This study was carried out on 100 tilapias collected from Lake Temsah, Egypt. All data collected seasonally. Body weight, total length and sex were examined for all fishes. Both parasitological and histopathological examinations of external and internal organs were carried out. The maximum growth in T.zillii was at summer season with body weight 112 g and length 18 cm, but the lowest growth was at spring season with body weight 20 g and length 9.5cm. The highly parasitic infestations appeared at winter season (40%), the parasites ranges between protozoa cysts which appeared clearly inside the intestine which was unidentified species and encysted metacercariae found in several organs such as gills, liver and spleen. Autumn season come next (36%) with infestation only by encysted metacercariae. The summer and spring seasons were equally in parasitic infestations (16%) and both seasons infested by encysted metacercariae in gills, liver, and spleen but at spring season the protozoa cysts appeared clearly inside the intestine. The parasitic infestations lead to severe histopathological alterations of infested organs ranged between low and high which were helped in disease diagnosis. These alterations included hyperplasia, degeneration and fusion of gill filaments. Vacuolar degeneration of hepatocytes, atrophy and necrosis of surrounding hepatocytes. Severe hyperplasia of melanomacrophage centers (MMC).