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This study investigates phylogenetic and phylogeographic relationships of Vimba species using mitochondrial cytochrome b (cyt b) (1023 bp) and cytochrome c oxidase subunit I (COI) barcoding region (652 bp) genes. Ninety-one samples from 36 populations for the cyt b gene and 67 samples from 20 populations for the COI were analyzed. We identified 29 haplotypes and calculated overall haplotype diversity as Hd: 0.907 ± 0.015 for cyt b. We also identified 13 COI haplotypes and calculated overall haplotype diversity as 0.826 ± 0.026 for this marker. The phylogenetic analysis of Vimba species reveals the presence of four clades, based on concatenated cyt b and COI sequences. The first and second clade consist of Vimba vimba Western lineage, and Vimba vimba Caspian lineage, while the third and fourth clade consist of Vimba mirabilis and Vimba melanops. Based on haplotype network analyses and phylogeographic inferences, the Vimba genus is monophyletic, and its species dispersed in the Pleistocene era.

Vimba bream (Vimba vimba) individuals were collected from the Danube River near Belgrade, from May 2016 to May 2017. Samples of muscle and liver tissue were analyzed for concentrations of 25 elements (macro-, micro-, and toxic elements) using inductively coupled plasma optical emission spectrometry (ICP-OES). For both tissues, the highest concentrations of most elements were observed in late spring/early summer (months of May and June). Majority of statistically significant correlations between elements were positive in both tissues. Contributions of Ca, K, and Mg to human diet were in a similar range. The lowest contribution of all macroelements was observed for Na, while the contribution of Se was well above the recommended dietary allowance for this element. Levels of detected elements were well below MAC values prescribed by national and international regulations. The highest value of Hg liver/muscle index (>1) was observed in August, which could indicate a higher contamination of the sampling location in that month. Se:Hg molar ratio never drops below 1, which could indicate that Hg toxicity is prevented. THQ values showed little variation thought the year and were well below the threshold of 1, with the exception of THQ for Al in May (0.92). This element also strongly affects the hazard index.

Stock assessment of vimba population Vimba vimba (Linnaeus, 1758) in period 2015–2020 was performed by qualitative indicator method LBI (Length-Based Indicators) that allows to assess qualitative characteristics of the population and fisheries and MSY biological reference points. The indicator, qualitative approach to stock assessment was applied due to absence vimba population of stable stock-recruitment relationship (due to artificial reproduction exist), which makes impossible to apply surplus production approach to solve production equation dB/dt. LBI model was performed based on available length-weight vimba frequencies dynamics information, which allows to evaluate qualitative population characteristics and fisheries impact. Model results shows no overexploitation signals: in period 2015–2020 fisheries are carried out in maximum sustainable yield level. Indicator results according to reference points indicate no significant signals of reduction optimal length class (Lopt), small-size or large-size class. In 2016 and 2018 uncertain overexploitation of small-scale classes leads to no significant changes was underlined. In terms of biological and fisheries data lacking, LBI methods allow to perform stock assessment procedure more stable and robust then surplus or cohort approach, and output scientific advice to fisheries management.

The trace elements (TEs) in aquatic environments due to anthropogenic activities are readily available to aquatic organisms. There are 153 fish species inhabiting the Caspian Sea. However, little is known about TE (TE) concentrations in these species. In this study, we investigated the effects of TEs levels in the brain of some bony fish species inhabiting the Caspian basin. Totally, 405 fish from nine species with different feeding behaviors including Leuciscus aspius (n = 20) and Perca fluviatilis (n = 37) as piscivores, Rutilus kutum (n = 27) and Rutilus caspius (n = 71) as carnivores, Vimba persa (n = 56), Ponticola caspia (n = 25) and Tinca tinca (n = 31) as mollusivores, and Alburnus chalcoides (n = 77) and Alosa braschnikowi (n = 61) as zooplanktivores were collected from the southwest of the Caspian Sea basin from September 2017 to June 2018. The ICP-OES was used to measure TEs in the brain tissue of fish. The variability of TEs concentrations in the brain tissues of these fishes by principal component analysis (PCA) was decreased to 63.59% and 17.68% for PC1 and PC2, respectively, exhibiting that 81.27% of the total variability is associated with K, Mg, P, S, Zn, and Al. The two-dimensional diagrams showed the weight of each component in PCA. The PC1 was mostly influenced by P, Mg, K, and Zn, while the greatest value in PC2 belonged to Al. Furthermore, the entire number of elements determined in this study was found to be a suitable indicator for the distinction between fish species based on their feeding items.

