper reservoirs in the period of 2012‒2022 were used. The intensity of commercial fish harvest was assessed by the annual fishing mortality rate, which was defined as the difference between the total and natural mortality. The total mortality rate was determined graphically by the natural logarithms of the number of age groups in catches; natural mortality — based on the parameters of the von Bertalanffy equation. Statistical data processing was carried out in MS Excel. Findings. The dynamics of commercial catches in the cascade of Dnieper reservoirs in the last 10 years has been characterized by instability with a minimum of 8.9 thousand tons in 2013 and a maximum of 14.0 thousand tons in 2019. The majority of commercial catches was Prussian carp (28.2% of the total catch), common bream (21.1%), roach (20.5%) and silver bream (8.3%). The catch dynamics of all limited species had the same features — a growth in the period 2014‒2016, stabilization until 2019 and a further decrease, which was due to the determining influence of organizational factors. The distribution of fishing pressure by the objects of fishing does not fully correspond to the quantitative parameters of their ichthyomass; the average (2019‒2021) coefficients of annual fishing mortality were: pikeperch — 32.0%, common bream — 22.8%, roach — 24.2%, silver bream — 22.7%, Prussian carp — 19.0%. The maximum catches per unit effort of the gill net in the studied period were recorded for the Kamianske reservoir (348.9±73.4 kg), the lowest (152.0±44.5 kg) — for the Kaniv reservoir. The average fish catch per one gill net per cascade was 245.1±36.3 kg; a trend towards its growth during 2012‒2021 was observed. Originality. Original data on the modern dynamics of the amount and structure of commercial fish catches as a component of scientific support for fisheries exploitation of the Dnieper reservoirs were obtained. Practical value. It has been found that the fluctuations of fish catches in Dnieper reservoirs are largely determined by the influence of external (organizational) factors, which makes it possible to effectively manage the use of fish stocks. It is shown that for some species (in particular, pikeperch), the intensity of fishery exploitation exceeds the optimum, for others (Prussian carp, Black Sea sprat), on the contrary, an increase in the fishing pressure is possible.

TREMATODA AND CESTODA SPECIES IN CYPRINID FISH FROM SMALL LAKES OF THE KOSTANAY REGION

This study presents data on the epizootiological monitoring of parasitic diseases in fish from Kostanay region. It confirms the presence of previously identified permanent natural foci of opisthorchiasis in the southern districts, specifically in the Uly-Zhilanchik and Torgay rivers. Additionally, the research conducted in Zhangeldy and Amangeldy districts revealed the existence of biohelminths with both epizootiological and epidemiological significance. This study aimed to investigate the presence of parasites dangerous to humans and carnivores in cyprinid fish species. Specifically, it focused on identifying the second intermediate hosts for opisthorchiasis, metorchiasis, and ligulosis: ide (Leuciscus idus) and bream (Abramis brama). From 2021 to 2023 seven reservoirs of the Kostanay region were the monitoring objects of the parasitological situation: Verkhnetobolskoe reservoir, rivers: Torgay, Uly-Zhilanchik, Zhaldama, Tobol, Zhelkuar, Akkol Lake, where shellfish bitiniids, waterfowl and crustaceans live in large numbers, as the first intermediate host of pathogens Opisthorchis felineus (Metorchis bilis), Ligula imestinalis. Examination of eight ide (Leuciscus idus) specimens caught in the Uly Zhilanchik River revealed the presence of metacercariae of two parasitic trematodes: O.felineus and M.bilis, while the prevalence was 18.5% and 8.3%, and the infestation intensity was 1-3 and 2, respectively. In the Amangeldy region, metacercariae O. Felineus and plerocercoids Ligula imestinalis were found in two fish species: one individual of the ide species and two individuals of the bream species caught from the Torgai River. At the same time, the prevalence was 6.6% and 16.6%, and the infestation intensity was 2 and 1, respectively. Parasitic diseases of fish were not detected in the waters of Denisovsky and Zhitikarinsky districts. Based on Polymerase Chain Reaction (PCR) analyses conducted using specific primers at the National Center of Biotechnology LLP laboratory in Astana, Kazakhstan, two distinct types of opisthorchid parasites were identified in two ide (Leuciscus idus) specimens collected from Kostanay region. The species were confirmed to be Opisthorchis felineus and Methorchis bilis (PCR protocol dated April 24, 2023).

Biological features of the white bream Blicca bjoerkna (Linnaeus, 1758) from Cuciurgan

The ichthyocenosis of the Cuciurgan reservoir of the Moldovan Thermal Power Plant is home to the common bream, an eudominant species with a dominance index value (D5) of 53.07 % in catches taken with 25 x 25 mm – 40 x 40 mm mesh gillnets. Currently, the number of white bream is at a stable level with a tendency to remain approximately constant over the next few years. The absolute linear dimensions (L) of the common bream in the Cuciurgan reservoir range from 4.8-31 cm, standard length (l) – from 3.8 to 24.5 cm. Body weight reaches 334 g. The gender structure of the common white bream population in this ecosystem demonstrates the dominance of females in the ratio of 2:1. The reservoir’s white bream is characterized by a high fattening ratio, which according to Clark is 1.96 ± 0.013. A small part of the white bream (1.5 %) in the Cuciurgan reservoir uses fish species as trophic resources.