Rainbow trout, or mykiss (Oncorhynchus mykiss), is one of the most popular species used in aquaculture and has been naturalized worldwide, including in the Central Asian Balkhash basin, which has unique aboriginal fish fauna. Both rainbow trout from European farms and wild mykiss from Kamchatka were introduced to some mountain lakes and rivers of the Balkhash basin about 50 years ago. This study investigates the current distribution and life history traits of the alien species and its possible impact on the local fish fauna. This study showed that the rainbow trout occupies various habitats in the Ili River basin: mountain lakes, fast-flowing mountain rivers, and lowland rivers with slow currents and warm water (up to +27 °C). Rainbow trout from European fish farms dominate the mountain Middle Kolsay Lake, while the wild trout from Kamchatka occupies the small Ulken Kokpak River. Both co-occur in the Chilik River. Contrary to that in other regions, the distribution of rainbow trout in the Balkhash basin remained almost the same after their introduction. Broad intrapopulation variability in terms of size, growth rate, and maturation age was revealed, apparently as a result of adaptation to the new environment and intrapopulation competition. In particular, the growth rate has decreased, but life span, surprisingly, has increased as compared to the originally introduced fish. Intrapopulation variation in growth and maturity patterns was also noted. Differences in skin coloration between highland (cold-water) and lowland (warm-water) populations were discovered. The feeding mode of naturalized trout is insectivorous (insect imago), indicating that it occupies its own niche in the local fish communities. The largest population of rainbow trout was recorded in the Lower Kolsay Lake, lowering the population of native fish species, while in other localities, no negative impact on local fish communities was recorded.

The aboriginal ichthyofauna of the Balkhash basin consists mainly of endemic fish species. By the end of the last century, indigenous fish species were driven out of Lake Balkhash and the Alakol Lakes remain the largest refuges of aboriginal fish fauna. Knowledge of regularities of the modern distribution of the indigenous fishes is crucial for biodiversity conservation as well as restoring aquatic ecosystems. The modern diversity of fish species was investigated there in this study. Significant changes for the indigenous and some alien fish distributions were revealed in contrast with earlier known data. Canonical correspondence analysis (CCA) was used to study the relationships between habitat characteristics and species abundance. Water mineralization and maximal observed water temperatures were estimated as the main environmental variables in fish distribution at the local scale. Habitat change leads to fish fauna homogenization as a result of rare species extinction and alien penetration. Growing human population and poor water management make the future of the indigenous fishes unpredictable.

We conducted a study of the modern fish diversity of the Syr Darya River (Aral Sea basin) and its tributaries flowing down from the Karatau Mountains (2007-2023). The physico-chemical parameters at the fish sampling sites (2022-2023) were also studied. As a result of abstraction for irrigation, most tributaries do not reach the main river. The water level, turbidity, salinity, and nitrate content varied unpredictably for fish. A reduction in the diversity of fish has been established both in the main river and in its tributaries. It is most likely that Acipenser nudiventris, Pseudoscaphirhynchus fedtschenkoi, Luciobarbus capito, Aspiolucius esocinus, Capoetobrama kuschakewitschi and Pungitius platygaster aralensis have been extirpated here. The main river is no longer inhabited by Schizothorax intermedius nor the 4 native species from the family Nemacheilidae and Sabanejewia aralensis. In contrast, the Danube bleak Alburnus chalcoides (Güldenstädt 1772) spread much further along the Syr Darya. The reduction in fish diversity has affected the main stream to a greater extent than the tributaries. The fish diversity of the main river consisted of 17 native and 12 alien species, while the tributaries were inhabited by 20 native and 10 alien species. The state of the environment in the basin of the Kazakh section of the Syr Darya River remains unfavorable for local fish species. The ecological degradation of the basin's water bodies requires an integrated approach by biologists, policymakers, and the local community.