This paper presents recent data on the population of the anadromous vimba bream (Vimba vimba vimba), introduced in the Volga basin. After penetration to the downstream section of the Volga River from the Volgograd Reservoir, vimba bream can be found throughout the entire unregulated stretch downstream of the Volga Hydroelectric Station. Observations show that the population size changes naturally during the year owing to its spawning migration. At the same time, a gradual transformation of the seasonal dynamics of the species is observed. As populations spread further downstream, the migrations of spawners downstream of the dam become longer, and the population density decreases. Also a seasonal redistribution takes place, with reduced migration observed in autumn and increased migration during spring. Meanwhile, the growth rate in the downstream section of the Volga River is comparable to the growth rate of populations in the Volgograd and Tsimlyansk reservoirs. Spawning occurs on in-channel spawning grounds. Yearlings are observed over a distance of 100 km downstream of the dam. In addition to Vimba bream, single specimens of Caspian bream (V. v. persa) are also recorded.

The feeding habits of two omnivorous fish species, Vimba vimba (L., 1758) and Scardinius erythrophthalmus (L., 1758) from the Buyukcekmece Reservoir (Turkey) were investigated through stomach content analyses. Samplings were carried out monthly to describe the dietary composition of two species and to assess whether it overlapped. The diet spectrum of V. vimba consisted of eight prey categories: Diptera, Insecta extremities, plants, Cladocera, Bivalvia, Ostracoda, Pisces and detritus. Detritus has the highest value in terms of modified index of relative importance and it was followed by Insecta. The diet composition of S. erythrophthalmus consisted of four prey categories: Insecta extremities, plants, Bivalvia and detritus. Plant has the highest value in terms of modified index of relative importance and it was followed by detritus. No dietary overlap was detected, except for the fish collected in spring. Fractional trophic level (TROPH) and its standard error (SE) were estimated as 2.62±0.25 for V. vimba and 2.45±0.19 for S. erythrophthalmus.

Simple Summary It is important to consider the nutritional requirements and optimum feeding of hatchery-raised, conservation-priority rheophilic fishes meant for river stock enhancement. Properly selected diets for these nutritionally data-poor fish species are crucial to achieve optimum growth potential and physiology. It greatly reduces the time spent in captivity, and if properly trained, may produce fish that are better insured for facing hardships in the wild. Abstract Large-bodied, river-migrating, rheophilic fishes (cyprinids) such as barbel Barbus barbus, nase Chondrostoma nasus, asp Leuciscus aspius, and vimba bream Vimba vimba are threatened in major European drainages. This represents the subject of our present study. Their hatchery nutrition prior to river-release is mostly on a hit-and-trial or carp-based diet basis. The study demonstrates an alternative approach to decide optimum nutrition for these conservation-priority and nutritionally data-poor fishes. The study revealed barbel as a central representative species in terms of wild body composition among other native rheophilic cyprinids considered (asp, nase, vimba bream). Taking barbel as a model, the study shows that barbel or rheophilic cyprinids may have carnivorous-like metabolism and higher requirements of S-containing, aromatic, branched-chain amino acids (AAs) than carps. Besides, there are important interactions of AAs and fatty acids (FAs) biosynthesis to consider. Only proper feeding of nutritionally well-selected diets may contribute to river stocking mandates such as steepest growth trajectory (≈less time in captivity), ideal size-at-release, body fitness (≈blend-in with wild conspecifics, predator refuge), better gastrointestinal condition, maximized body reserves of functional nutrients, and retention efficiencies (≈uncompromised physiology). Considering important physiological functions and how AA–FA interactions shape them, hatchery-raised fishes on casually chosen diets may have high chances of physiological, morphological, and behavioral deficits (≈low post-stocking survivability). Based on the observations, optimum nutrient requirements of juvenile (0+ to 1+ age) barbels are suggested. Future efforts may consider barbels as a nutrition model for conservation aquaculture of threatened and data poor rheophilic cyprinids of the region.

