The purpose of this review article is to describe changes in the ichthyofauna of the Aral Sea in the 20th and 21st centuries and comparison of the structure of fish catches in the Aral Sea of the 20th century with those in the Small Aral of the 21st century, as well as a generalization of data on the biology of fish species anew introduced into the Small Aral. In the first half of the 20th century, 20 species lived in the sea, of which cyprinids predominated. After a series of acclimatization measures were carried out in order to enrich the ichthyofauna, 17 new species of fish appeared in the Aral Sea, but the composition of commercial species changed a little. Until 1960, the Aral Sea was in a quasi-stable state. The regression of the Aral Sea began in 1961 and led to the extinction of most species in the ichthyofauna. At the time of the division of the Aral Sea into two reservoirs, only seven species of fish remained in both of them, of which only one species was native. The Small Aral, after dividing the former reservoir into two parts, stabilized its borders. The stabilization of the level of the Small Aral and its freshening led to the return of freshwater fish to the sea. This process had a favorable effect on the size of catches. Currently, the catch volume is about 8000 tons. The future of the ichthyofauna and fish catches depends on what project for the reconstruction of the Small Aral will be chosen. If the option of a singlelevel reservoir will be chosen, the prospects for the fishing industry in the Aral Sea will be more favorable than if the option of a two-level reservoir will be chosen.

Our work is dedicated to the comparison of the quantitative development of meiobenthos during the vegetative season and in winter in the dimictic subpolar Lake Krivoe (Karelia). The winter meiobenthos turned out to be significantly poorer in species composition than the meiobenthos of the vegetative season (13 and 29 species, respectively). Of the 8 meiobenthic groups typical for the lake, Ostracoda and Cladocera were completely absent in winter. An analysis of the proportions of the dominant meiobenthos groups showed that the studied lake fits into the group of typical lakes in the North-West of Russia, and does not belong to the group of polar lakes, as would be expected based on its geographical coordinates. The peculiarity of Lake Krivoe that makes it unique among subpolar lakes is the high biomass in the profundal in winter – 0.14 g/m2, which does not significantly differ from that in the vegetative season – 0.2 g/m2. In the littoral and sublittoral in winter, compared with the vegetative season, there is a significant decrease in meiobenthos biomass from 0.47 g/m2 to 0.03 g/m2 and from 0.05 g/m2 to 0.001 g/m2, respectively. In winter, the largest biomass of meiobenthos is provided by the profundal of the lake – 71.5% of the total biomass of meiobenthos, littoral – 27.25%, and sublittoral zone – 1.2%. In the vegetative season, the opposite picture is observed: in the littoral zone of the lake, meiobenthos makes up 71.5% of the total meiobenthos biomass, in the sublittoral zone – 9.70%, and 18.78% in the profundal zone. The biomass of the winter meiobenthos significantly positively correlates with the meiobenthos biomass in September, r = 0.82 (p < 0.001), and with that in May of the next year, r = 0.56 (p < 0.03). Correlations between meiobenthos biomasses in various months of the vegetative season were non-significant.

В 2022 г. исполнилось 90 лет выдающемуся зоологу и гидробиологу — профессору Владиславу Вильгельмовичу Хлебовичу. Очерк представляет собой краткий обзор его многогранной деятельности и вклада в науку.

Based on published data and studies carried out by the authors over more than 30 years, an analysis of the mollusk fauna of the Aral Sea is made. The species composition of mollusks that lived in the sea during the Holocene is considered and clarified. The main reason for changes in the species composition of this group is shown to have been a decrease or increase in the salinity of the environment associated with changes in the sea level. Long-term changes in the salinity of water, in our opinion, could have become the main reason for the scarcity of the mollusk fauna of the Aral Sea. We assume that the transfer of juvenile mollusks by birds might have played an important role in the replenishment of the fauna with new species. This is probably true for mollusks of the family Cardiidae and Ecrobia grimmi. Another source of replenishment of the fauna of the Aral Sea must have been due to species inhabiting the rivers flowing into the Aral Sea and the surrounding lakes. The process of faunal changes during the last regression of the sea is discussed in detail. The availability of data on the salinity at which the mollusks became extinct makes possible a retrospective evaluation of the estimates of limits of salinity tolerance for the existence of the same species obtained by different methods. The future of the fauna of the mollusks of the Aral Sea is considered in the implementation of different scenarios of sea rehabilitation.