The diversity and distribution of fish in the water bodies of the Black Irtysh basin was studied in connection with six abiotic environmental parameters (surface flow velocity, width and depth of rivers, connection with the main river, and bottom and maximum temperature). The current species diversity of fish consists of 29 native and 11 alien species. The diversity of right and left tributaries varies greatly as a result of differences in abiotic parameters. The presence of a hydrological connection of reservoirs by itself does not guarantee the distribution of species throughout the basin. Rare indigenous Siberian Taimen Hucho taimen and Markakol Lenok Brachymystax savinovi were regularly found in the right tributaries of the Irtysh River and Lake Markakol, respectively. New fish species to the Kazakh section of the Black Irtysh River have been discovered: Tibetan stone loach Triplophysa stolickai, Severtsov’s loach Triplophysa sewerzowi and alien fish species as asp Leuciscus aspius, Chinese false gudgeon Abbottina rivularis, sunbleak Leucaspius delinetaus, and Misgurnus sp.

Human made ecological crisis in the basin of Aral Sea has gone strong negative impact to the native fish fauna. The tributaries of the Syrdarya River turned out to be natural shelters for many non-commercial fish species. The objectives of our study were to study morphological variability and assess the state of the dace population inhabiting the Shayan River. Fish for study were caught in 2013 and 2020. Based on the analysis of external signs, the belonging of the fish to the Zeravshan dace species Leuciscus lehmanni Brandt, 1852 was established. Morphological and biological analyzes of fish were carried out according to the widely used method. The variability of 32 plastic and 18 counting traits, size and weight indicators, fatness, fat content, growth and food objects was studied. Differences in the appearance of individuals may be the result of the implementation of different life strategies in a heterogeneous environmental conditions. For the first time, data on morphological variability, growth and nutrition of the Zeravshan dace were obtained for the water bodies of the Republic of Kazakhstan. In the samples of 2013 and 2020, individuals of different ages were represented. The limits of body size variability coincide, which indicates sufficient conditions for reproduction and existence. In 2013, the sample was dominated by larger individuals, fatness, intestinal filling and fat content were higher than in 2020. Food objects do not change over the years. The intestines of fish from both samples contain detritus, green algae, aquatic insect larvae, and adults of terrestrial insects (Hymenoptera and Diptera). In 2020, some deterioration of feeding happened, which led to a decrease in the reserves of abdominal fat and body condition coefficients of fish. Also in 2020, the violation of the homeostasis of individual development increased. Key words: Zeravshan dace, Leuciscus lehmanni, морфология, биология, изменчивость, Сырдарьинский бассейн, Каратау.

Мақалада 2024 жылы жүргізілген ихтиологиялық зерттеулердің деректері негізінде Қапшағай су қоймасында қаракөз популяциясының құрылымдық сипаттамалары, оның ішінде жастық құрамы, ұзындық-салмақтық көрсеткіштері және жыныстық құрылымы қарастырылған. Ауланған даралардың ұзындық мәндері 89-323 мм аралығында ауытқыса, популяциясы бойынша орташа ұзындығы 193 мм құрады. Үлкен салмағы бойынша 11-622 г аралығында ауытқып, орташа көрсеткіші 163 г сәйкес келді. Зерттеу нәтижелеріне сәйкес қаракөз балықтарының жастық қатары 2-8 жас аралығын құраса, олардың 4-6 жастағы дараларының үлесі басым болды. Ұзындық құрамы бойынша модальды класты 150-199 және 200-249 мм ұзындықтағы даралар құраса, салмақтық құрылымы тиісінше 120-179 және 180-239 г аралығындағы даралардың үлесіне тиесілі болды. Аталған сипаттамалар қаракөз балықтарының 30 мм ұяшықты ғылыми ауларға жиі түсуімен де расталады. Кейінгі жылдары аталған су қоймада қаракөз популяциясының құрылымдық көрсеткіштері жоғарылағаны байқалады. Ғылыми аулардың талдау нәтижесіне сәйкес көктемнен күзге қарай қаракөз балықтарының саны жоғарылайды. Интерполяциялық әдіс бойынша қаракөз популяциясының кеңістіктегі маусымдық таралу динамикасы анықталды. Көктем айларында қаракөз популяциясының кеңістіктегі таралуы Қапшағай су қоймасының оң жағалау акваториясында байқалса, ал жаз және күз мезгілдерінде олардың шоғырлануы сол жағалау акваториясының өзен сағалары маңында болатындығы анықталды. Балықтардың кеңістіктегі маусымдық таралу ерекшелігі де шоғырланған аймақтардағы қоректік базасының жоғары деңгейімен және де басқа да абиотикалық факторламен байланысты болуы ықтимал.