Electric fish barriers of various systems have long been successfully used to protect fish from entering water intake structures, especially under conditions that make it difficult to use other types of fish protection devices and structures. Strong electric fields created by electric fish barriers can affect the survival, physiological state and injury rate of juvenile and adult fish. At the same time, the sensitivity of fish to such impacts is largely determined by their size. In this regard, we have carried out a complex study to examine the biological safety of electric fields generated by the electronic programmable complex fish-protecting facility of electrical action (EPS IFPEI) on mass fish species from the coastal zone of the Caspian Sea and separate estuaries of its tributary rivers. Behavior and distribution of fish of different size groups (juveniles and adults) at different levels of electric impact from the fish barrier were tested. Survival and injury rates of fish at prolonged maximum voltage of electric fish barrier were evaluated. As a result of the experiments, the modes and parameters of the electric fish barrier (EPS IFPEI) effectively causing behavioral avoidance response in fish were established. Significant differences in survival of individuals from the intact (control) and electrically exposed (experimental) groups of fish were not revealed.

The first data on the structural and functional characteristics of planktonic communities of prokaryotes and viruses in the river and lakes of the October Revolution Island of the Severnaya Zemlya archipelago are presented. High values of the abundance, frequency of dividing cells, and specific growth rate indicated a high activity of prokaryotes during a short period of ice absence both in river and lake aquatic ecosystems. During this period (late July), the abundance of viruses exceeded that of prokaryotes in the river and lakes by 9 and 3 times, respectively. The mortality of prokaryotes as a result of viral lysis reached 34

For the first time, light microscopy has been used to study the parameters of blood cells for the Black Sea sprat (Clupeonella cultriventris Nordmann, 1840) from the Ivankovo Reservoir with trypanosomes in the peripheral blood. A shift in the composition of erythrocytes towards immature cells, lymphopenia, an increase in the proportion of immature granulocytes, and a decrease in the proportion of platelets have been detected. It is noted that fish of this species had not previously been infected with trypanosomes in the Ivankovo Reservoir.

Among the Arctic seas, the largest volume of river runoff (~45% of the total river-water inflow into the Arctic Ocean) enters the Siberian Kara Sea.The viral communities of the Kara Sea are important for the functioning of the marine ecosystem.Studies of virus-prokaryote interactions on the Kara Sea shelf have been conducted only in spring and autumn.Here, we investigated the abundance of free viruses, viruses attached to prokaryotes, and pico-sized detrital particles; the morphology (shape and size) of the viruses, viral infection and virus-mediated mortality of prokaryotes in early summer, i.e., during a seasonal ice melting period and maximum inflow of river-water volumes with high concentrations of dissolved and suspended organic carbon.Seawater samples for microbial analyses were collected across the Kara Sea shelf zone on board the Norilskiy Nickel as a research platform from June 29 to July 15, 2018.Abundances of prokaryotes (range (0.6-25.3) × 10 5 cells mL -1 ) and free viruses (range (10-117) × 10 5 viruses mL -1 ) were correlated (r = 0.63, p = 0.005) with an average virus: prokaryote ratio of 23.9±5.3.The abundance of free viruses and viral-mediated mortality of prokaryotes were significantly higher in early summer than in early spring and autumn.Free viruses with a capsid diameter of 16-304 nm were recorded in the examined water samples.Waters in the Kara Sea shelf contained high concentrations of suspended organic particles 0.25-4.0µm in size (range (0.6-25.3) × 10 5 particles mL -1).The proportions of free viruses, viruses attached to prokaryotes, and viruses attached to pico-sized detrital particles were 89.8±6.0%,2.2±0.6% and 8.0±1.3%, respectively, of the total virioplankton abundance (on average (61.5±6.2) × 10 5 viruses mL -1). Viruses smaller than 60 nm clearly dominated at all studied sites.The majority of free viruses were not tailed.We estimated that an average of 1.4% (range 0.4-3.5%) of the prokaryote community was visibly infected by viruses, suggesting that a significant proportion of prokaryotic secondary production,

Based on the obtained and all available literature data, it has been shown that the abundance of heterotrophic flagellates in the Kara Sea at the end of the season is relatively stable in different years, while in other Arctic seas (East Siberian and Chukchi Seas) the described values of this indicator are 1.5–2 times higher. The indicators of the abundance of heterotrophic nanoflagellates in the bottom water vary to a much lesser extent than in the water column. The abundance of heterotrophic nanoflagellates in the bottom water of the bays of the Novaya Zemlya archipelago is significantly lower than in the same biotopes in the eastern and western parts of the Kara Sea. Most organisms are free-living forms. About a third of the protozoa are associated with detritus particles. The ratio of the biomass of heterotrophic flagellates to the biomass of bacteria more than doubles in the layer of bottom water and in the upper layer of sediments compared to the water column. For the water column of the Kara Sea, the calculated value of grazing of bacterioplankton by flagellates does not exceed 2% of their biomass. The ratio of the eaten biomass of bacterioplankton to the biomass of consumers in most cases decreases with depth.