This work is an attempt to trace changes in the fish fauna, their food supply and fish catches in the Small Aral Sea from the beginning of the 20th century to the late 1980s. The purpose of our work is a comparative study of changes in the fishery value of the water reservoir at different stages of its development, including during the last anthropogenic regression. Both literature data and those obtained by the authors in the period 1991–2015 were used. Not only data related to the fauna and fish catches proper, but also data on their food supply, represented mainly by invertebrates, were taken into account. The native ichthyofauna consisted of 20 species of fish, mainly related to benthophages. The biomass of benthos was small — 20 g/m2 due to the significant pressure of fish. The construction of the Tashkent railway was the reason for the emergence of the village of Aralsk in 1905, and the beginning of industrial fishing at sea, as it ensured the export of fish products. The catch of fish in the pre-revolutionary period reached a maximum of 48,300 tons. Planned acclimatization of fish and benthic organisms began to increase the fishery value of the reservoir. Some of them were unsuccessful. The introduction of plankton-eating fish affected not only the zooplankton of the sea, but also its benthic fauna, the abundance and biomass of which decreased. The increase in salinity because of the regression of the water reservoir led to a sharp depletion of the fauna. In the absence of pressure from fish, the biomass of benthic organisms increased by more than 10 times.

Based on the literature and studies carried out by the authors over more than 30 years, an analysis of the fauna of crustaceans of the Aral Sea is presented. The faunal composition, the changes that have taken place since the 1950s, and the relations to the salinity factor are considered. Crustaceans in the Aral Sea make up about one-quarter of the species diversity of Metazoa. They are represented by freshwater, brackish water, and marine species, as well as halophiles from saline continental waters of the arid zone. The first changes in the composition of the crustacean fauna of the Aral Sea started even before its modern regression. They were the result of deliberate, as well as accidental, introductions of a number of initially absent species of invertebrates and fish. Since the 1960s, the main cause has become the rapid change in salinity. As the salinity has increased, the species diversity of the crustaceans has sharply decreased due to extinction, first of freshwater and then of brackish water species. After the level of the Aral Sea fell and it was divided into two parts, the Small Aral and the Large Aral, further evolution of these residual water bodies proceeded in different directions. As a result of the construction of the dam in the former Berg Strait, it became possible to decrease the salinity of the Small Aral Sea and gradually restore the crustacean fauna. The Large Aral has now turned into a hyperhaline water body inhabited by only a few species of crustaceans.

The life cycle of nematode Paramononchus alimovi Tsalolichin on two deepwater stations (St. 2 and St. 18) in Lake Krivoe and the contribution of the long-term climate variability to the dynamics of the quantitative development of this species were investigated. As a result of the research, it was shown that the life cycle of this species in Lake Krivoe is 2–3 months. The temperature conditions of this species existence are stable and close to the temperature optimum for this species. Climatic factors indirectly influence the quantitative development of this species in Lake Krivoe. To analyze the influence of climate on the dynamics of quantitative development of P. alimovi, we calculated the correlation coefficients of the relationship between the average seasonal (May-September) nematode abundance and biomass and indices of the North-Atlantic Oscillation (NAO), arctic oscillation (AO). We found a significant effect of the North Atlantic Oscillation on the quantitative development of nematodes at St.2 for the period July-September (NAO_JAS) with a lag of 2 years, for the period December – March (NAO_DJFM) with a lag of 1 year. For St. 18 a reliable relationship of quantitative development of nematodes with the index for the period March-May (NAO_MAM) without lag is shown. Correlations of climatic indices with benthic biomass with a lag of 1 year and without lag are characteristic of many northern lakes. The maximum income of nutrients should be observed after complete thawing of soils and should be confined to autumn floods. Thus, years with positive index anomalies provide favorable opportunities for the development of phytoplankton in the next year, which is indirectly reflected in the zoobenthos through the trophic chain. Correlation of the NAO index with the values of quantitative development of nematodes in current year is related to the weather preceding the ice disappearance on the lake. Explanation of the obtained two-year lag is associated with another component of the ecosystem – macrozoobenthos. The main component of macrozoobenthos in the depths of the Lake Krivoe is amphipod Monoporeia affinis. This species has 2-year cycle and competes for resources with P. alimovi.

