This study was performed to detect the presence of some microbes which cause diseases in ornamental fish, pathogenesis of Aeromonas hydrophila togoldfish (Carrassius auratus), in addition todetect the more sensitive antibiotics for these microbes also, with trials for treatment of the most prevailing bacteria. One hundred apparently infected ornamental fish namely fantail, goldfish (Carassius auratus auratus) Black molly (Poecillia latipinna) and koi carp (cyprinus carpio) was randomly collected from private ornamental fish shops. The clinical examinations of these naturally infected fish were recorded. Standard microbiological methods were used for isolation and characterization of bacteria associated with diseased fish. The results revealed that the prevalence of bacterial diseases was 38 % among the examined fish. The isolated and identified bacteria were Aeromonas hydrophila in a percentage of 23.75%, Pseudomonas aeruginosa in a percentage of 22.5%   and Enterobacteriaceae in a percentage of 53.75%. Pathogencity of selected bacterial isolate belonged to A. hydrophila was done through experimental challenge via immersion route. Clinical signs and postmortem lesions were recorded; nearly the same clinopathological picture which noticed in naturally infected fish. The therapeutic efficacy of   Enrofloxacin (2mg/L with 24 hours between dosing) was evaluated in the treatment of artificial infection with A. hydrophila in goldfish. Mortalities of fish were reduced by   administered daily as compared to control group. The isolation frequencies of A. hydrophila in each group during and after medication indicated that Enrofloxacin (Mortril) seemed to give good protection against A. hydrophila in goldfish. Antibiotic sensitivity tests revealed that A. hydrophila were sensitive to sulphatrimethoprim, ciprofloxacin, gentamicine, florfenicol, enrofloxacin and norfloxacin. Pseudomonase sp. were sensitive to oxytetracycline, gentamicine and ciprofloxacin, while Enterobacteriaceae were sensitive to gentamicine and ciprofloxacin.