The distribution of virioplankton, abundance and production, frequency of visibly infected cells of heterotrophic bacteria and autotrophic picocyanobacteria and their virus-induced mortality have been studied in mesotrophic and eutrophic reservoirs of the Upper and Middle Volga (Ivankovo, Uglich, Rybinsk, Gorky, Cheboksary, and Sheksna reservoirs). The abundance of planktonic viruses (VA) is on average by 4.6 ± 1.2 times greater than the abundance of bacterioplankton (BA). The distribution of VA in the Volga reservoirs was largely determined by the distribution of BA and heterotrophic bacterioplankton production (PB). There was a positive correlation between VA and BA and between VA and PB. In addition, BA and VA were both positively correlated with primary production of phytoplankton. Viral particles of 60 to 100 μm in size dominated in the phytoplankton composition. A large number of bacteria and picocyanobacteria with viruses attached to the surface of their cells were found in the reservoirs. Viruses as the most numerous component of plankton make a significant contribution to the formation of the planktonic microbial community biomass. The number of phages inside infected cells of bacteria and picocyanobacteria reached 74‒109 phages/cell. Easily digestible organic matter, which entered the aquatic environment as a result of viral lysis of bacteria and picocyanobacteria, could be an additional source of carbon for living bacteria. The results of long-term studies indicate a significant role of viruses in functioning of planktonic microbial communities in the Volga reservoirs.

The distribution of heterotrophic bacteria, viruses, and heterotrophic nanoflagellates was studied in the shelf waters of the East Siberian Sea along the meridional transect from the Kolyma River delta in September. The production of heterotrophic bacteria and their mortality as a result of protozoan grazing and lysis of viruses were also determined. The patterns of the spatial distribution of microorganisms and viruses varied: the number of bacterioplankton decreased with increasing distance from the Kolyma delta, while, on the contrary, its size and biomass increased to the shelf areas with negative water temperatures. The highest abundance and biomass of virioplankton were recorded at the extreme southern and northern stations of the transect and the abundance and biomass of heterotrophic nanoflagellates increased from the south to the north. The studied shelf waters were characterized by a high concentration of fine-textured detrital particles, and, as a consequence, a relatively large number of viruses attached to detritus. The mortality of heterotrophic bacterioplankton accounted for most of its daily production. Protozoan grazing was the main cause of bacterial mortality that significantly exceeded their mortality due to viral lysis.

The distribution of virioplankton, abundance and production, frequency of visibly infected cells of heterotrophic bacteria and autotrophic picocyanobacteria and their virus-induced mortality have been studied in mesotrophic and eutrophic reservoirs of the Upper and Middle Volga (Ivankovo, Uglich, Rybinsk, Gorky, Cheboksary, and Sheksna reservoirs). The abundance of planktonic viruses (VA) is on average by 4.6 ± 1.2 times greater than the abundance of bacterioplankton (BA). The distribution of VA in the Volga reservoirs was largely determined by the distribution of BA and heterotrophic bacterioplankton production (PB). There was a positive correlation between VA and BA and between VA and PB. In addition, BA and VA were both positively correlated with primary production of phytoplankton. Viral particles of 60 to 100 µm in size dominated in the phytoplankton composition. A large number of bacteria and picocyanobacteria with viruses attached to the surface of their cells were found in the reservoirs. Viruses as the most numerous component of plankton make a significant contribution to the formation of the planktonic microbial community biomass. The number of phages inside infected cells of bacteria and picocyanobacteria reached 74‒109 phages/cell. Easily digestible organic matter, which entered the aquatic environment as a result of viral lysis of bacteria and picocyanobacteria, could be an additional source of carbon for living bacteria. The results of long-term studies indicate a significant role of viruses in functioning of planktonic microbial communities in the Volga reservoirs.

