Peculiarities of ligulosis of bream (Abramis brama Linnaeus, 1758) and roach (Rutilus rutilus Linnaeus, 1758) in the Dnipro (Zaporizhzhiа) reservoir

Purpose. Study of the peculiarities of ligula infestation of roach and bream in the Dnipro (Zaporizhzhia) reservoir and the influence of Ligula intestinalis on the morphological and cytometric parameters of infected fish species. Methodology. The work presents the generalized results of studies conducted in 2020-2021 during planned test catches. Sampling was carried out along the shoreline of the Dnieper (Zaporizhzhia) reservoir in the lower part of the villages of Viiskove and Mykilske-na-Dnipri, Dnipropetrovsk region, in the summer-autumn period. The morphological study was carried out by carefully examining the surface of the scales and skin cover. Special attention was paid on fins, the amount of mucus, its consistency, color change, the presence of tumors, hemorrhages, ulcers, cysts, large ectoparasites, and the condition of eyes. The parasitological study was carried out by a complete anatomical dissection of the fish according to the classical method. Blood was collected at the catch site from the heart of the fish using a needle and a syringe into a dry test tube for the biochemical serum analysis. Blood was also collected for the preparation of smears and their subsequent microscopy. Blood smears were fixed with methyl alcohol and stained according to Romanovsky’s method with Giemsa’s standard solution. Blood smears were examined by microscopy at a 40x magnification. Blood smears of non-infected fish were used for comparison. Thirty fields of view were examined in each smear. Findings. In the course of the study, a decrease in the weight and condition factor of infected roach and bream was observed, and irreversible pathological changes in the internal organs caused by the mechanical pressure and migration of parasites were recorded. In addition, deviations from the normal values were found in the formed elements of blood. About 24.3% of erythrocytes in infected specimens of bream and roach were deformed: the cell membrane was not clear, erythrocytes had a slightly inflated shape. In some erythrocytes, the nucleus was faintly visible. Infected specimens had more juvenile forms of erythrocytes compared to non-infected fish. Originality. For the first time, a comparative morphological, cytometric analysis of blood during ligulosis infestation of infected specimens of bream and roach in the Dnipro (Zaporizhzhia) reservoir is presented. Practical value. The study of biological, clinical and epizootic peculiarities of parasitic helminths is of urgent interest for both science and fish farming. The obtained results can be implemented in the practical activity of fish farming and used in the development of measures to limit and prevent the development of parasitic diseases among the ichthyofauna of the Dnipro (Zaporizhzhia) reservoir.