Studies based on biochemical and hematological parameters in fish are significant in monitoring of health and early detection of pathological conditions. This research obtained values of serum electrolytes and hematological parameters in crucian carp (n = 15) and common carp (n = 13). Significantly different values of K, Cl and Ca concentration were detected. In serum of common carp there were significantly higher concentration of K and Cl and lower concentration of Ca, compared to the crucian carp. Hematological parameters differ in these two species. In blood of common carp significantly lower PCV, hemoglobin concentration, RBC and MCV and notably higher MCHC and WBC were obtained, compared to crucian carp. This preliminary research is important in establishing referential range of biochemical and hematological parameters in cyprinid fishes.

Although tench prefer environments with plenty of aquatic vegetation and they can tolerate quite low oxygen level, also they are sensitive to drastic temperature increase. In this research, biochemical parameters in the serum of tench (Tinca tinca Linnaeus, 1758) during thermal stress were analysed in controlled environmental conditions. Both the control and experimental group consisted of 25 specimens. The experimental group of fish was exposed to water at 28 oC for 30 minutes. Puncture of the heart was done and the blood serum was analyzed. Statistical data analysis showed that thermal stress led to increased concentration of mineral electrolytes (sodium, potassium, calcium and chloride ions) and increased concentration of glucose. The significant increase was only detected regarding the concentration of calcium (p<0.000) in blood serum. Keywords: blood serum – electrolyte concentration - glucose concentration – tench - thermal stress

The effect of fluoride on the calcium level in serum was analyzed in the laboratory rat Rattus norvegicus. The control group consisted of 10, and the experimental group of 15 animals. In the experimental group, fluoride at a concentration of 3 mg/100 g body weight of rats was intramuscularly injected into the musculus gluteus maximus. The concentration of calcium was measured by the CPC method. The average serum calcium concentration was 2.46 mmol/l, with female rats having higher values of serum calcium than male rats. Fluoride caused the reduction of calcium concentration in serum (p<0.05); the reduction was significantly expressed in female rats (p<0.000).