A total fifty diseased cat fish (Clarias gariepinus) were collected from private fish farms in Dakahlia governorate which suffered from cumulative mortality. All collected fish were subjected to clinical, postmortem, histopathological and mycological examination. Aflatoxins were extracted and quantitated from feed and musculature of infected fish using HPLC, blood samples were collected for biochemical and haematological parameters. The clinical observation revealed that the infected fish showed opacity of the eyes, yellowish greenish gills, hemorrhagic and yellowish skin, and the fish were slow in motion.The postmortem examination showed enlargement of the gall bladder,distention of the stomach,yellowish enlarged liver and the kidneys were swollen, dark red and friable whereas, the histopathological examination revealed a severe degenerative and necrotic changes in most internal organs. On the other hand Mycological examination of infected fish yeilded isolation of Aspergillus flavus (42%), A.parasiticus (34.8%) , A.niger (12%) and A.fumigatus (10.9%).The mean levels of aflatoxins in feed was 108.9 ppb(46.4 ppb AFB1,1.5ppb AFB2,58.9 ppb AFG1,2.1ppbAFG2),while the mean of AFs residues detected in musculature was 2o.8ppb(11.3,0.15,8.9,0.5ppb)respectively.Regarding to biochemical and hematological parameters, there was a significant decrease in serum Albumin and significant increase in AST,ALT and serum creatinine of infected fish which indicated liver and kidney damage.Also, there was significant decrease in Hb concentration and RBCs count whish indicated the high toxic effect of aflatoxins.