Chemical agents can able to induce changes in the various haematological components [1]. Estimation of haematology and biochemical parameters (determination of glucose concentration in blood) is used as an index of fish health status in a number of fish species to detect physiological changes following variety of stressors [2, 3, 4]. Furthermore, non-destructive haematological technique and changes in the proportion of blood parameters may be indicative and sensitive biomarker of the biological effects of metals in fish [5].
The aim of this study was to analyse the changes in haematological and biochemical parameters in Rainbow trout's (Oncorhynchus mykiss) peripheral blood after exposure with metals (Zn – 0.1, Cu – 0.01, Ni – 0.034, Cr – 0.01, Pb – 0.014 and Cd – 0.0015 mg/L (2013/39/EB; 2008/105/EB)) mixture at various time points (4, 7 and 14 days). Haematological biomarkers were assessed as differentiation of leukocytes and the relative abundance of thrombocytes and different types of leukocytes in fish blood and the measurement of blood haematocrit levels. Biochemical indices – assessed concentration of glucose in O. mykiss blood.
O. mykiss peripheral blood samples were taken from fish caudal vein with synergies (rinsed with 3.8% sodium citrate solution). The differential count of leukocytes and thrombocytes was performed by microscopy at a magnification of ×1,000 (Olympus BX51, Japan) in Giemsa-stained peripheral blood samples. Differentiation of leukocytes and the relative abundance of analysed cell types was determined by counting a total of 300 leukocytes on each slide [4]. Haematocrit levels were determined directly by microhematocrit centrifugation. Concentrations of glucose in fish blood were determined by using the automatic Glucose Analyser (EKSAN-Gm, ANALITA, Joint-Stock Company Ltd, LITHUANIA). The minimum detection limit of the blood glucose method is from 2 to 30 mmol/L and the error for repeated measurements (precision) is ≤5%. Minimal blood sample volume per measurement is 50 μL.
Statistically significant induction of thrombocytes was estimated in all exposure groups of treated O. mykiss. The number of thrombocytes in fish from 7-days group was 5 times higher, while after 14 days treatment there was found only 4 times higher induction in comparison to control. In all exposure groups there was observed two times higher elevation of neutrophils number. Moreover, induction in neutrophils (neutrophilia) and monocytes after 7 days exposure differed significantly in comparison to control. The levels of haematocrit and concentrations of glucose did not vary significantly between exposure groups and in comparison, to control.
Based on the presented results it can be concluded that chemical stress (exposure with six metals mixture) induces both thrombocytosis and neutrophilia in fish. The measuring of haematological parameters in fish is useful biomarker and was performed in wide range of fish species after exposure to different trace metals [5, 6, 7]. The understanding of toxicant uptake, behaviour and responses in fish may, therefore, have a high ecological relevance and pollution risk prediction.