Fish blood is a highly informative medium for assessing homeostasis, turning hematological parameters such as hematocrit, hemoglobin concentration, cell counts, and morphological abnormalities into promising biomarkers for evaluating fish health, diagnosing diseases of various etiologies, and biomonitoring aquatic ecosystems. However, their practical application is limited by a lack of reference data for many species inhabiting natural environments. The aim of this study was to perform a cytomorphological analysis of the peripheral blood of bream (Abramis brama (L., 1758)) from Lake Syamozero (Republic of Karelia) and to characterize the erythrogram and leukogram. The study subjects were mature individuals of both sexes, aged 3+ to 9+ years, caught in June 2024. Hydrochemical analysis of the water confirmed that the maximum permissible concentrations of pollutants were not exceeded, allowing this reservoir to be considered a model system for establishing reference parameters. Using light microscopy of stained blood smears, we performed differential leukocyte counts and assessed morphological abnormalities in erythrocytes. A majority of the blood cells examined were mature erythrocytes, with juvenile forms not exceeding 2.4 %. Among erythrocyte abnormalities, poikilocytosis was the most common (10 % of erythroid cells on average). Other findings included erythrocytes with an eccentrically or peripherally located nucleus (in 5.0 % of fish), agglutinated cells (in 25.0 % of individuals) forming chains of 3 to 27 cells, erythrocytes with a scalloped edge (no more than 1.0 % of all erythrocytes, observed in 75.0 % of fish), and occasional signs of amitotic division (singular findings). The leukogram of the breams exhibited a typical lymphoid profile (lymphocytes accounting for up to 89 % of leukocytes), with pseudoeosinophils predominating among granulocytes. No statistically significant differences in blood cell counts were found between sexes. The data obtained fill gaps in Leuciscidae hematology, provide quantitative criteria for assessing the physiological state of individuals and populations, and can serve as a basis for comparative analysis in toxicological, ecological, and aquaculture research. It is also necessary to expand the image database of bream hemocytes to enable automated differential hemocyte counting using neural network modeling methods.