Studies were undertaken to determine toxicological effects in a model species, Cyprinus carpio L. following hypoxic exposure either alone or in combination with representative heavy metal (i.e. copper; Cu) via a dietary route, at different levels of biological organisation (viz. biochemical, histological and individual level effects). Initially, the validation study of biological responses using a range of concentrations of dietary Cu as a relevant environmental contaminant was carried out (Chapter 3). The results showed a range of biological responses in exposed fish including significant genotoxic response as determined by induction of DNA strand breaks (i.e. the Comet assay) with bacterial enzymes Fpg and Endo-III (for detection of oxidative DNA damage) and reduction in growth rate suggesting the robustness of selected biomarkers. Subsequently, this approach was used initially to determine the biological responses following chronic hypoxic and hyperoxic exposure (Chapter 4). The results suggested that both hypoxic and hyperoxic conditions lead to a range of comparable biological responses. Following relative evaluation of chronic hypoxic and hyperoxic exposures, experiments were carried out to elucidate potential interactive effect of hypoxia in combination with dietary Cu (Chapter 5). The combined exposure of hypoxia and Cu induced a significantly higher level of DNA damage suggesting that DNA damage in fish can serve as a sensitive biomarker for changes in water quality as well as presence of genotoxic chemicals. The final sets of experiment were carried out to determine the biological responses in C. carpio following exposure to chronic hypoxic stress and subsequent recovery in normoxic condition for 7 days. Real-time PCR (qPCR) technology was used to examine the hypoxia inducible Factor-1 α (HIF-1α) gene expression pattern (Chapter 6). The results suggested that the expression levels of HIF-1α in response to hypoxia were significantly higher compared to normoxic controls, a high level of oxidative DNA damage under hypoxia and re-exposure to normoxic condition (i.e. recovery period). This will shed lights for development of adaptive response in higher vertebrates, which could also have significant clinical implications in human health.

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