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 1990s to the present. 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 stabilization of the level of the Small Aral Sea, which followed the construction of the Kokaral dam, greatly changed the situation. The gradual decrease in the salinity of the water reservoir allowed the fish living in the Syr Darya to return to the sea. There are currently 16 species of fish in the sea that can be found in commercial catches.

The Kara-Bogaz-Gol Bay has a high natural potential for cysts of the brine shrimp Artemia parthenogenetica, which can be used in various areas of the national economy. Commercial fishing of the Artemia population of Kara-Bogaz-Gol Bay began in the mid-1990s. As a result, a new potential of the bioresource of cysts on the international market was discovered. Since 2000, there has been a sharp decline in the breeding stock of the Artemia population in the Kara-Bogaz-Gol Bay. By 2002, commercial fishing of Artemia cysts in Kara-Bogaz-Gol Bay was stopped, due to the fact that the brine shrimp population was in a depressed. The main reason was the increase in the salinity of the Kara-Bogaz-Gol Bay due to the accumulation of brine in the strait connecting the Caspian Sea with bay, which prevented the flow of Caspian water into the bay, in volumes sufficient to maintain the salt balance in the Kara-Bogaz-Gol Bay at the optimal level for the development of the Artemia population. Since 2020, there has been a decrease in the level of the Kara-Bogaz-Gol Bay, which continues at the present time. Satellite data show that there are minor accumulations of algae and Artemia cysts in the bay. Minor accumulations of brine shrimp cysts in the bay can be used as a starting potential necessary for inoculation work, after resolving the issue of maintaining the salt balance in the reservoir at a level sufficient for the development of the nutrition of Artemia and its reproduction in natural conditions. To revive the Artemia cysts fishery, a set of measures aimed at improving the hydrological and ecological regimes of the bay has been proposed.

In the Caspian Sea, as in any natural body of water, the distribution and dynamics of the number of fish, including mullet, is due to the combined influence of environmental factors. In the present period of regression of the sea and changes in the level of runoff of the Volga River, salinity plays an important role in the life cycle of all representatives of the ichthyofauna. The article is devoted to the topical issue of the impact of the salt regime on the spatial and quantitative characteristics of the mullet population. The distribution and its relative abundance in 2016 and 2019 observations are presented. The distribution areas are mapped with a detailed description of the features of the formation of concentrations during two contrasting periods: desalination and salinization of the sea. Analyzing the data of trawl catches, it was found that in 2016, when the powerful Volga runoff led to the expansion of desalination zones, the average catch of mullet was 7 copies/an hour of trawling. It is noteworthy that this indicator has grown to 11 copies/an hour of trawling, during the salinization of the Northern Caspian in low-water 2019 Graphical data confirming the presence of a direct correlation between the relative abundance of mullet and increasing salinity gradients are presented. It is shown that for two years the value of the correlation coefficient was 0.74–0.76. Mullet was caught in areas with salinity from 2 to 17%. It was found that the majority of concentrations (68–74%) were formed in marine waters from 8%. In conclusion, it is concluded that the increase in salinity indicators of the northern part of the Caspian Sea has a positive effect on the expansion of the range of mullet.

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.

The purpose of this work is to increase the rate of development and growth of Arctic char juveniles, a valuable promising specy for both commercial cultivation and artificial reproduction. The basis of the new method of the increasing cultivation biotech efficiency is the use the artificially saline biostimulating medium. For maximum stimulation of the juveniles growth rate, they were grown at a commercial farm in table salt solutions of 0.5–1.5‰ concentration, where 2 most important and widely used factors of the same effect were additionally included — optimal temperature and planting density, according to the basic principle of the natural impacts complexity. The maximum weight values (428±23 g) were obtained in a group with pre-sorted leaders of the lowest planting density (27 pd/m3 ) with that compared to more compacted (119±15 g) and control in fresh water (93.8±0.52 g) both in the same planting density (500 pd/m3 ). For the first time, an increase in the growth rate of Arctic char juveniles was observed when using even a slightly saline medium (0.5–1.5‰), below the threshold of critical salinity (4–8‰). The main advantage of growing juveniles in this combined medium — the growth rate increase to 26.97% was revealed, by comparative analysis. The industrial table salt solutions of low concentration are proposed to use in combination with known methods for optimizing the juveniles planting density (as well as temperature regimes, sorting) to accelerate the growth rate of juveniles that comparable to the effect of critical salinity in closed water supply systems of fish farms for yearround rearing.

