, vol. 69, no. 4 , pp. 263-285, 2009.
The present study was carried out to evaluate the protective effect of vitamin C (vit. C) against genotoxic and pathological changes induced by arsenic (As), zinc (Zn) and their mixture in Oreochromis niloticus. Fish of almost the same weight and size were divided into 13 groups (6 groups were exposed for 3 weeks and the other 6 groups were exposed to the same treatment but for 6 weeks) beside the control group (10 fish/group). The 1st group was served as control, the 2nd group was exposed to 2.9 mg/L of As in the form of sodium salt in water for 3 weeks. The 3rd group was exposed to As plus vit. C (10mg/kg diet equivalent to 30 gm/kg bw). The 4th group was exposed to 3mg/L of Zn in the form of zinc sulfate. The 5th group was exposed to Zn and vit. C. The 6th group was exposed to both As and Zn. The 7th group was exposed to As, Zn and vit. C. Five samples from each group were sacrificed at 3rd and 6th week of the experiment, respectively, and subjected to cytogenetical and histopathological examination. Gross lesions were recorded along the time of exposure. The results revealed genotoxicity in O.niloticus exposed to As and/ or Zn for 6 weeks. There was a significant increase of micronuclei (Mn) in all As and/or Zn exposed fish groups, compared to the control, while the treatment with vit. C significantly decreased the frequency of Mn in all As and/or Zn exposed groups. The histopathological examination revealed severe pathological lesions in gills, skin, muscles and liver in case of As toxicity, while in case of Zn toxicity, the changes were common in liver and spleen and other internal organs. In both cases, vit. C protects the tissue against such toxicity. In conclusion, this study proved that As and Zn had genotoxic effect on O.niloticus and that appear in the significant increase in the frequency of Mn induced by these metals, whereas the treatment with vit. C reduced that genotoxic effect especially with long term treatment. In addition, the histopathological lesions were recorded in As and/or Zn exposed groups for 3 w, whereas the alterations were more clear in 6 w exposed groups. Minor or no lesions were noticed in all vit. C treated groups.