The European catfish Silurus glanis (Linnaeus, 1758) is an expanding apex piscivorous predator whose predation may drive fish harvest rates and fish populations. This study aimed to analyze the relationships between intensive catfish stocking/harvesting and harvest rates of putative catfish prey–three rheophilic fish species: vimba bream Vimba vimba, nase Chondrostoma nasus, and barbel Barbus barbus (Linnaeus, 1758). The GAM (generalized additive model) was used to analyze the relationships between the harvest rate and the stocking intensity rate of the catfish and the three rheophilic fish species. The harvest rates and stocking intensity rates were obtained from mandatory angling logbooks collected from 38,000 individual recreational anglers by the Czech Fishing Union on 176 fishing sites over the years 2005–2017 in central Bohemia and Prague (the Czech Republic). Our results show that a higher intensity of catfish stocking and harvesting resulted in a lower harvest rate of rheophilic fishes. Conversely, the stocking rates of rheophilic fishes were not significantly correlated to their harvest rates. In conclusion, a significant negative relationship was found between the harvest rate and the restocking rates of rheophilic fishes and their predator, suggesting that fisheries managers should not perform intensive stocking of both catfish and rheophilic fishes on the same rivers.

Once abundant in the Nida River, vimba bream (Vimba vimba) was not detected during extensive electrofishing surveys undertaken in the late 1960s, 1990s, or early 2010s. Irrespective, a few angler records of this species suggested that a small population of vimba bream might persist in the Nida River. Finally, several records from 2015, 2016, and 2017 confirmed its presence in this river system and indicated its successful reproduction in the middle reach of the river.

In the present study, the concentration of (potentially toxic element) PTEs in the five fish species from the Caspian Sea (from five coastal areas) was measured and compared. The target hazard quotient (THQ) and total THQ (TTHQ) were calculated using Monte Carlo simulations to determine the non-carcinogenic risk in both children and adults consumers. The highest concentration of PTEs was associated with chromium (Cr) measured in Cyprinus carpio, sampled from Bandar Anzali (1.56 ± 0.14 μg/g dw), and the minimum PTEs level was nickel (Ni) in Vimba from Astara (0.02 ± 0.01 μg/g d w). The rank order for PTEs based on THQ was mercury (Hg) > cadmium (Cd) > lead (Pb)> Ni > tin (Sn) > Total Cr. For adults, the fishes rank order based on TTHQ was: Cyprinus carpio (3.268) > Chelon saliens (2.89) > Rutilus frisii kutum kanesky (2.28) > Oncorhynchus mykis (1.39) > Vimba (0.25); and for children was Cyprinus carpio (15.25) > Chelon saliens (13.47) > Rutilus frisii kutum kanesky (10.63) > Oncorhynchus mykis (6.48) > Vimba (1.16). Overall this study showed that the levels of PTEs in investigated fish species had a potential non-carcinogenic risk for both children and adults (TTHQ>1).

The meso-scale habitat simulation model MesoHABSIM was applied in three Lithuanian lowland rivers to study the effect of low-head hydropower plants (HPPs) on the fish habitats. Stream flow time series on a daily scale for the period 1970–2015 were used to describe flow regime downstream of HPPs for periods before and after their installation. Conditional habitat suitability criteria were developed for 4 species of cyprinid fish, schneider (Alburnoides bipunctatus), dace (Leuciscus leuciscus), roach (Rutilus rutilus) and vimba (Vimba vimba) to simulate their available habitat at different water discharges. Modelling results showed that HPPs have a significant impact on habitat availability in the low flow period in dry years below HPPs due to insufficient released flow. The environmental flow, as prescribed by the Lithuanian national law, is estimated between 80 and 95% exceedance probability of the mean minimum discharge of 30 days. This flow leads to a significant reduction in frequency and duration of available suitable habitats for vimba and schneider during low flow period. The roach habitat is the least affected. The results of habitat modelling are in line with the actual data on the occurrence and relative abundance of considered fish species in the studied river stretches. A general comparison of the relative abundance of modelled fish species in 42 natural river stretches and 20 stretches below the HPPs also showed that the relative abundance of roach is significantly higher, and that of schneider is significantly lower in river sections below the HPPs than the abundance in natural river sections. All results indicate that the current environmental flow does not secure survival of certain fish species. The applicability of the average low flow release during summer could be a plausible alternative to the current environmental flow in order to maintain ecosystem health and services.

