Stress inevitably occurs during any fish handling and manipulation in culturing, research, or clinical examination situations that require capture and removal of fish from water. Different stress factors can affect the changes in the relative numbers and function of cells of the fish immune system. Catching, transportation and over-crowding caused stress-induced changes in the total number of leukocytes and thrombocytes, as well as changes in the leukocyte formula in Prussian carp (Carassius gibelio, Bloch, 1782) presented here. Cytochemical characterization of leukocyte cell types was performed by applying Myeloperoxidase (MPO), Periodic Acid Schiff (PAS) and Sudan Black B (SBB) staining of Prussian carp blood smears. Cytochemical characterization is a rapid and efficient method for white leukocyte differentiation and insight in their functional status. Comparison and analysis in Prussian carp hematological parameters from fish with and without exposure to stressful conditions such as capture, manipulation, transport and holding, revealed significant differences between stressed and non-stressed fish. Significant reduction in the total number of thrombocytes and lymphocytes and the increase in total neutrophil count were observed in stressed animals. However, differences in total leukocyte number and the number of monocytes were not observed. Deviations from the estimated reference intervals for Prussian carp hematological parameters clearly indicated the presence/absence of a stress reaction and to some extent its intensity. Estimated reference intervals and characterization of morphological and cytochemical appearance of blood cells form a solid basis for further research of the cellular immune function and hematology changes in Prussian carp.
