Comparative Hematological Profiles of Migratory and Non-migratory Fish Species from the Lower Danube River

Abstract

Hematological parameters are widely recognized as reliable indicators of fish health and physiological adaptation to environmental conditions. The present study aimed to characterize the hematological profile of six economically important fish species from the lower Danube River, representing different ecological strategies: Alosa immaculata, Alosa tanaica, Aspius aspius, Silurus glanis, Cyprinus carpio, and Abramis brama. Blood samples were obtained through caudal vein puncture, and erythrocyte count (RBC), hemoglobin concentration (Hb), hematocrit (Ht), and erythrocyte indices (MCV, MCH, and MCHC) were determined using standard fish hematology methods.

Significant interspecific differences were observed in the erythrocyte-related parameters. The migratory species A. immaculata and A. tanaica exhibited the highest erythrocyte counts, hemoglobin concentrations, and hematocrit values, indicating an enhanced oxygen transport capacity associated with the elevated metabolic demands of anadromous migration. In contrast, erythrocyte indices showed comparatively limited interspecific variation, suggesting that the increased oxygen-carrying capacity of migratory species is achieved primarily through an increase in erythrocyte number rather than substantial changes in erythrocyte morphology. The presence of immature erythrocytes in peripheral blood smears of A. tanaica further suggests enhanced erythropoietic activity during migration.

The results provide baseline hematological reference values for economically important fish species from the lower Danube River and contribute to a better understanding of species-specific physiological adaptations. These data may support fish health assessment, ecological monitoring, aquaculture practices, and sustainable fisheries management.