An attempt was made to assess the influence of major limiting factors on changes in the vimba population number in the Volgograd Reservoir. According to one hypothesis based on the accessibility of vimba spawning grounds, its population number in the reservoir is already close to the limit. According to another hypothesis considering limitations on the vimba population by food resources, an approximately 15-fold increase in the population number over at least two decades is possible. The above-mentioned hypotheses on the factors limiting increase in the vimba population number in the reservoir, provide different forecasts on the ultimate population number and time necessary for its achievement. The only possible way to verify these hypotheses is to carry out further research.

This study was conducted to complement existing data about the life cycle of Caspian vimba, Vimba vimba (L.), with estimations of age, growth, and mortality rates. To achieve this, 811 specimens were collected between May 2012 and June 2013 at three fisheries catch stations in southwestern regions of the Caspian Sea including Talesh, Bandar Anzali, and Kiashahr. The growth rate in vimba is relatively high at approximately 0.29 year-1 for females and 0.32 year-1 for males. Asymptotic lengths are 245 mm and 233 mm for females and males, respectively. The growth pattern was isometric for both males and females. The overall sex ratio was balanced (1: 0.92). The instantaneous coefficients of total, natural, and fishing mortality were 1.27, 0.4, and 0.8 year, respectively, and the current exploitation ratio was 0.63 year-1. Results showed that the growth rate of males is higher than that of females. Considering the exploitation ratio, it is apparent that the vimba population is experiencing significant legal and illegal exploitation pressure. CORRESPONDING AUTHOR: F. Taridashti [+], J. Imanpour Department of Fisheries, Faculty of Natural Resources University of Guilan, Sowmeh-Sara, P.O. Box. 1144, Iran e-mail: fatemetari88@gmail.com S. Abdolmalaki International Sturgeon Research Institute, Rasht, Guilan, P.O. Box. 41635-3464, Iran M. Hadavi Department of Biology, Faculty of Science, University of Guilan, Rasht, P.O. Box. 41335-19141, Iran

Fish erythrocytes released from erythropoietic sites are immature. During circulation, they increase their own surface, while the cell body and nuclei begin to become more elliptical and less spherical during maturation. The relative abundance of different developmental stages represents an erythron profile which could be a more sensitive indicator of contamination than classic hematological indices. In this study, we analyzed blood smears of the common nase (Chondrostoma nasus) and vimba bream (Vimba vimba) with the main goal to identify the determinants of the developmental stage of erythrocytes. Based on parameters developmental stages, erythrocytes are categorized into immature, intermediate or mature. In this investigation we have used four classification methods: the Two Step Cluster analysis, the K-Means Cluster analysis, and Neural Networks–Multilayer Perceptron and an Ordinal Regression model. Our findings clearly justify that Multilayers Perceptron and OLR models are appropriate to classify the developmental stage of fish erythrocytes in both species.

0000-0003-4599-6780 WOS: 000546985200003 In this study, a total of 1283 samples of five fish species belonging to two families, Cyprinidae and Leuciscidae, were collected from the Lower Sakarya River between June 2017 and May 2018 in or- der to determine some growth parameters.The samples were collected monthly with trammel net, fykenets, and electro shocker. The age of the fish was determined from the scales. The von Berta- lanffy's growth model was calculated Lt = 92.18(1-e(-0.054(t+0.040))) for A. brama , Lt = 69.40(1-e(-0.040(t+0.030))) for B. bjoerkna , Lt = 51.09(1-e(-0.114(t+0.024))) for C. gibelio , Lt = 48.11(1-e(-0.088(t+0.023))) for R. rutilus and Lt = 41.74(1-e(-0.104(t+0.035))) for V. vimba . The phi-prime growth performance index (Phi') value was computed as 2.628, 2.268, 2.474, 2.307 and 2.260 for A. brama, B. bjoerkna, C. gibelio, R. rutilus and V. vimba , respectively. This study provides basic information on some growth parameters of five fish species living in the Lower Sakarya River. The results of this study are useful for fishery managements and stock assessment in the Sakarya River. Mugla Sitki Kocman University, Scientific Research Project OfficeMugla Sitki Kocman University [17/073] This study was funded by Mugla Sitki Kocman University, Scientific Research Project Office with Project number 17/073.