The rise in temperature to anomalously high values for the Middle Volga (27–29°С) in the Cheboksary Reservoir in the summer of 2010 significantly increased (2–14 times) the biomass of some plankton components (phytoplankton, bacterioplankton, protozoans, and zooplankton) and the community as a whole. The total plankton biomass reached a record value of 3 g C/m3 for deep parts in the Upper and Middle Volga. The cyanobacterial bloom of water was observed in most of the reservoir. Differences in the structure of the plankton community and the bacterioplankton-to-phytoplankton production ratio were found between riverine and lacustrine parts of the reservoir. Autotrophic (in the riverine part) and heterotrophic (in the lower lacustrine part) stages of the plankton community development were observed simultaneously in different parts of the reservoir. The functioning of the plankton community in a water temperature that exceeded usual summer heating by almost 9°C led to the deterioration of water quality in the reservoir.

We studied vertical distribution of bacteria and viruses in different layers of the Arctic sea ice drilled at the North Pole. The sampled multi-year ice was characterized by uneven vertical distribution of bacterial abundance. This characteristic varied within the range of 8±1.2 ×103 to 95±2.6 ×103 cells ml-1. The average bacterial abundance was 28±2.9×103 cells ml-1. The layers with the maximal bacterial abundance were located in the intermediate and lower layers of the ice cores. The morphological composition of bacterial population of the multi-year ice was dominated by the cocci cells (63-92%). Bacterial population of the multi-year ice consisted of rather large cells with the mean cell volume of 0.14 μm3. Bacterial biomass varied from 0.5 to 5 mg C m-3 with the mean value 1.57±0.2 mg C m-3. The vertical distribution of bacterial biomass generally followed the pattern of bacterial abundance distribution. The maximal viral abundance was also located in the upper, intermediate and lower layers of the ice. The ratio of viral to bacterial abundance varied from 0.6 to 28, with the mean value 12.5. The average total number of phages attached to bacteria was 6.2 ×103 viral particles ml-1. The fraction of viruses attached to bacteria varied from 0.5 to 20.7%, with the mean value 7.1% of the total viral abundance. The number of bacterial cells with viral particles attached to them varied from 0.7 to 32×103 cells ml-1, with the mean value 8×103 cells ml-1. The number of viral particles located within bacterial cells varied from 2 to 21 particles per a bacterial cell. The minimum and maximum numbers of viruses located on bacterial cells varied from 1 to 6 viral particles per a bacterial cell. The mean viral capsid size varied from 42 to 83 nm. The frequency of visibly infected bacterial cells (FVIC) calculated for the upper, intermediate and lower layers of the ice was 0.92, 1.23 and 0.8% of the total viral abundance, respectively. The overall frequency of infected cells (FIC) calculated for the same layers was 6.3, 8.4 and 0.8% of the viral numbers, respectively, while the viral-mediated mortality of bacteria (VMB) was 7.1, 9.8 and 6.1 %, respectively. The average number of viral particles located within bacterial cells was 7.3 particles per a cell. Our data show that during the study period the rate of viral infection of bacterial cells and the viral-mediated mortality of bacterial cells in the multy-year ice of the North Pole were relatively low.

Проведен анализ вертикального распределения бактерий и вирусов в разных слоях арктического морского льда, отобранного на Северном полюсе. Керны двухлетнего льда характеризовались неравномерным вертикальным распределением бактериальной численности, варьирующей в пределах от 8±1.2×103 до 95±2.6×103 клеток/мл. Слои с максимальным обилием бактерий были расположены в средней и нижней частях кернов. Бактериальная биомасса варьировала от 0.5 до 5 мгС/м3. Соотношение численности вирусов и бактерий варьировало в пределах 0.6–28 при среднем значении 12.5. Среднее общее количество фагов, прикрепленных к бактериям, составляло 6.2×103 вирусных частиц/мл. Количество вирусных частиц, находящихся в бактериальных клетках, менялось от 2 до 21 частицы на одну бактериальную клетку. Частота видимых инфицированных бактериальных клеток, рассчитанная для верхних, средних и нижних слоев льда, составляла 0.92, 1.23 и 0.8% от общей численности бактерий соответственно. Частота инфицированных клеток бактерий, рассчитанная для тех же слоев, составляла соответственно 6.3, 8.4 и 0.8% от числа бактерий, тогда как вирусиндуцированная смертность бактерий составляла 7.1, 9.8 и 6.1% соответственно. Наши данные показывают, что в период исследований уровень вирусной инфекции и вирусиндуцированная смертность бактерий во льдах Северного полюса в целом были относительно низкими.

