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To establish the causes and consequences of changes in the relief of the southern Astrakhan region in the period 1900–1970.Comparison of cartographic materials of past years with data in recent satellite remote sensing images. The materials were superimposed on a geoformation program: then the hydrological elements of the relief and the Baer hills were outlined and measured for the purpose of quantitative and qualitative analysis of changes in the territory (before and after reclamation works and the currently existing relief).The analysis of the materials revealed a significant transformation of the relief, which has served as an impetus for the development of a semidesert zone in this area.The work carried out revealed the anthropogenic impact on the relief through which most of the territory was subject to drainage as a result of reclamation works to increase in arable land.

Aim. Analysis of the distribution and status of ctenophores Вeroe ovata and Mnemiopsis leidyi, and assessment of the parameters of their interaction in the Middle Caspian Sea.Material and Methods. The material was obtained in the western and eastern parts of the Middle Caspian Sea in September–October 2022. Large ctenophores were collected using a big cone plankton net with a 0.5 m2 opening and a 500 μm, mesh size. The number and size of large ctenophores were determined immediately after collection, larvae and eggs were counted in samples fixed with formalin to a final concentration of 4%. Zooplankton samples were collected by the Juday plankton net (0.1 m2 opening, 180 μm mesh size).Results. In September‐October 2022, a developed population of Вeroe ovata with active reproduction was recorded in the waters of the Middle Caspian Sea. The habitat area of B. ovata has significantly expanded to the north compared to 2021. Complete suppression of the Mnemiopsis population by the Beroe was observed on most of the western and eastern shelf, as well. The total number of Beroe reached 48 ind/m2, biomass – 12 g/m2. Single large individuals were found in the north of the Middle Caspian Sea at salinity 5.7 psu. The structure of mesozooplankton was still dominated by the small copepod Acartia tonsa.Conclusion. New data indicate the active development of the Вeroe ovata in the Caspian Sea, which presents a fundamental challenge for the restoration of the Caspian ecosystem. The progressive adaptation of Beroe to the conditions of the Caspian Sea has led to its expansion to the north of the Middle Caspian Sea in areas with low salinity. A complete suppression of the M. Leidyi population by the new alien noted on most of the shelf indicates an increase in its pressure on the Mnemiopsis population compared to the corresponding period of 2021.

Aim. The aim of the study is to analyze the current state of artificial reproduction of the Caspian sturgeon and to identify the problems of reducing efficiency and ways to solve them.Discussion. The current critical state of the Caspian sturgeon, which accounts for up to 90% of the world's related resources, is of concern to the entire community, due to the threat of extinction of these relic individuals on the planet. This can be prevented by increasing the efficiency of reproduction. However, natural reproduction is practically reduced to zero, so the real and only possible solution is artificial reproduction. This analytical review presents five tasks, the successful solution of which will improve the current state of artificial reproduction in the Volga‐Caspian basin. The main task is the provision of fish breeding processes with producers, which, in the absence of fish of natural generation, are derived from brood stocks. Of particular concern is the threatened state of the Caspian beluga and stellate sturgeon. It is necessary to increase the release of their juveniles, for which financial stimulation of this activity is necessary. It is necessary to move more actively to the release of juveniles of an enlarged (7‐10 g) size and their export to feeding places in the waters of the Northern Caspian, which will contribute to an increase in fishing return.Conclusion. It is necessary to increase funding for research into the reproductive function of females and for artificial generation, as well as for the maintenance of production herds – a golden fund for restoring natural reserves. The attention of all the Caspian states should be drawn to the intensification of activities for the artificial reproduction of these unique fish species in the Caspian basin.

Aim. This study was an attempt by the authors to identify the impact of oil production in the Caspian Sea on the quality of waters surrounding oil and gas-production platforms.Material and Methods. In 2018, by order of the Committee for Forestry and Wildlife of the Ministry of Agriculture of the Republic of Kazakhstan, Kazekoproekt carried out comprehensive marine research to assess the state of biological resources in the eastern part of the Caspian Sea. All studies were carried out according to standard methods accepted in international practice. Samples were collected in summer (July-August) 2018 and autumn (September) 2018.Results. An analysis of the materials of environmental studies carried out in the water area of the eastern part of the Caspian Sea in 2018 established the absence of biogenic concentrations in sea water in excess of the standard indicators. It was found that in the waters surrounding several stations in summer and autumn, concentrations of oil products were exceeded. The concentrations of pesticides in the waters of the northern Caspian Sea recorded in 2018 were not detected.Conclusion. It was found that in the eastern part of the Caspian Sea in 2018 there was no concentration of biogenic elements in sea water above the standard indicators. Of the heavy metals, an excess of maximum permissible concentrations was found only at one station - of copper in the summer over 159 sq. m and in the autumn over 121 sq. m. Of particular concern is the fact that at several stations in summer and autumn excessive concentrations of petroleum products were recorded. The concentrations of pesticides in the waters of the northern Caspian Sea recorded in 2018 were not detected.

