الفهرس 
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Abstract
The rapid and ongoing development of Egyptian mariculture sector continues to call for better health management to face new challenges. Actual risks have to be assessed frequently through extensive field surveys concurrently with repeated and controlled experimental trials. Study of disease outbreaks targeted seabream, Sparus aurata L., and seabass, Dicentrarchus labrax L., cultured in two models of mariculture, floating net-cages and earthen ponds in the Northern Egypt was conducted. Each farm noticed unique serious
seasonal episodes of high mortalities. Disease problems recorded during this period were investigated,
focusing on phenotypic, molecular identification, antimicrobial sensitivity, pathogenicity and
clinicopathological alterations noticed in the infected fish. A total number of 200 moribund and ∕ or freshly
dead marine fish samples showing picture of clinical septicemia were inspected through the course of these
episodes. V. alginolyticus was the most prevalent bacterial pathogen 30.63 % followed by Ps. fluorescens
21.62 %. S. agalactiae and T. maritimum were accused for 18.91 % % and 15.31% % respectively. Infections
attributed to V. vulnificus recorded the lowest rate 13.51%. Isolates varied in their antibiotic sensitivity pattern.
Resistances were eminent in strains recovered from Alexandria farm. Circulatory, degenerative, proliferative
and necrotic changes were evident in histopathological sections. Disease conditions were found to be
associated with the existence of stressful environmental role expressed by unfavorable values of water quality
measures especially temperature, Dissolved oxygen, ammonia, nitrite and existence of some heavy metals in
affected fish farms.