DIFFERENTIAL BLOOD COUNT OF TENCH Tinca tinca (Linnaeus, 1758) IN CONDITIONS OF THERMAL STRESS

Defining the physiological feature provides an understanding of functional adaptation of species to its ecological niche as well as the various forms of stress factors. This paper gives an overview of changes in certain forms of leukocytes (WBC differential) under the influence of thermal stress (increased temperature). In our experiment, we used 46 specimens of tench (Tinca tinca) fished in the Jablanica Lake reservoir. Specimens had previously been adapted in specially prepared tanks for 20 days.  The control group of animals (16) was exposed to constant water temperature of 10 0C, while in the treated groups (30), the water temperature was gradually risen to 28 0C and, as such, held for 30 minutes. All specimens were aged 2+ and 3+.It was found that the thermal regime change causes adaptive response of tench specimens by increasing the number of neutrophils and pseudoeosinophils but reduction in the number of lymphocytes. Observed were statistically significant differences in the number of segmented granulocytes, pseudoeosinophils and lymphocytes between the control and the experimental group. However, a significantly higher number of segmented granulocytes and pseudoeosinophils was at the experimental group, while in the control group a number of lymphocytes was significantly higher compared with the experimental group. Neither form of leukocytes showed any significant difference between males and females of the experimental group. It is interesting to note that among individuals from both the control and experimental group, eosinophils and monocytes were rarely noticed, while basophils were not found at all. Key words: thermal stress, tench, Tinca tinca, pseudoeosinophils