Abstract
This study was carried out to investigate the genotoxic and cytotoxic potentials of sublethal concentration (5mgL−1) of combined metals including Cd, Cu, Pb and Zn (1.25mgL−1 of each) on erythrocytes of Nile tilapia, Oreochromis niloticus after exposure for five and seven days; and to evaluate the protective role of vitamin E alone and a combination of selenium (Se) with vitamins A, C and E which was added to the diet as antioxidants against the genotoxicity and cytotoxicity of these metals. This was accomplished by application of micronuclei (MN), binuclei (BN), nuclear abnormalities (NAs) assays in addition to morphological erythrocyte alteration (MAEs) assay. The results revealed that, exposure of O. niloticus to Cd, Cu, Pb and Zn induced the formation of nine genotoxic endpoints including MN, BN and seven patterns of NAs, kidney-shaped nuclei, blebbed nuclei, lobed nuclei, bilobed nuclei, notched nuclei, hook-shaped nuclei and vacuolated nuclei; and five patterns of morphological malformations were recorded as cytotoxic endpoints including echinocytes, acanthocytes, teardrop-like erythrocytes, microcytes and fused erythrocytes. Frequencies of these abnormalities were significantly different (p<0.05) in comparison to control group. The maximum number of MN, BN and most of NAs and MAEs were recorded in the 5th day of exposure and then start to decrease as recorded in the 7th day. Addition of the vitamin E alone to the diet significantly (p<0.05) decreased the frequencies of MN, BN, and most of NAs and MAEs to become less than those recorded in metals-treated fish. But, addition of a combination of Se with vitamins A, C and E in the diet resulted in more significant decrease (p<0.05) in frequencies of MN, BN, NAs and most MAEs to become less than those recorded in both, fish treated with metals only and fish treated with metals and supplied with vitamin E alone in the diet. Therefore, this study confirms the powerful protective potential of the vitamin E alone and a combination of SE with vitamins A, C and E as antioxidants against the genotoxicity and cytotoxicity of Cd, Cu, Pb and Zn in erythrocytes of O. niloticus. Also, confirmed on the validity of MN test and NAs in addition to MAEs as effective indicators and valuable sensitive monitoring tools for detecting genotoxic and cytotoxic agents in the aquatic environment.
•Toxic effects of Cu, Cd, Pb and Zn in Nile tilapia, Oreochromis niloticus, were studied.•Heavy metals induced genotoxic impacts on erythrocytes of Oreochromis niloticus.•Se and vitamins A, C and E protect erythrocytes from genotoxicity of heavy metals.