The term 'biological resources' here means a set of organisms that can be used by man directly or indirectly for consumption. They are involved in economic activities and represent an important part of a country's raw material potential. Many other organisms are also subject to rational use and protection. They can be associated with true resource species through interspecific relationships. The Caspian and Aral Seas are continental water bodies, giant saline lakes. Both categories of species are represented in the benthic and pelagic communities of the Caspian and Aral Seas and are involved in human economic activities. The most important biological resource of the Caspian Sea and the Aral Sea is their ichthyofauna, represented by both aboriginal species and species introduced by man in the 20th century. Among invertebrates, the main biological resource of these saline lakes is the brine shrimp Artemia. The physical state of the Caspian as a water body is relatively stable but its biological resources are very seriously affected by irrational use. The Aral Sea since the second half of the 20th century has experienced catastrophic anthropogenic regression, which has led to the almost complete loss of its biological resources due to salinization. However, thanks to efficacious engineering measures, it has now become possible to preserve its northern part (Small Aral) and rehabilitate it, lowering the salinity to its former state. The result has been the restoration of its fish biological resources. In the southern part of Aral (Large Aral), which turned into a group of separated hypersaline reservoirs, the only resource species currently available is the brine shrimp Artemia. The main environmental threats for biological resources of the future Caspian and Aral as well as potential solutions are considered.

The starfish Asterias rubens is one of the most abundant echinoderm species in the White, Barents, North, and Baltic Seas. This species is an important component of marine ecosystems and a model object for certain biological studies, in particular those requiring quantitative estimation of gene expression. As a rule, expression at the transcriptional level is estimated by real-time qPCR using the ΔΔCt method, which allows the comparison of the copy number of target gene transcripts in samples with unknown mRNA/cDNA concentration. Application of this method requires normalization of the results relative to genes with stable expression levels (reference genes). The identification of reference genes is still a challenging task since data of this kind are missing for certain taxa, whereas the use of "standard" endogenous control genes without additional tests might lead to erroneous conclusions. We performed a preliminary analysis of the expression of many housekeeping genes in the pyloric ceca of A. rubens by high-throughput sequencing under normal and heat shock conditions. For one of them, the ubiquitin gene UBA52, low variation of expression (not greater than 2-fold) was shown using real-time qPCR. Tissues of pyloric ceca of normal adults and underyearlings and of adults after heat shock were used. The data obtained suggest that the UBA52 gene may be used as reference for normalization of gene expression at the mRNA level in the starfish A. rubens and probably in closely related species.

Summary The paper describes the comparative analysis of our own experimental data concerning the chaperone activity of 70 kDa heat shock protein (HSP70) in three free-living ciliate species, Paramecium jenningsi, Tetrahymena pyriformis, Paramecium nephridiatum, belonging to the eufreshwater, metafreshwater and euryhaline ecological groups of unicellular organisms. These ciliates revealed different protecting strategies and adaptive potential of their chaperon defensive system regarding to the salinity stress. We infer that the constitutive level of HSP70 content in free-living ciliates reflects the environmental conditions of locations, where from these species originated. Consequently, when evaluating the ecological importance of constitutive HSP70 level in hydrobionts, it is necessary to take into account not only contemporary conditions of their existence, but the chaperone system “memory” as well.

Our own studies of alterations in the level of constitutive heat shock protein of 70 kDa family (Hsp70) in freshwater (Paramecium jenningsi), meta-freshwater (Tetrahymena pyriformis) and curyhaline (P. nephridiatum) ciliates acclimated to salt-water and fresh-water medium were reviewed. It has been shown that the level of constitutive Hsp70 content correlates with the salinity-resistance of ciliate species: in P. jenning i it was lower in freshwater, than in marine water, in euryhaline P. nephridiatum it was higher in freshwater, than in marine water, and was more or less stable in T. pyriformis, the ciliate that occupies intermediate position between two mentioned above species according its salinity-resistance. The ecological importance of constitutive heat shock protein level is discussed in the context of salinity adaptations studies.

ÐÅÇÞÌÅ: Äëÿ îöåíêè àäàïòèâíûõ ñïîñîáíîñòåé áåëîìîðñêîãî ìíîãîùåòèíêîâîãî ÷åðâÿ Nereis pelagica Linnaeus, 1761 ê èçìåíåíèþ ñîëåíîñòè ñðåäû ïðè çàäàííûõ çíà÷åíèÿõ ñîëåíîñòè àêêëèìàöèè îïðåäåëÿëè äèàïàçîí ñîëåíîñòíîé òîëåðàíòíîñòè ê ïîâûøåííîé è ïîíèaeåííîé ñîëåíîñòè.Ïîëó÷åííûå äàííûå áûëè èñïîëüçîâàíû äëÿ ïîñòðîåíèÿ ñîëåíîñòíîãî òîëåðàíòíîãî ïîëèãîíà è îöåíêè ïîòåíöèàëüíîãî ñîëåíîñòíîãî äèàïàçîíà