The study of planktonic animals of the Caspian Sea is topical and, during the last centuries, has brought and continues to bring new results. This is an inevitable process attributed to the introduction of non-indigenous predatory representatives of zooplankton by ballast water of ships. During the study period, the zooplankton of the Middle Caspian Sea was represented by 13 taxa and consisted mainly of non-indigenous species typical of the Palearctic region. Native fauna was represented by three species—cladoceran Evadne anonyx, Podonevadne camptonyx, and copepod Halicyclops sarsi during the study period. The quantitative variables of zooplankton did not reach a high level in May 2020 and 2021 compared to the data of previous years. Cladocerans Podonevadne camptonyx, copepods Acartia tonsa, and larvae of Cirripedia dominated in 2020. By 2021, the dominant species of last year had been replaced by the cladoceran Evadne nordmanni. One-way ANOVA analysis detected significant differences in the quantitative variables of cladocerans and copepods between different years of zooplankton study. The decreasing abundance, biomass, and alteration of the dominant zooplankton species in the Middle Caspian Sea during the study period may be associated with the feeding type of predator species and a slight elevation of water salinity.

The data on hosts of Ellobiopsis in Central Asia waterbodies are nearly non-existent. All research in this direction was conducted in other regions (Europe and Brazil). Parasitological studies were carried out in different seasons in the North and Middle Caspian Sea. Twenty-one taxa were registered in zooplankton, and only dominants of community calanoids Acartia (Acanthacartia) tonsa and Calanipeda aquaedulcis were infected with Ellobiopsis sp. Calanoida C. aquaedulcis was reported for the first time as a host for Ellobiopsis. The number of parasites per host was equal to one. The body length of parasites varied from 0.10 to 0.80 mm. The highest infection degree was recorded in C. aquaedulcis (5.71%), and it varied from 2.61% to 3.35% in Acartia. The individuals in the juvenile developmental stages were infected in Calanipeda, while in Acartia, individuals in all developmental stages were vulnerable to infection. The infected calanids had reduced body lengths. The findings suggest the possible influence of Ellobiopsis sp. on quantitative variables of hosts in the Middle Caspian, especially on biomass, by reducing the body sizes of hosts. However, no effect on the abundance and biomass of the host and the structure of the zooplankton of the North Caspian Sea has been detected.

Алғышарттар мен мақсат. Мақалада Қапшағай суқоймасында тіршілік ететін көксерке популяциясының биологиялық көрсеткіштері, морфологиялық талдауы, абсолютті жеке тұқымдылығы (бұдан әрі - АЖТ), жастық құрамы мен кездесу жиілігі, ауланған ау көздеріне қатысты пайыздық көрсеткіштері, суқойма бойынша кеңістікте таралуы берілген. Материалдар мен әдістер. Мәліметтер Қапшағай суқоймасында жиналды және өңдеу жұмыстары «Балық шаруашылығы ғылыми-зерттеу орталығы» ЖШС ихтиология зертханасына жүргізілді. Морфологиялық талдауы Алакөл көліндегі көксеркемен салыстырмалы түрде, ал ұқсастығы кластерлік анализ негізінде жүргізілді. Нәтижелер. Алынған мәліметтерге сүйенсек, аулауда 2 және 4 жас аралығындағы көксерке дарақтарының басым екенін көрсетеді (79,0%), аулау көрсеткіші бойынша көксеркенің ау көзі 30-40 мм ауға ең көп ауланғанын (50,8%) байқауға болады. Көксеркелердің кеңістікте таралуы бойынша алынған нәтижелер көрсеткендей, олар суқоймаға кеңінен таралған. Абсолютті жеке тұқымдылығының мәліметтері жасына қарай тұқымдылығы артатынын көрсетеді, 2024 ж. зерттеу кезінде көксеркенің АЖТ 309,0 мыңнан 801,3 мыңға дейін жеткен. Қорытынды. Жүргізілген зерттеулер нәтижесінде Қапшағай су қоймасындағы көксерке популяциясының жағдайы қанағаттанарлық екені анықталды. Ауланған көксеркелердің жастық құрамы 1-ден 11 жасқа дейiн болды, оның iшiнде 2-ден 4 жасқа дейiнгi жастағы дарақтар басым (79,0%), ал аулауда ересек дарақтардың үлесi аз, шамамен 0,2-9,2%. Фултон бойынша қоңдылық коэффициенті 0,83-2,73 аралығында болды. Балықтардың жасынның ұлғайғанына қарай абсолюттiк жеке тұқымдылығы артады. Зерттеу нәтижелеріне сәйкес көктемгі, жазғы және күзгі кезеңдерде көксерке Қапшағай суқоймасы бойынша кеңінен таралған, бұл су айдынның көксеркенің өсуі мен дамуы үшін қолайлы екенін көрсетеді.