Artemia cysts are economically significant. One of the components of the reserve is the biomass of artemia cysts submerged to the bottom. 22 hyperhaline lakes of the Altai Territory were studied in 2018–2021. It was found that artemia lived in all the studied lakes, including bisexual populations in 4 lakes, and parthenogenetic populations in 18. The lakes were conditionally divided into 5 groups. 1192 soil samples were selected and processed. The types of sediments were conditionally divided into 6 groups depending on the dominant particles. The dependence of the concentration of bottom artemia cysts on the type of sediments was revealed (r = 0.289, p = 0.001, n = 732). It is determined that the concentration of cysts does not depend on the salinity of the water in the lake, with the same salinity, the density of cysts varies from 0 to several million depending on the type of sediments. The dependence of the concentration of bottom cysts in the summer period on the selected group of lakes was established (r = 0.817, p = 0.1, n = 5). In brine lakes the minimum concentration was observed in spring, in Deep-water and Medium-deep lakes the maximum was observed in summer, in Shallow brine lakes — in autumn. In group of lakes “Shallow, salt precipitates“ and “Drying up in summer” lakes a decrease in the concentration of cysts at the bottom was noted from spring to autumn. The influence of the depth of occurrence on the density of artemia cysts in silt sediments has been studied: in Maloe Yarovoye Lake 63% is in the upper layer, in Kulundinskoye Lake the highest density is in a layer of 5–10 cm, in Bolshoe Yarovoye Lake cysts are evenly distributed in viscous silt at a depth of 5 to 20 cm. The change in the concentration of bottom cysts in autumn and subsequent spring was analyzed to identify the proportion of cysts that have risen from the bottom. Up to 98% of cysts float in Shallow lakes, 4–62% in Deep and Medium-deep lakes.

Salinization of freshwaters is a serious problem leading to a decrease in biodiversity and degradation of aquatic ecosystems. In conditions of climate warming, the toxic effect of salinization can increase. The aim of this study was an experimental assessment of the survival of the pre-larvae of the Eurasian perch Perca fluviatilis under conditions of different concentration of two types of salt (salt mining wastes and sodium chloride), and also under two temperature regimes. We found that under temperature conditions of 8–15 ° C, the mortality of pre-larvae was significantly lower compared to the values obtained with an increase in temperature by 5 °C. The tolerance limit (LC₅₀) under exposition to salts for 24 hours was a mineralization value equal to 9.8 g/l and 8.7 g/l under an exposition of 72 hours. There were no significant differences between the two types of salts — salt mining wastes and sodium chloride in terms of LC₅₀. There were also no significant differences in the time of death of 100 and 50% of the tested prelarvae. At the same time, a higher mortality of pre-larvae was revealed in solution of salt-mining wastes at concentrations of 7 and 8 g/l. At concentrations above 9 g/l, the opposite trend was observed — a greater mortality rate was found in sodium chloride solution. For both types of salts, a greater survival rate of prelarvae was revealed at a salt concentration of 8 g/l compared to a concentration of 7 g/l, which requires more detailed studies. These results are important for understanding the limits of tolerance to salinity in the larval stage of development of one of the most widespread ecologically flexible freshwater fish species. The relevance of the study is determined by current trends in climate change and the increasing level of salinization of boreal freshwaters as a result of salt pollution.