Potamodromous fish are considered important indicators of habitat connectivity in freshwater ecosystems, but they are globally threatened by anthropogenic impacts. Hence, non-invasive techniques are necessary for monitoring during spawning migrations. The use of environmental DNA (eDNA) potentially facilitates these efforts, albeit quantitative examinations of spawning migrations remain so far mostly uncharted. Here, we investigated spawning migrations of Danube bleak, Alburnus mento, and Vimba bream, Vimba vimba, and found a strong correlation between daily visual fish counts and downstream eDNA signals obtained from filtered water samples analysed with digital PCR and end-point PCR coupled with capillary electrophoresis. By accounting for daily discharge fluctuations, it was possible to predict eDNA signal strength from the number of migrating fish: first, the whole spawning reach was taken into account. Second, the model was validated using eDNA signals and fish counts obtained from the upper half of the examined river stretch. Consequently, fish counts and their day-to-day changes could be described via an eDNA-based time series model for the whole migration period. Our findings highlight the capability of eDNA beyond delivering simple presence/absence data towards efficient and informative monitoring of highly dynamic aquatic processes such as spawning migrations of potamodromous fish species.

The European stocks of vimba bream (Vimba vimba) are presently declining, having a "vulnerable" status in some countries. In Romania, there is a lack of scientific studies regarding the species. In order to supplement existing information about this species, specimens of vimba bream were collected from the middle sector of Someș River (Transylvania). Age, length and weight were recorded from 4 sampling points, near gravel quarries. The results show that only young specimens were found. The highest total length value was 22.77 cm, while the highest weight recorded was 121.08 g. Most vimba bream were captured in the first location, where less anthropogenic pressure exists. The populations are in decline in this region because of gravel quarries, among other factors.

The Warta River (795 km long) is the largest, right side tributary of the Odra (Oder) River. The study presents results from one of the best-documented long-term monitoring projects in Poland based on four terms of electrofishing: 1963–66, 1986–88, 1996–98 and 2011–12, conducted in the upper Warta. The Warta River underwent human-induced modifications typical for most European lowland rivers (damming, regulation, water pollution), of which the most destructive for fish was point-source water pollution. In the late 1980s, pollution reached its highest level and stopped increasing as the former political system collapsed and many industrial plants went bankrupt. Surprisingly, recovered fish assemblages were not recorded during the sampling in 1996–98, but in 2011–12. This is why we believe that in large degraded rivers, it takes about 10–20 years before a considerable improvement in fish fauna can be observed. Ichthyofauna recovered to a good status, but was qualitatively different compared to the good status observed in the 1960s. On the one hand, in 2011–12, high species richness and high assemblage diversity were observed, and many species, including seven rheophils, were more common than earlier. On the other hand, the populations of catadromous eel and anadromous vimba have not recovered, and these species were absent in the 2011–12 samples. Because water quality has improved, the most important factor seems to be the impact of the Jeziorsko dam reservoir which is located downstream of the study area and has no fish pass. The above patterns were recognised in this paper with a Kohonen artificial neural network, which is a tool methodically correct for analysing complex non-linear relations. Additionally, indicator species analysis allowed for the identification of significant associations of taxa with specific environmental states and was helpful in determination of ecological statuses of the river stretches. We therefore recommend the combined use of Kohonen artificial neural networks and indicator species analysis in long-term monitoring analyses.

The aim of this study was to determine the exploitation of 7 freshwater species, Freshwater bream ( Abramis brama Linnaeus, 1758), Vimba bream ( Vimba vimba Linnaeus, 1758), Wels catfish ( Silurus glanis Linnaeus, 1758), Roach ( Rutilus rutilus Linnaeus, 1758), European perch ( Perca fluviatilis Linnaeus, 1758), Prussian carp ( Carassius gibelio Bloch, 1782) and White bream ( Blicca bjoerkna Linnaeus, 1758), from Lower Sakarya River, Turkey. Samplings were conducted from June 2017 to May 2018. Length-based estimations were evaluated in FiSAT II software. Total (Z), natural (M), fishing (F curr ) mortality, exploitation rate (E curr ) and CPUEs of all 7 species were determined. Results showed that almost all reference points stayed below the natural and fisheries mortality values. Besides overfishing, pollutants (chemical, physical and biological) and changes in the river morphology may affect the fish populations. Study results could be used for further fisheries management applications.

