Abstract
The freshwater fish Tilapia nilotica served as an aquatic model widely distributed in Egypt's High Dam lake to assess the ultrastructural alterations in skeletal muscles induced by exposure to diazinon or neopybuthrin. The fish were exposed to 1.5 times the LC sub(50) value of each pesticide. When the fish were exposed to this concentration of diazinon, severe splitting and fragmentation of myofibrils was evident. Phagocytic lysosomes of different sizes were abundant. Marked degeneration of muscles was observed in fish exposed to neopybuthrin. The contractile elements in many fibers were placed by granular homogeneously dense material.