The concentrations of the heavy metals (Cr, Zn, Cu, Pb, Cd, Hg, and Fe) in water of Lake Bardawil and Lake Manzalah were estimated. The concentrations of Cr and Zn were not significantly different in the two lakes. However, the concentrations of the other heavy metals were significantly higher in Lake Manzalah than in Lake Bardawil. Histological and ultrastructural alterations were observed in Mugil cephalus of Lake Manzalah, but these microscopic manifestations of such fish of Lake Bardawil appeared normal. The muscle fibres of Mugil cephalus of Lake Manzalah showed fragmentations, deep myolysis and splitting. In some regions the myofibrils appeared as spiral-shaped ropes.
Key words: Histology, ultrastructure, skeletal muscles, mugil cephalus, Lake Bardawil, Lake Manzalah.