Accumulation of 17 elements in muscle and liver of common nase and vimba bream, caught between February and May 2016 in the Danube River (1173 river kilometer), were assessed by ICP-OES. The principal component analysis grouped muscle and liver samples based on element concentrations (muscle grouped by higher Ba and Sr values, and liver grouped by higher Al, B, Cd, Cr, Cu, Fe, Mn, and Zn values), but no grouping between the two species was observed. Concentrations of Ba, Cu, Fe, and Zn were significantly higher in muscle, and concentrations of Ba, Cd, Cu, and Mn in liver of common nase, while vimba bream had significantly higher concentrations of Cr and Fe in liver. Common nase has a higher affinity for bioaccumulation of Cu, Fe, and Zn in muscle, while vimba bream has a higher affinity for Al, Cd, and Cr in muscle.

Rheophilic fish species are among the most threatened groups of organisms. There is evidence that anthropogenic activities, such as fish stocking and fishing pressure, could have a significantly negative effect on freshwater fish populations. In addition to this, high population densities of cormorants, Phalacrocorax carbo, (one of the most important avian piscivorous predators in Europe) are also partially driven by anthropogenic activities. The first goal of this study was to estimate the effects of fishery management on fish harvest in three rheophilic fish species: barbel (Barbus barbus), nase (Chondrostoma nasus), and vimba bream (Vimba vimba). The second goal was to estimate the effect of cormorant population density on the harvest of these species. Individual mandatory angling logbooks data were collected on the 22 largest rivers in central Bohemia (Czechia, central Europe) over 13 years. Cormorant density was estimated using bird census data while the diet composition of cormorants was assessed using an analysis of fish diagnostic bones extracted from regurgitated bird pellets. In total, anglers visited the selected fishing areas 3 million times over 13 years and harvested 1 000 tons of fish, of which 4.5 tons were rheophilic species. The fishing effort was the most important driver of fish harvest. Fish stocking and cormorant population density did not significantly affect the fish harvest. However, rheophilic fish species comprised 8.8 % of fish consumed by cormorants (by biomass). In conclusion, fishing pressure was the most important factor affecting the harvest of rheophilic fish. Conversely, the intensity of predation by cormorants was not significantly affecting fish harvest despite their consumption of rheophilic fish. However, there is a possibility that predation pressure of cormorants was evenly distributed among fishing areas.

The reproduction biology of Caspian vimba, Vimba vimba (L.), was investigated on the southwestern coast of the Caspian Sea using 712 fish specimens collected at three fisheries catch stations located in Talesh, Anzali, and Kiashahr over a two-year period from April 2012 through June 2013. Seasonal changes in the gonadosomatic index, gonad histological status, size frequency distribution of oocytes, and the fecundity of the species were studied. The peaks of the gonadosomatic index (GSI) were observed both in females and males in June 2012 and May 2013 indicating the variable peak spawning time of this species. Histological examinations and oocyte frequency distribution patterns showed synchronous oocyte development in the Caspian vimba. Absolute fecundity ranged from 5873 to 35421 eggs. The size at first maturity for females was 120 mm FL. We concluded that the Caspian vimba is a total spawner with variable spawning dependent on environmental factors.

WOS: 000350563400006, The main purpose of this study was to evaluate the gills and gonads of Vimba vimba in terms of fatty acid composition, esterase activity, and esterase band patterns by native-PAGE method. In this context, C16:0 and C18:1n-9 were the most abundant fatty acids in the TLs, NLs, and the PLs fractions of both tissues. EPA (C20:5n-3) and DHA (C22:6n-3) levels were higher in the gills than in the gonads. MUFAs were the main fatty acid groups in the TLs, NLs, and PLs of both tissues. Gills had higher n-3/n-6 ratios when compared with the gonads, with the exception of the PLs. TLs of the gonads had the highest AI and TI values. A concentration of 1 mM Na-taurocholate increased the esterase activity of the gonads. Other chemicals having inhibition and surface active effects resulted in decreases in the esterase activities at concentrations of 1, 5, and 10 mM. In total, nine esterase bands were determined in both tissues. Four bands were shared by both the gills and gonads of V.vimba. These shared bands could be responsible for the similar esterase activities in both tissues. Gills and gonads of V. vimba have substantial amounts of fatty acids and esterase isozymes. More detailed studies are required to understand their industrial and nutritional uses.

