Chemical pollution poses adverse effects on aquatic organisms, including altered gene expression. This study, therefore, investigated the hepatic expression of biomarkers of exposure and effect in Oreochromis niloticus inhabiting the drainage canal of a sugarbeet factory (an industrially polluted habitat) and the Nile River (a reference habitat). Compared to the Nile River, the drainage canal contained significantly elevated levels of heavy metals (Cd, Fe, Mn, Co, and Pb), nitrate, ammonia, nitrite, chemical oxygen demand, and biological oxygen demand. The liver of O. niloticus from the drainage canal accumulated significantly higher concentrations of the heavy metals. O. niloticus from the drainage canal had significantly higher hepatic expressions of genes related to oxidative stress (GSTa, GPx, and NRF2), metal toxicity (MT), endocrine disruption (Vtg), and hypoxia (HIF1a) and a significantly lower hepatic expression of the apoptosis-associated CAS gene. CYP1A (a detoxification biomarker) expression did not exhibit significant differences. These results provide insights into complex adaptive responses of O. niloticus to multiple chemicals and support the utilization of molecular biomarkers as warning signals for water pollution.
The invasion of fish by heavy metals is a recognized environmental problem. Heavy metals, after leaking into the water, penetrate fish directly through the gill and later the skin. Fish develops protective defence mechanisms against the damaging effects of heavy metals. This study was aimed to investigate the concentrations of certain metals (cadmium, iron, manganese, cobalt, and lead) in the muscle tissues of the Nile tilapia (Oreochromis nilo ticus) and their possible impact on its histological, nanomechanical, and biochemical biomarkers. The results showed that fish muscle from the polluted site contained high levels of heavy metals compared to the reference site. Biochemical profile of the Nile tilapia showed that serum glucose, total proteins, uric acid, creatinine, bilirubin, superoxide dismutase, and malondialdehyde were elevated in exposed tilapia compared to their corresponding reference. Histological examination of the liver showed severe alterations in the liver tissue. Nanomechanical properties (roughness and stiffness) confirmed the damaging effect of metals on the liver tissue. These findings provide a rational application of histological, nanomechanical and biochemical parameters to be used as indicators of metal stress. Integrated biomarker response is a comprehensive index of all biomarkers and a good indicator of the health status of aquatic ecosystem.
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