الفهرس 
AcknowledgmentOnly 14 pages are availabe for public view
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Abstract
The aim of the present work :To gain a better understanding of hexavalent chromium toxicity in Nile tilapia Oreochromis niloticus using a panel of biomarkers which are typical targets of metal toxicity Expand the role of biomarkers in environmental assessment, so they can give information concerning the potential consequences of exposure and can serve as more effective tools in ecological monitoring system The present work studies the effect of exposure of fresh water Nile tilapia, Oreochromis niloticus to two sublethal concentrations of hexavalent chromium (15 and 30 mg/l) for 6 weeks to investigate the impact of pollution on plasma, brain, liver, gill, and muscles of O. niloticus using a panel of biomarkers. Measured parameters Plasma analysis: Haemoglobin, glucose, protein content, acetylcholinesterase, Urea, Uric acid. Muscle analysis: Muscle total protein, lipids, Muscle water content.Brain analysis: Brain acetylcholinesterase Gill analysis: Gill ATPase. Liver analysis: Antioxidant Enzymes: Superoxide dismutase (SOD), Glutathione S- transferase (GST), Glutathione reductase (GR), Glutathione peroxidase (GSHPx). Non- Enzyme Antioxidants: Metallothionein MT. Hemoglobin content decreased throughout the experiment period, compared to the control. Moreover, the plasma glucose content and uric acid increased in both Cr6+ concentrations. Plasma urea decreased during the first 24 h of exposure, then it increased, thereafter decreased and finally fish recovered. Also, the brain AChE of the lower concentration showed significant fluctuations starting with inhibition of the enzyme then activation and final tendency to recover, while the higher concentration showed a significant increase throughout the whole experimental period with no sign of recovery. Plasma AChE has been inhibited and no sign of recovery was detected. Gill Na+-K+-ATPase specific activity remained unchanged in fish exposed to both Cr6+ concentrations during the whole experimental time. Liver metallothionein (MT) content increased in both fish treated with Cr6+ concentrations.