Aim. Analysis of the first data regarding the arrival of the predatory ctenophore Beroe cf. ovata in the Caspian Sea and assessment of possible effects of its introduction for the Caspian ecosystem.Material and Methods. The material was obtained in the deep-water region of the western shelf of the middle Caspian Sea in the first ten days of October 2020. Zooplankton samples were collected using a Juday plankton net (0.1 m2 opening, 180 μm mesh size). Large ctenophores were collected using a big cone plankton net (CB) with a 0.5 m2 opening, 500 μm mesh size. Samples were taken at five stations in the 0-40 m layer. Combs larger than 5 mm were counted and measured on board the ship. The number and size of small ctenophores, larvae and eggs were determined in zooplankton samples fixed with formalin to a final concentration of 4%.Results. The presence of a new alien Beroe cf. ovata was recorded in the Dagestan shelf waters of the Caspian Sea in the beginning of October 2020. The average number of Beroe cf. ovata for five stations was 22 ind/m2 and the biomass was 6.15 g/m2. Larvae and small individuals from 5 to 20 mm in size predominated. Mnemiopsis leidyi was absent in the area investigated. The structure of mesozooplankton was dominated by the small copepod Acartia tonsa, which accounted for 92% of the zooplankton community and 78% of its biomass.Conclusion. The size structure of the B. ovata population with a predominance of larvae and small individuals indicates a recently completed breeding cycle and adaptation of the ctenophore to the conditions of the Caspian Sea. The first impacts of the new invasive ctenophore on the population of M. leidyi were demonstrated. This event may be the beginning of a new stage in the evolution of the Caspian Sea ecosystem and the restoration of its bio resources affected by the invasion of Mnemiopsis leidyi. The structure of mesozooplankton with total dominance, in abundance and biomass, of the small copepod Acartia tonsa did not differ from that in the previous period, indicating that the Caspian zoocenosis did not respond to the short-term reduction of the impact of M. leidyi. A brief analysis of the history of the introduction of ctenophores to the Black and Caspian Seas is presented and their impact on ecosystems and biological resources of these seas is studied. Based on longterm observations of the invasive ctenophores' interactions in the Black Sea, the possible outcomes of the penetration of Beroe cf. ovata in the Caspian Sea are discussed.

Aim. Analysis of new data on populations of invasive ctenopfores Вeroe ovata and Mnemiopsis leidyi in the Caspian Sea and assessment of adaptation of B. ovata to new habitat conditions.Material and methods. The data was obtained in the Dagestan sector of the Middle Caspian Sea in September‐November 2021. Ctenophores and zooplankton were collected by a big cone plankton net (BC) with a 0.5 m2 opening and a Juday plankton net (0.1 m2 opening). Small ctenophores, eggs and zooplankton content were determined in samples fixed with formaldehyde to a final concentration of 4%.Results. In September‐October 2021, the Вeroe ovata were detected in the shelf waters of Dagestan. The total number of ctenophores reached 32 ind/m2, biomass – 10 g/m2. Individuals up to 35 mm in size were recorded. The abundance of M. leidyi in areas where B. ovata was found 3‐10 times less often than in areas where it was absent. The habitat of Вeroe ovata was limited to the southern part of the Dagestan shelf and a salinity range of 7.1‐5.5 psu.Conclusion. In 2021, new data was obtained on the Вeroe ovata in the Caspian Sea. The detection of B. ovata in the Caspian Sea in 2021 indicates that the ctenophore overcame winter conditions of the Caspian Sea. The fact determines the further evolution of the Caspian Sea ecosystem. The parameters of the impact of the new alien on the population of M. leidyi were recorded. An analysis of B. ovata distribution in the waters of the Dagestan shelf depending on environmental conditions was carried out.

Aim. To analyze the results of ichthyological monitoring in order to identify the role of an invasive fish species, Pseudorasbora parva – known in Russia as the Amur Chebachok – in the ichthyological community of the River Don estuary littoral and delta. Material and Methods. Research work was carried out in the prodelta and estuarine watercourses of the Don delta in the period 2007‐2017. To catch the fish, we used bimtral, drag nets, gill nets and other fishing gear. Standard methods were applied to process ichthyological material. A total of 902 specimens of the Amur chebachok were examined. Results. The general characteristics of the invasive species from watercourses of the delta and from Taganrog Bay are given. Its role in the formation of ichthyofauna and its relationship with native species in new habitats has been determined. Dimensionmass indicators and other biological parameters of the species are given. Conclusion. The linear structure of the local population of the Amur chebachok consists of different size groupings corresponding to certain ages. The process of acclimatization of the Amur chebachok in the Don delta is associated with certain interactions with elements of the local biocenosis. It was proved that when there is a high number, both in pond farms and in natural water bodies, the species is an acute food competitor to juveniles of both farmed or local fish. Its rapid spread is due to the high survival rate of offspring, high environmental plasticity, rapid growth, short puberty and the migratory activity of larvae and fry.