In this study we examined the ontogenic development of the digestive tract of Vimba bream (Vimba vimba, Family: Cyprinidae) during the first 60 days of life (hatching to 60 days after hatching [DAH]). Samples of developing Vimba bream were randomly selected at various stages of development: 1–8, 10, 15, 20, 25, 30, 40, 50, and 60 DAH. For the histological and histochemical studies on the development of the alimentary canal, tissue sections prepared from the sampled hatchlings were stained with hematoxylin–eosin and periodic acid–Schiff and observed under a light microscope. The histological structures of both the mouth and esophagus were fully developed at 5 and 7 DAH, respectively. Intestinal differentiation was observed at 2 DAH, while mucosal folds appeared on the intestinal bulb at 7 DAH. At 5 DAH, with the appearance of goblet cells in the epithelium of the mouth, pharynx, and esophagus, the larvae showed secretion activity in these organs. At 6 DAH, secretion was observed in the intestine; at this stage of development, the surface of the gastrointestinal tract was covered in a neutral mucous-like layer of polysaccharide. The histological observations indicate that the early development of the digestive tract in Vimba vimba enables larvae to efficiently ingest and digest exogenous feed very quickly after hatching.

In 2014–2016 complete parasitological autopsy was used to examine 202 individuals of the Kura River estuary fish, belonging to the following 14 species: Caspian common sprat – Clupeonella delicatula caspia, Caspian shad – Alosa caspia caspia, black-backed shad – A. kessleri kessleri, Caspian roach – Rutilus rutilus caspius, kutum – R. frisii kutum, asp – Aspius aspius taeniatus, Kura shemaya – Chalcalburnus chalcoides, Transcaucasian silver bream – Blicca bjoerkna transcaucasica, bream – Abramis brama orientalis, Caspian vimba – Vimba vimba persa, carp – Cyprinus carpio, catfish – Silurus glanis, pike – Sander lucioperca, perch – Perca fluvistilis. As a result of the research there were found following 21 species of parasitic protozoa belonging to 5 phyla, 7 classes, 7 orders and 8 families: flagellates Trypanosoma carassii, Cryptobia borelli, Costia necatrix, coccidia Eimeria carpelli, microsporidium Pleistophora siluri, myxosporeans Myxobolus bliccae, M. bramae, M. cyprini, M. dispar, M. ellipsoides, M. muelleri, M. musculi, M. oviformis, M. pseudodispar, M. rotundus, infusorians Chilodonella hexasticha, Ch. piscicola, Ichthyophthirius multifiliis, Trichodina caspialosae, Ichthyophthirius multifiliis, Trichodina caspialosae, Trichodinella epizootica. The most frequent organ of localization of the parasites were the gills, in their tissues 7 species of myxosporeans, and on their surface 1 species of flagellates and 6 species of infusorians were found. In each of the remaining organs there were noted following numbers of species of parasitic protozoans: in the kidneys – 9 species, in the spleen – 7 species, in the muscles of the body – 6 species, in the skin and bladder – 5 species, in the liver – 4 species, on the surface of fins, in the bloodstream, intestinal walls and gall bladder – 2 species, in the heart, subcutaneous connective tissue, eyes and brain – 1 species. In the composition of protofauna, endoparasites (14 species) significantly prevailed over ectoparasites (7 species), and the forms that develop with a change of hosts (12 species), prevailed over forms that have a simple development cycle (9 species). Most of the parasites are of freshwater origin, so more species of parasites were found in fish caught in the highly desalinated part of the Kura estuary than in areas with more mineralized water. It has been established that, in contrast to ectoparasites, freshwater endoparasites, the infection by which occurs in fresh water, in the body of fish are also transferred to more mineralized sites. Among all discovered protozoa 7 species are the causative agents of fish diseases. However, due to not very high infection of fish, no pathogenic phenomena caused by these parasites were observed.

Summary Gillnet size selectivity was studied for freshwater fish species, based on experimental fishing trials carried out with multimesh gillnets in lentic freshwater systems in Northern Greece. Selectivity estimates were based on a large range of mesh sizes, i.e. more than 10 different mesh sizes ranging from 8 to 90 mm bar length. Results showed that the model, in which both mean and standard deviation of the curve were defined as a linear function of the mesh size, revealed the best fit. For seven (i.e. Αlburnus sp. Volvi, Aspius aspius, Carassius gibelio, Lepomis gibbosus, Pachychilon macedonicum, Squalius prespensis and Vimba melanops) of the 11 studied species and the hybrid (Alburnus belvica × Rutilus prespensis), gillnet selectivity parameters were estimated for the first time, contributing to the evaluation of gillnet fisheries' impacts on fish species populations and consequently to fisheries management and species conservation.