The present study was designed to investigate crustacean diseases affecting cultured marine fishes "seabass (Dicentrarchus labrax), seabream (Sparus aurata) and Meagre (Argyrosomus regius)". They were randomly collected from 4 private polyculture fish farms in the Suez Canal area and Damietta Governorates from December 2020 to November 2021. All examined fishes showed no pathognomonic clinical signs. Infested fishes had hemorrhages at different parts of the body. Some S. aurata were emaciated with abdominal distention and marbling of gills. Infested D. labrax showed marbling and sloughing of gill filaments with excessive mucous secretion while A. regius showed bulging of operculum in isopod-infested cases. The isolated crustaceans were identified as Livoneca redmanii and Nerocila orbignyi isopods from A. regius and S. aurata, respectively, and Lernanthropus kroyeri and Caligus minimus copepods from D. labrax. The total prevalence of crustacean infestation was 22.10%. The highest infestation was recorded in D. labrax (54.40%) followed by S. aurata (7.40%) and the lowest was recorded in A.regius (4.40%). Caligus minimus recorded the highest prevalence (9.30%) while Livoneca redmanii had the lowest prevalence (1.44%).