Aim. The aim is to study the technological processes of obtaining Bester caviar in the unconventional autumn-winter period.Methods. Extraction of caviar was carried out antemortem by the pillow method cutting the oviducts. The scheme of gonadotropic stimulation for all Bester females was the same: preliminary surfagon injection at the rate of 0.5 mkg/kg, while an acceptable dose of injection is 2.5 mkg per kilogram of fish weight. The object of the research was the female bester (Acipenser nikoljukini) grown in ponds at the age of 12-13 years with the polarization rate of 7-9, the caviar of which was extracted for the third time. The mass of fish and the yield of eggs were determined by the method of Pravdina I.F. The studies were performed in 4 experimental and 1 control variants.Results. We studied the possibility of extracting the caviar of the Bester females (Acipenser nikoljukini) inhabiting the ponds at the natural water temperature in the unconventional autumnwinter period. It is shown that the hybrid form of sturgeon fishes, here, the female bester, can spawn without gradual withdrawal to spawning temperature regime and without prior exposure in these conditions in contrast to the recommendations adopted in sturgeon breeding.Conclusion. We established the possibility of obtaining and producing fresh caviar of sturgeon fishes, especially when the demand increases during the pre-New Year holidays.

Aim. The aim of the study was an attempt to expand on the findings about the structure of the anterior part of the mid-intestine of three species of carp fish: Rutelus frisii kutum (Kamenski), Abramis brama orientalis and Ciprinus caprio (Linne) in connection with the feeding habits in the changed conditions of the western coast of the Middle Caspian sea. Studies of the digestive tract can extend the idea of the specifics of the mid-intestine structure due to the feeding of fish in certain environmental conditions of habitat.Methods. Investigations of the digestive tract were carried out, guided by the "Methodological manual" by I.V. Verigina.Findings and discussion. It is shown that in the anatomical and histological structure of the middle intestine was affected by the feeding habits of these types of fish; feeding upon small and soft invertebrates leads to a relatively simple structure of the intestinal wall: mucous layer covers a small part of the total thickness of the wall; there are no collagen structures that perform the function of the mechanical frame and capsules around blood vessels.Conclusion. Simplification of the digestive system emphasizes adaptive capacity appearing in periodic fluctuation of sea water level. The absence of food of a bigger size in the diet of fish results in a relatively simple anatomical and histological structure of the mid-intestine wall. None of the species under study has a differentiated stomach; instead its role is taken by an expanded portion of the fore intestine, similar is the microstructure of the middle part of the intestines of all three species.

Formation of genetic structure of populations of some breeds of sheep of the North Caucasus on antigenes of blood types under the influence of ecological factors of a place of cultivation and a heredity of the initial breeds used in the course of their deducing is considered. The index of genetic similarity between these populations is defined.

Fish reproduction research showed that the change of existence conditions changes the character of sexual cell growth changes. Evident changes in the duration of protoplasmatic growth are observed as well as the asynchronism degree of sexual cells and their development rate during annual period.

The ecology of the reproduction of the mullets (Mugil auratus) under conditions of Daghestan part of the Middle Caspian Sea has been studied. The superiority of the Caspian mullets over the Black Sean ones has been registered on many biological and economic factors, such as a rate of growth, age of the maturation, fertility and fatness.

The main aim of the article is to study the reproduction and study of gametogenesis (ovo-and spermatogenesis) of many valuable as commercial and of yet not covered by the fishery of species of fishes for various reasons from different taxonomic groups with a different biology. The study of gametogenesis of representatives of different ecological groups (freshwater, marine) allowed not only to establish the regularities, but also reveal features of their proceeding in an ecological conditions of water bodies that have changed due to human influence, and also to note the adaptive changes and to correlate processes occurring in different levels of life.

The effect of CdCI2 (0.25 mg /l) on the proteolytic enzyme activities of the carp tissue are studied. The results confirm the involvement of cathepsin D and neutral protease in the development of the organism's response to the action of cadmium ions.

All the ovogenesis and sex cycles peculiarities of the studied fishes are species-specific with biology particularity of different fishes including their reproductions. The research showed that the changes caused by different anthropogenic factors often change the whole process of gametogenesis thereby the character and fish reproduction intensity in the ecologically changed conditions.

The article is devoted to the state-of-the-art review of materials of researches on a biodiversity and biological resources of Dagestan part Pre-Caspiy. This unique area of Caspian sea consisting its high biodiversity, owing to presence of the powerful rivers (Terek, Sulak and Samur) and gulfs (Kizlyarskiy, Agrahanskiy), creating optimum modes for development sturgeon and herring, and also convenient rookeries of a seal. All these unique natural creations are subject to strong destruction from excessive anthropogenous press.For their preservation and the further development the purposeful nature protection policy with all following questions should be carried out.

There is described a new genus and species - Gasterosteus Aculeatus for the Dagestan part of the Middle Caspian from the genus Gasterosteus species Aculeatus, which differs from other kinds of family Gasterosteidae by presence of three needles on the back part of the body and by some ecological features. This species is well enough described in other southern reservoirs. In comparison of external attributes of the three-needle stickle-back of the Caspian and other southern reservoirs no special differences are revealed.