The influence of increased zinc concentrations (0.1, 0.5, 1.0, 1.5 and 2.0 mg(-1) ZnSO4 x 7H2O) on the total number and the morphology of the erythrocytes, as well as the processes related to their formation and destruction in the spleen of Carassius gibelio were investigated ex situ. It was found that zinc concentrations caused pathological alterations in the erythrocytes that were not identical in the different concentrations-poikilocytosis; ruptures in cell membranes in the concentrations of 0.5mg(-1) and 1.5 mg(-1); cells with double nuclei (symplasts); in the concentration of 1.0 mg(-1); in the highest concentrations (1.5 mg(-1) and 2.0 mg(-1)) presence of erythrocytes at initial stage of atypical mitotic division. Against the background of those various alterations, the total number of the erythrocytes in the peripheral blood increased simultaneously with the increase of zinc concentrations (p < 0.001). Morphological alterations in the spleen were also observed, indicating a compensational tendency against the toxic influence of zinc upon the fish erythrocytes-hyperplasia of the red pulp and lack of hemosiderin. These results show that the alterations in the total number and the morphology of the erythrocytes are connected with the relevant compensatory histopathological alterations in the spleen. The use of the ascertained alteration could be valuable in monitoring zinc-polluted waters.