The objective of the present study was to test the protective upshot of calcium carbonate against the gifted toxicity of arsenic to the Nile cat-fish (Clarias gariepinus). Enhanced hepatosomatic index (HSI) and reduced gonadosomatic
index (GSI) and intestinal index (ISI) as well as some of the tested blood parameters were recorded for fishes exposed to arsenic spotlight (1/10 & 1/20 LC50). The plasma levels of aspartate aminotransferase (AST), alanine
aminotransferase (ALT), total bilirubin, direct bilirubin, total lipids, glucose and total protein were significantly increased in fishes exposed to arsenic toxicity. Likewise, the activities of AST, ALT and lactate dehydrogenase (LDH) in the
liver and muscles were radically increased, whereas the total protein and glycogen contents in these organs were significantly abridged following arsenic exposure; this may be an indication of energy expenditure attributable to arsenic
toxicity. The histological examinations of the liver and gills renewed arsenicinduced
degenerative changes of these organs. Furthermore, the addition of calcium carbonate as a limiting agent induces reversibility of most of these arsenic – induced changes, especially those of fishes subjected to 1/20 LC50 of
arsenic. Consequently, calcium carbonate could be feasible to be used for the fortification of C. gariepinus in opposition to arsenic toxicity.