CHANGES IN THE HISTOLOGICAL STRUCTURE OF TISSUES AND ORGANS OF PIKEPERCH (SANDER LUCIOPERCA LINNAEUS, 1758) AND PERCH (PERCA FLUVIATILIS LINNAEUS, 1758) FROM THE ZAPORIZHZHIA RESERVOIR UNDER THE INFLUENCE OF HUMAN IMPACT.

Purpose. The aim of the study was to investigate morphological and histological features of the gills, liver and blood of percids – pikeperch (Sander lucioperca Linnaeus, 1758) and perch (Perca fluviatilis Linnaeus, 1758) from different areas of the Zaporizhzhia Reservoir. Methodology. The study was conducted in two areas of the Zaporizhzhia Reservoir – in the Samara Bay and the lower part of the reservoir near the Viyskove village. The material was collected during research fish surveys in the summer-autumn period of 2024. The object of the study were age-3+ pikeperch and perch. The number of fishes used in the study was 20 specimens of each species. Hematological and histological studies were carried out according to generally accepted methods. The concentration of heavy metals in water samples was determined on a C115-M1 atomic absorption spectrophotometer in mg/L. Findings. According to the content of Cd, Mn, Cu, and Zn in both studied areas of the Zaporizhzhia Reservoir, there was an excess of the MPC for water bodies used for fishery purposes. The difference between the cytometric parameters of fish from different areas of the Zaporizhzhia Reservoir was mostly insignificant (р≥0.05), except for the width of the pikeperch nucleus and the area of the perch erythrocyte nucleus, which were significantly larger in the fish of the Samara Bay (р≤0.05). The results of the study indicate the dependence of changes in the formed elements of the blood on the physiological state of the fish and on their environment. Among the studied fish of the lower part of the reservoir, the largest count of erythrocytes with pathological changes was observed in pikeperch, it was 1.32 times higher than in perch. Among fish of the Samara Bay, the highest count of pathologies in blood cells was also noted for pikeperch and was 1.17 times higher compared to that of perch. The results of these studies indicate an unfavorable ecological condition in both areas of the Zaporizhzhia Reservoir. The histological studies of the fish liver showed a number of pathological phenomena were revealed. The most common pathology of the liver cells of the studied fish from both areas of the reservoir was necrosis in pikeperch from the Samara Bay. Fish in the lower part of the reservoir had significantly fewer pathologies. Histological analysis of pikeperch and perch gills showed a high degree of pathological changes. The majority of pathologies were detected in pikeperch from the Samara Bay, which may indicate an average degree of pollution of the water by heavy metals and oil products. Based on these data, the histo-morphometric parameters of percid tissues can be used in the future to assess the ecological state of the water and the level of human impact of the Zaporizhzhia Reservoir, as well as be used as an additional indicator during the comprehensive assessment of the impact of anthropogenic factors on hydroecosystems. Originality. For the first time, a study of the morphological and histological characteristics of the gills, liver, and blood of percids (pikeperch and perch) from different areas of the Zaporizhzhia Reservoir was conducted. Practical Value. Histo-morphometric parameters of percid tissues can be used in the future to assess the ecological state of water and the level of human impact of the Zaporizhzhia Reservoir, as well as be used as an additional indicator during the comprehensive assessment of the impact of anthropogenic factors on hydroecosystems. [ABSTRACT FROM AUTHOR]