The environment has a permanent influence on a series of physiological and biochemical
processes in the organism, causing certain changes in these processes and functions. Hematological
parameters, such as number of erythrocytes, their size, hemoglobine concentration, number of leukocytes
and differential blood count, can provide key data in understanding the state of the organism. The number
of erythrocytes in the blood of the fishes is constant and the body of the fish maintains this number
within certain physiological limits, thanks to the activities of physiological homeostatic mechanisms that
provide the balance between the process of erythrocyte formation and their degradation. In this study, the
determination of morphometric characteristics of erythrocytes in the species Gobio obtusirostris was
performed with the aim of obtaining the basic physiological characteristics of the species, as well as
determining the degree of sensitivity of the species to changes in the environment. In the research were
used the Gobio obtusirostris individuals that were caught on the Vrbanja River, in the area before the
confluence of the Vrbas River. Blood samples of these fishes were used to make blood smears. A total of
11 individuals of Gobio obtusirostris were analyzed, and the analysis included 100 mature red blood cells
on each preparation. Besides analyzing mature erythrocytes, the analysis also included young forms.
Based on the comparison of all obtained values of the morphometric parameters of erythrocytes of the
species Gobio obtusirostris with the results of studies by other authors, it can be concluded that the
obtained values are lower in relation to the mentioned characteristics in most other species of the
Cyprinidae family. By comparing the values of the morphometric characteristics of the immature and
mature forms of erythrocytes in Gobio obtusirostris, significant differences were found.