The article presents the results of research work on the creation of a replenishment-breeding herd of Siberian sturgeon. The research work was carried out in the conditions of closed system water supply (emergency situations) at" educational and scientificcomplex of experimental industrial production of aquaculture " LLP. The hydrochemical state of the water of the emergency situations basins was analyzed. The conditions of keeping in the breeding herd (Tau) were studied, the technological equipment of theTSS was evaluated and a morphological analysis of individuals was carried out, as well as the article analyzed the biological indicators of fish breeding of individuals and spring Fry of Siberian sturgeon, age and quantitative composition of Siberian sturgeon. As a result, the results of the morphometric study show that the tendency to increase the coefficient of belching in adult individuals of Siberian sturgeon, as well as the parameters of relative body capture of Siberian sturgeon, is 5.3% higher than in age groups. In the conditions of fish farms, the conditions for the formation of the Tau of Siberian sturgeon met regulatory requirements, and the growth observed during the year also met the standard. An important issue in breeding in commercial farms and reproduction centers is the Prevention of inbreeding. When breeding Sturgeon, as a rule, a small number of broodbugs or only a few pairs are used, which often leads to inbreeding and loss of natural polymorphism. In order to avoid it, it is necessary to use at least 20 seed pairs when planting a female herd and further in the process of its reproduction. For this purpose, the structure of TAS should provide the possibility of industrial reflectivity

The topicality of the study lies in the high natural and economic significance of Lake Alakol, as well as the increasing anthropogenic load affecting its ecological state. Monitoring zooplankton structural variables is important because structure alterations often reflect the general ecological state of the waterbody, including the degree of eutrophication, the level of anthropogenic load, and the stability of ecosystem processes. It is necessary to obtain preliminary information on the current state of zooplankton communities to ensure the informativeness and objectivity of monitoring. Therefore, the first and essential stage is the study of the dynamics of key structural variables. This is the primary goal of this study. Archival data from LLP «Fisheries Research and Production Center» were used to analyze the taxonomic composition, abundance, biomass, and Shannon index for the period 2020-2024. The latter was collected during the calculations for the fish food supply and during the preparation of biological justifications. The similarity of the taxonomic composition of zooplankton in different years was assessed by using Bray-Curtis cluster analysis. High taxonomic diversity (94 taxa) was recorded. Cluster analysis revealed interannual differences in zooplankton taxonomic composition with stability within the year. Significant changes were recorded in 2024. The environmental factors should be the reasonfor these alterations. Interannual alterations in abundance and biomass and the Shannon index in 2024 are probably associated with trophic factors. Rotifers, cladocerans, and copepods were the dominants. It was revealed that the structure of zooplankton is formed under the influence of natural (seasonal temperature fluctuations) and external factors, including trophic ones. The stability of communities is ensured by eurythermal and ecologically plastic species

The bream (Abramis brama orientalis) ranks second in abundance and biomass among fish in the Kazakh sector of the northern part of the Caspian Sea, second only to the common sprat (Clupeonella cultriventris). The annual catch of oriental bream in this region is about 1,500 tons. The study of the commercial population structure and the distribution of stocks of this fish is particularly important in the context of ensuring food security in the Republic of Kazakhstan. This article presents data on the distribution of bream, occurrence in scientific catches, as well as on the population structure of the eastern bream. Both qualitative and quantitative variables of the species for the period 2012-2022 are analyzed. According to the results of both net and trawl catches, the largest numbers of eastern bream were recorded in the areas adjacent to the mouthwaters of the Kigash and Zhaiyk rivers. A particularly high density was observed in the water area adjacent to the mouth of the Zhaiyk River, where the number of bream exceeded 51 specimens/trawl. Significant concentrations of the species were also observed in the central part of the studied water area, where the density reached 118.5 specimens/ha. The results of net fishing in autumn 2022 generally confirmed the data from the trawl survey: a quantitative predominance of bream was recorded in the northwestern part of the water area, where its relative abundance reached 62 specimens per set-up