In the present study we investigated the alteration in the activity of two metabolic enzymes [Glucose-6-Phosphate Dehydrogenase (G6PDH) and Lactate Dehydrogenase (LDH)] and the histological changes on liver and gills of the African catfish Clarias gariepinus collected from 6 sites along the river Nile, from its spring at Aswan to its estuary at Rosetta and Damietta branches. The results showed that the physical and chemical parameters of the water collected from Damietta and Rosetta branches were higher than those of the water collected from other sites. Remarkable alterations in the activity of the selected enzymes in the liver and muscles of the African catfish were detected. These alterations go in parallel with the elevation in the levels of chemical parameters detected in the water of Damietta and Rosetta branches as a result of pollution stress in these areas. The activity of G6PDH was significantly (p < 0.05) decreased from Aswan to Rosetta and Damietta recording the highest value at Rosetta followed by Damietta water. The activity of LDH showed a significant elevation (p < 0.05) in activity in the liver and muscles of fishes collected from Rosetta and Damietta branches comparing to other sites. These alterations in enzymatic activities were followed, in the present study, by the occurrence of histological lesions and clear damage in liver and gill tissues of the African catfish collected from the same sites. Thus we may conclude that, the altered activities of G6PDH and LDH could be useful biomarkers of water pollution. At the same time, histopathology provides a reliable, easily quantifiable index of low-level toxic stress to a broad range of environmental pollutants.
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