Assessment of the toxic effect of hexavalent chromium on the hematological indices in Nile tilapia, Oreochromis niloticus

The presence of heavy metals, which are typically released into water bodies as a result of fast industrialization, causes the aquatic environment to become extremely contaminated. Chromium is one of the most common heavy metal in the environment and is used in several types of industries. The effect of sublethal toxicity of hexavalent chromium Cr(VI) on hematological indices of the Nile tilapia, Oreochromis niloticus has been analyzed following exposure of concentration 9.349 mg/L and 18.698 mg/L (10% & 20% of LC50 value ) of potassium dichromate (K2Cr2O7) as hexavalent chromium for 7, 15, 30 days. Hematological parameters are the most important indicators of fish health status. The aim of this study was to determine the effect of Cr(VI) toxicity on hematological parameters in O. niloticus. The results show that hemoglobin percentage (Hb%), red blood cell (RBC), mean corpuscular volume (MCV), and platelet count level were significantly (P > 0.05) decreased and the total count of white blood cell (WBC) was significantly (P > 0.05) increased with increasing time of exposure at a concentration of 9.349 mg/L of K2Cr2O7 in the test groups compared to the control group. At the concentration of 18.69 mg/L, Hb%, RBC, MCV, mean corpuscular hemoglobin concentration (MCHC), and platelet count level were significantly (P > 0.05) decreased and the total count of WBC and erythrocyte sedimentation rate (ESR) value were significantly (P > 0.05) increased with the increasing time of exposure in the test groups compared to the control group. To study the R2 value of the linear regression equation, we found that the trend of the chronic toxic effect of hexavalent chromium at 60 and 90 days of both the sublethal concentrations 9.349 mg/L and 18.69 mg/L of K2Cr2O7, where the value of Hb, RBC, packed volume cell (PCV), MCV are found to drastically decreased and the value ESR and WBC are found to drastically increased in the experimental groups compared to the control group. The investigation recommended that the presence of hexavalent chromium in the aquatic medium has a strong impact on the hematological indices in O. niloticus.