Due to the economic importance of the marine and fresh water fishes, it was necessary to investigate the important parasitic monogeneans that infest one of the marine fishes; Scomberomorus commerson inhabiting the Mediterranean Sea in Damietta region in Egypt and the Nile fish Oreochromis nilotica, as monogenea have been responsible for important epizootic events with serious consequences. The study revealed the presence of the polyopisthocotylean monogenean species Gotocotyla aegypticus, Pricea multae and Pseudothoracocotyla gigantica on the gills of the marine fish. The Nile fish was infested by the monopisthocotylean monogenean fluke Enterogyrus cichlidarum in the stomach. Comparative anatomy is the area of interest in this study by means of different techniques which are the traditional histological methods by light microscopy in addition to scanning electron microscopy and detailed ultrastructural studies using transmission electron microscopy. The study highlighted the attachment organs and the construction of its parts and there was a focus on exploring surface specializations associated with the tegument, apertures and some reproductive organs.