Biochemical contents in the muscle of Oreochromis niloticus were determined in fish specimens collected from El-Kanater, Benha, Zefta and Talkha stations. Analysis revealed that the water content in muscles was higher in immature than mature fish. The maximum values of protein content in fish flesh were recorded during spring at Benha and Zefta stations. Seasonal variations in the amount of protein, fat. carbohydrate water and ash were observed. The fat in fish muscles was fairly high in winter and early spring in adult specimens, i.e.. during the pre-spawning months, then it dropped after the breeding season. A direct relationship between fat and protein was found. The muscle carbohydrate was correlated to feeding and spawning activity. High energy values were found throughout the prespawning period.
Heavy metals concentrations were detected in the muscles of O.niloticus and found to follow the order: Fe > Pb > Cu > Zn.
The histopathological study of fish muscles showed marked signs of haemorrhage and hemolysis.