Heavy Metals in Organs and Tissues of Silver X Bigheads Carp Hybrid as Indices of Anthropogenic Pressure in Areas with a High Level of Urbanization А.А. Makarenko 1,a* , P.G. Shevchenko 1,b , I.S. Kononenko 1,c , V.M. Kondratyk 1,d , D.S. Khrystenko 1,e , V.V. Grubinko 2,f 1 National University of Life and Environmental Sciences of Ukraine, Kyiv, Ukraine 2 Ternopil National Pedagogical University named after V. Hnatyuk, Ternopil, Ukraine a almakarenko912@gmail.com, b shevchenko.petr@gmail.com, c kononenko_irina88@ukr.net, vadkondratyk@ukr.net, e dskhrist@gmail.com, f v.grubinko@gmail.com Keywords: pond, hybrid silver x bighead carp, gills, liver, muscles. Abstract. The growth of man-caused load on natural objects, including surface waters, gave impetus to the studying for issue of water pollution in Ukraine by various pollutants. Especially relevant for us are the studies of fishery reservoirs as a direct environment for growing quality aquaculture products. Among the toxic compounds contained in reservoirs, one of the first places is occupied by heavy metals. On the one hand, heavy metals, as pollutants in natural waters, pose a great danger because even in relatively small concentrations they can adversely affect aquatic organisms. On the other hand, in microquantities most heavy metals (except mercury, cadmium and lead) are a natural and even essential component of living cells of aquatic organisms, including fish [17,19]. Zn, Mn, Fe, Cu, Pb, Co, Ni, Cd in the organs and tissues of the bighead carp hybrid form, which was cultivated in ponds from highly urbanized territory, are distributed heterogeneously and their level of content depends not only on the physical and chemical characteristics of the aquatic environment or this heavy metals biochemical activities force in fish organisms, but also on functional features of concrete organs and tissues of the latter. Results of our investigations showed that above mentioned heavy metals were characterised by high levels of content in the organs and tissues of hybrid silver x bighead carp. Highest content in organism of hybrid are lead, cobalt, and cadmium. Highest concentration of heavy metals in our investigations was recorded in gills, because it is the first defence line of fish organism from environmental pollutants. Introduction Fish ecology and development of fish productivity in water bodies appear to be the urgent tasks of modern scientific research. The productivity of different fish species in freshwater ecosystems depends on environmental conditions. Fish, like any other aquatic organisms, respond sharply to the quality of aquatic environment. In addition, they are an important link in the unremitting movement of micro- and macronutrients – metals that are essential elements for normal development of aquatic organisms in different water bodies. Such elements as Zn, Mn, Fe, Cu, Pb, Co, Ni, Cd play a significant role in implementation of numerous physiological and biochemical processes (due to the influence on activity of enzymes and enzymatic complexes). Heavy metals accumulate in fish organs and tissues depending on geochemical environmental conditions, nature of water bodies, functional state of fish organism, and type of food chain [5,16,20]. One of the urgent tasks of modern ichthyological and ecological research is the analysis of the accumulation peculiarities of heavy metals in the organs and tissues of freshwater fish, which was grown in aquaculture, from areas with a high level of urbanization [7]. The content level and distribution specifics of heavy metals in fish organisms directly determine both the fish productivity of the water body and the safety of aquaculture products for the final consumer. Due to the high biological activity, heavy metals, depending on the concentration and time of exposure, as well as many other factors, can be characterized by both positive and negative effects on hydrobionts in International Letters of Natural Sciences Submitted: 2020-10-23 ISSN: 2300-9675, Vol. 83, pp 55-68 Revised: 2021-05-20 doi:10.18052/www.scipress.com/ILNS.83.55 Accepted: 2021-07-08 CC BY 4.0. Published by SciPress Ltd, Switzerland, 2021 Online: 2021-07-27 This paper is an open access paper published under the terms and conditions of the Creative Commons Attribution license (CC BY) (https://creativecommons.org/licenses/by/4.0)