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.

The objects of study are the territory of the districts of the West Kazakhstan region of the Republic of Kazakhstan adjacent to the Kapustin Yar test site: Bokeyordinsky, Zhangalinsky, Zhanibeksky, Kaztalovsky, Akzhayiksky and Syrymsky. The purpose of the work is to conduct a radioecological survey of contaminated areas and to study the content of pollutants in environmental objects, biota (rodents, fish and biosubstrates of domestic animals) by physicochemical methods to assess the risk of the landfill’s impact on biota and humans. This paper presents the results of expeditionary and laboratory research on the pollution of environmental objects in the areas adjacent to the landfill. Indicators of the gamma-survey of the levels of radiation background of the surveyed territories as wellas data on pollution of soil, surface and ground waters, dominant forms of plants, biosubstrates (hair of domestic animals: camel, horse, cow) are given. The generally accepted research methods were used: standard sampling me thods, radiological, atomic adsorption spectrophotometry, cytogenetic (micronucleus) method. A reconnaissance and radioecological examination of environmental objects was carried out using analytical methods, which made it possible to determine the quantitative content of toxic components, the content of priority pollutants and radioactive isotopes. It has been established that the values of the volumetric activity of natural and man-made radionuclides in soil samples, drinking water and biosubstrates (pet hair, human peripheral blood samples) from settlements correspond to the value of the control level for this region. The measurements of radiation activity by gamma radiation showed that along the perimeter of the surveyed territory of the test site and in nearby settlements the radiation level is in the range of 0.06–0.014 μSv/h. A slight excess of the level of radioactivity persists in the area near the fall of missiles in the Bokeyordin region. The investigated regions are characterized by an insignificant level of background radiation, the average DER value for the regions as a whole is 0.14 μSv/h. The absolute maximum, 0.73 μSv/h, was recorded at the points of missile impact in the Kaztal region.

The article reviews the issues of forming fish populations and studying the current state of commercial fish species in the delta lakes of the Syrdarya River for subsequent effective development of fish farming. In 2020, research works were carried out on lakes Akbilek, Tushchy, Shomishkol, Karakol and Akshatau-Sorgak of Aral District of Kyzylorda Region. At each of them, local ichthyofauna were identified and studied by way of experimental catches. Subsequently, the ichthyologic material was selected, processed and underwent biological analyses. The research also included the determination of physical and geographical parameters of target lakes, as well as evaluation of their chemical water composition. Experimental and control fish catches were carried out using fixed nets with 18-60 mm cells. For biological analysis, 239 fish were selected, including: snakehead (1 sample), wild carp (3 samples), crucian carp (9 samples), roach (102 samples), pike perch (25 samples), pike (26 samples), bass (35 samples), rudd (19 samples), sabre carp (1 sample), bream (11 samples), and asp (11 samples). The suitability of target lakes for further fish husbandry use was determined based on research findings and available literature and archival data.

The study aimed to assess the efficiency of the pilot hydro-acoustic (sonar) fish protection device (SFPD) installed at the Kokaral Dam of the Small Aral Sea. For this purpose, between August 27 and September 5, 2020 experimental and control fish catching was carried out using fixed fishing nets (30×60 mm mesh). The SFPD’s effectiveness was assessed based on the amount and species diversity of the caught fish with and without the SFPD operating. Fish behavior and distribution were monitored using an echo sounder. In terms of quantity, 173 fish were caught with the SFPD off, and 94 with the SFPD on. In terms of biomass, the values were 37.5 kg and 27.6 kg, respectively. With the SFPD off, the ichthyofauna composition was represented by 12 fish species: carp, crucian carp, roach, ide, bream, common rudd, saber carp, snakehead, pike perch, perch, pike, and asp. With the SFPD on, roach and ide were absent in the catch, and the quantity of common rudd significantly decreased. In both catches, the quantity of carp and crucian carp was similar; bream and saber carp specimen were sporadic. The number of predatory fish (pike, perch, snakeheads, and pike perch) in the catches increased. Asp was absent in the net catches also; however, this fish species represents the main object of amateur hook and line fishing. Based on the catch-per-effort unit, it can be concluded that whereas the SFPD observed efficiency for small non-predatory fish like ide, roach, and common rudd was 95%, it was 0% for large non-predatory fish (carp and crucian carp); and negative for predatory fish.

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.