Morganella morganii is an opportunistic pathogen widely spread out within the intestinal tracts of mammals, humans and reptiles as a part of normal intestinal microbiota. The appearance of skin lesions in blood parrot cichlid, Amphilophus citrinellus x Paraneetroplus synspilus, were monitored in separate aquariums withO2 8 mg/L, pH 7.8, water hardness 145 mg/L CaCO3, and water temperature at 28 °C for two weeks. Initially, superficial lesions were appeared on the fish skin and gradually penetrated the muscles after one week and finally resulted in fish death. Samples from various organs including edges of skin lesions, muscle and kidney, spleen, and liver were taken under aseptic conditions, inoculated into tryptic soy agar incubated at 25°C and 37°C for 24 h. The isolated bacteria from the kidney, spleen or liver were characterized using microbiological and molecular methods. Phenotypic and molecular assays resulted in the identification of Morganella morganii as the cause of skin lesions. Ninety apparently healthy goldfish (Carassius auratus) were challenged with isolated bacteria at 5.4 × 104 CFU /mL as a bath for one hour under stress and non-stress conditions. Affected goldfish developed superficial lesions, fin necrosis, muscle necrosis, and mortality initiated six days after challenge and reached 60 % (18 fish) and 36.66 % (11 fish) in stressed and non-stressed goldfish, respectively after 14 days. This data confirmed M. morganii as the causative agent of freshwater fish aquariums, and thus need to be considered in the disease diagnosis in aquaculture activity.
