الفهرس 
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Abstract
Amyloodinium ocellatum is one of the most important ectoparasitic protozoa infecting marine species especially during early life stages (fries and fingerlings). Whether the environmental parameters and water quality affecting the occurrence of Amyloodinium infestation is worth to be investigated as a tool for proper control strategies. The present study was carried out on 1065 cultured European seabass of diffrerent life stages (768 fry-219 fingerling and 78 adults) that were collected during the period from April 2017 to April 2018. The collected samples subjected to full clinical, parasitological and histopathological examination studies. The results revealed a heavy infestation with Amyloodinium ocellatum causing severe hyperplasia in the affected gill epithelia with fusion of the secondary gill lamella and moderate hyperplasia in the skin with desquamation of the covering epithelium. The prevalence and seasonal dynamics of infestation by Amyloodinium ocellatum revealed that the highest infestation rate was during spring season with followed by autumn season then summer season then the lowest infestation rate during winter season.Interaction between the environmental stressors and Amyloodinium ocellatum infestation showed that pH and salinity were positively correlated with Amyloodiniosis. As well as examining the antiseptic activity of hydrogen peroxide against the ectoparasitic protozoan A. ocellatum as a trial for treatment. It was cleared that, the treatment with hydrogen peroxide with a concentration 20% in two doses 100ppm & 200ppm for two weeks was more effective, safe and excellent and that was confirmed through lower the load of parasitic infestation and recovery of infested fishes with no mortalities were recorded at the end of the treatment trial.