This study aimed to assess the toxic effect of the overconcentration of salt (NaCl) in farmed common carp fish, Cyprinus carpio L. in floating cages in Al-Saqlawiyah Rgion in Iraq. The salt was used at 13.8% which led to fish mortality reached to 70% through 96 hours of exposure. The fishes exhibited lethargy during 10 minutes with abnormal nervous signs and imbalance swimming with progressive decreases in opercular movement frequency. The gills appeared as cooked gill lesion with excessive

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... s secretion and congestion in the hepatic, gastrointestinal and kidney tissues. Microscopical examination of gills showed hyper trophy in both pillar cells and mucus cells, variable in severity code of both epithelial hyperplasia and occlusion of lamellar space as well as epithelial cells lifting had been determined and vacuolar degeneration in hepatic cells with severe multifocal infiltration of inflammatory cells and necrosis in liver. Histopathological analysis of kidneys revealed interstitial nephritis while in the intestine, the microscopic examination exhibited hydropic degeneration of mucoid cells, hyperplasia of enterocytes and desquamation of the epithelial cells of villi. The conclusion of this study was that histopathological analysis can be used as biological indicators for evaluation of effects of NaCl overconcentration in fish organs.