The Monogenea (Class: Platyhelminthes,) are common parasites of the skin and gills of both marine and freshwater fish. This study aimed to the assessment of the prevalence percent, seasonal prevalence,  intensity of parasitism, clinical and post mortem lesions with an estimation of organic materials in the farm water of infested cultured Black Seabream (Spondyliosoma cantharus)with capaclidae sp. in a private fish farm in the Gulf of Suez, Egypt. The study was performed on 240 Black Seabream of body weight ranged 250-1000 gm. Survey on cultured marine fish was performed periodically each season for one year. Clinical and post mortem, parasitological, total and seasonal prevalence examination,  determination of ammonia, nitrite, and nitrate in cultured water and determination of physicochemical parameters of water during different seasons. Infested Spondyliosoma cantharus fish appeared with dark colour, suffered from respiratory distress; increase of opercular movements, with opening mouth, abnormal swimming, and flashing. Hemorrhages at the abdominal region, the caudal fins were observed. Scales sloughing with shallow wounds at different regions of the body and congestion of gills were noticed. The isolated parasite is subclass: Monogenea, order: Monopisthocotylea, Family: Capsalidae, Genus: Caballerocotyla. The concentration of organic matter was closely related to the prevalence of  Caballerocotyla sp. From the present study, it was concluded that Caballerocotyla sp. (Monogenea; Capsalidae) parasite isolated from the Red Sea cultured  Spondyliosoma cantharus fish in a private fish farm in the Gulf of Suez, Egypt. The prevalence of ofCaballerocotyla sp. was closely related to the concentrations of organic matter (ammonia, Nitrite, and Nitrate).