The influence of the nematode Eustrongylides excisus (Jägerskiöld, 1990) on the body of monkеy goby (Neogobius fluviatilis Pallas, 1814) caught in the lower part of the Dnipro (Zaporizhzhia) Reservoir

Purpose. To determine the specifics of the influence of the parasitic nematode Eustrongylides excisus on the physiological and biochemical parameters of monkey goby (Neogobius fluviatilis) in the conditions of the lower reach of the Dnipro reservoir. Methodology. The work presents results of studies conducted in the lower part of the Dnipro Reservoir the 2020-2023 - in the village of Voyskove and village Mykilske-on-Dnieper, Dnipropetrovsk region in the summer-autumn period. Parasitological study was carried out using 780 monkey gobies. Fish were immobilized by destroying the medulla with a dissecting needle. The parasitological study was carried out by a complete anatomical dissection of the fish according to the method of K. I. Skryabin. Morphological characteristics of parasites were determined according to the guides of Bauer (1987) and Gibson (2008). Blood sampling for the preparation of smears was carried out at the place of catch. Blood was collected from the caudal artery by cautodomy. Blood smears were examined by light microscopy using a SIGETA MB-115 SE microscope at a 40x magnification. Morphometric study of erythrocytes was carried out with the help of computer analysis of microphotographs, which were made using a digital camera “Sciencelab T500 5.17 M” connected to a SIGETA MB-115 SE microscope. A Mindray biochemical analyzer was used to determine the content of total protein, albumins, globulins and glucose in fish blood. Findings. The study did not show significant differences in the hematological parameters of infected and healthy specimens of monkey gobies, however, deformation and undulation of the plasmatic membrane of erythrocytes were detected. Histological specimens showed structural abnormalities in muscle tissue and intestines. Biochemical analysis of blood showed a slight decrease in the total content of globulins and glucose in infested fish. Originality. For the first time, a comparative morphological and cytometric analysis of blood as well as histological and biochemical analysis in the case of nematode infestation of monkey goby (Neogobius fluviatilis) under the conditions of the Dnipro reservoir has been presented. Practical value. The obtained results are important for the development of measures to limit and prevent the development of parasitic diseases among the ichthyofauna of the Dnipro Reservoir and can also be used in the practical activities of fish farms. Keywords: monkey goby, nematode, invasion, tissues, erythrocy