Effects of zinc exposure on the accumulation, haematology and immunology of Mozambique tilapia, Oreochromis mossambicus

Abstract

Changes in the haematological and innate immune parameters and accumulation in the liver, gill and muscle tissues were investigated in Mozambique tilapia (Oreochromis mossambicus, L.1758), which were semi-statically exposed to several zinc concentrations in vivo. The fish were exposed to low (1 mg L^-1), medium (2.5 mg L-1) and high (5 mg L^-1) concentrations of zinc for 14 days. In this study, significant changes were seen in the haematological and innate immune parameters of the fish exposed to zinc in comparison to those of the control group (p<0.05) at day 14. In all groups exposed to zinc, a decrease in the erythrocyte count (RBC) and lymphocyte percentage and an increase in hemoglobin (Hb), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH) values and neutrophile percentage occurred (P<0.05). A decrease in white blood cell (WBC) count and an increase in mean corpuscular hemoglobin concentration (MCHC) values occurred with medium and high concentrations (P<0.05). As per hematocrit (Hct) values, a decrease with high concentrations and an increase with low and medium concentrations were found (P<0.05). In all groups exposed to zinc, a decrease in phagocytic activity was found, and an increase in lysozyme and myeloperoxidase activities were observed with medium and low concentrations (P<0.05). A decrease was found in nitroblue tetrazolium (NBT) activity with medium and high concentrations; in the lysozyme and myeloperoxidase activities was found with high concentrations (P<0.05). In this study, the highest zinc accumulation rate was found in the liver tissue, and the lowest rate was found in the muscle tissue. Accumulation of zinc metal in the tissues was found to increase directly proportional with the ambient concentration and exposure duration (P<0.05). In conclusion, it was found that exposure of O. mossambicus to Zn concentrations affected haematological and innate parameters adversely. Therefore, these parameters can be used to predict the effect of metals such as zinc on fish populations.

Keywords: Zinc, haematology, immunology, accumulation, Oreochromis mossambicus

African Journal of Biotechnology Vol. 12(7), pp. 744-753