Trypanosomes are flagellated protozoa; they parasitize in the blood of a wide range of vertebrates and invertebrates, including fish, for which leeches are carriers. The metabolites released by trypanosomes are toxic to the host, cause disruption of homeostasis, which leads to illness and even death. Parasites in fish living in hot climates are the most common and better studied. Trypanosomes were first detected in common bream (Abramis brama L.) from the Uglich Reservoir (Upper Volga) in August 2015. The aim of this work is to study the effect of these parasites on the hematological parameters of the fish. As a control, blood indices of uninfected fish were used. The condition factor of infected fish did not differ from that of healthy fish. There were no significant differences between the two groups of fish in contents of total serum protein and glycemia. This may indicate a low level of bream parasitemia. At the same time, a significant increase in the leukocyte abundance index was detected, which indirectly indicates an increase in the number of these cells in the infected fish compared with the control ones, statistically significant differences were found in the leukogram: the proportion of eosinophils in the diseased fish increased almost 6 times while the relative number of lymphocytes decreased. The pattern of red blood also changed: the proportion of immature erythrocytes increased in the infected fish; a small number of microcytes and amitoses of erythrocytes and differences in the cytometric characteristics of red blood cells were found. The level of hemoglobin significantly decreased. A sharp increase in the content of circulating immune complexes indicates a shift in antigenic homeostasis caused by the presence of parasites. A similarity in the reaction of a number of indicators of the blood system of bream with trypanosomiasis to that of animals of higher systematic groups was revealed. The interpretation of the results obtained during the study of the effect of parasites on the host organism requires consideration of its physiological status and habitat conditions, the stage of the disease and the mechanism of adaptation of the parasite to the host defense system.

The separate and combined effects of chronic 30-day exposure to the herbicide Roundup in a sublethal concentration of 2 μg/L and an increase in water temperature at a rate of 8°C/h on the parameters of red and white blood in juveniles of Amur sleeper Perccottus glenii Dybowski have been studied. The ratio of mature and immature erythrocytes in the peripheral blood do not change under the influence of the studied factors. An increase in temperature after chronic exposure to Roundup leads to a decrease in red blood cell sizes and increase in the share of abnormal cells. Exposure to the herbicide and the rise in water temperature have the opposite effect on the number of amitosis in erythrocytes and the ratio of leucocyte cells; an antagonistic effect is identified under the combined action of the factors. Changes in white blood correspond to a nonspecific stress response; changes in red blood indicate a reduction in compensatory responses to hypoxia.

The abundances of virioplankton and planktonic picocyanobacteria in deep and shallow water sites of Rybinsk Reservoir during the freezing period (water temperature 0.3–0.9°C) varied from (37.1 to 84.1) × 10 6 ((57.3 ± 2.1) × 10 6 , on average) particles/ml and from 13.5 to 75.0 × 10 3 ((48.7 ± 3.4) × 10 3 , on average) cells/ml, respectively. The fraction of picocyanobacteria with viruses attached to their cell surface was 6.5–29.0% (12.0 ± 0.8%, on average). The proportion of visible infected cells was 0.7–7.6% (2.2 ± 0.3%, on average) of the numbers of picocyanobacteria. It is likely that viruses play an important role in the regulation of picocyanobacteria abundance during the freezing period.

The distribution of structural and functional characteristics of virioplankton in the north of the Ob River estuary and the adjacent Kara Sea shelf (between latitudes 71°44′44″ N and 73°45′24″ N) was studied with consideration of the spatial variations in the number (N B) and productivity (P B) of bacteria and water properties (temperature, salinity, density) by analyzing samples taken in September 2013. The number of plankton viruses (N V), the occurrence of visible infected bacteria cells, virus-induced mortality of bacteria, and virioplankton production in the studied region varied within (214−2917) × 103 particles/mL, 0.3−5.6% of NB, 2.2−64.4% of P B, and (6−17248) × 103 particles/(mL day), respectively. These parameters were the highest in water layers with a temperature of +7.3–7.5°C, salinity of 3.75−5.41 psu, and conventional density (στ) of 2.846−4.144. The number of bacterioplankton was (614−822) × 103 cells/mL, and the N V/N B ratio was 1.1−4.5. A large amount of virus particles were attached to bacterial cells and suspended matter. The data testify to the considerable role of viruses in controlling the number and production of heterotrophic bacterioplankton in the interaction zone of river and sea waters.