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The present study investigated Vibriosis in cultured Gilthead Seabream at the Suez Canal area, Egypt. Two hundred moribund fish samples subjected to clinical, microbiological and histopathological examinations. Retrieved isolates were biochemically identified using API 20 E system then confirmed by conventional PCR. Antibiogram profiling of the retrieved isolates was also done. Naturally infected fish showed severe ascites, hemorrhages and erosions in the skin and fins. A sum of 29 V. alginolyticus isolates were retrieved from the examined samples. Targeting 16SrRNA and groEl genes produce an expected product with a length of 336, 301bp size bands; respectively, were found from all tested strains of V. alginolyticus. The antibiogram profiling of V. alginolyticus isolates showed resistance to Ampicillin, Gentamycin followed by Ciprofloxacin with high sensitivity to Sulphamethoxazole/Trimethoprim and oxytetracycline. Histopathological alterations in the affected tissues showed, inflammatory reactions together with degenerative and /or necrotic changes in branchial, liver and kidney. Ultimately, the current study emphasizes the critical fish health threats posed by V. alginolyticus with subsequent influences on human. Thus, competent biosecurity strategies should be adopted to control Vibrio infection in marine fishes and to minimize the antimicrobial resistance hazards in mariculture.

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This research was carried out to study the bacterial etiology of ulcerative syndrome in Nile tilapia (Oreochromis niloticus) and its associated environmental stressors. A total of 90 live and moribund Nile tilapia showing signs of ulcerative dermatitis were collected from various fish ponds in El-Sharkia Province, Egypt, during the summer seasons from June 2019 to August 2020. Collected fish were subjected to full clinical and postmortem investigation followed by bacteriological and molecular identification of the bacterial agents as well as histopathological examinations. Moreover, water samples from the fish sampling sites were collected and analyzed physiochemically and microbiologically. Furthermore, the pathogenicity of the isolated strains was assessed by challenging apparently healthy Nile tilapia to determine the LD50. Clinically, the examined fish exhibited ulcerative dermatitis as focal or fused large ulcers surrounded by red zones of hemorrhages at different body parts. Bacteriologically, Aeromonas veronii biovar sobria and A. caviae were isolated and identified. Moreover, 16S rRNA gene sequencing and phylogenetic analysis verified the identity of these species. Antibiogram profiling of the recovered Aeromonas sp. isolates showed complete resistance to ampicillin, with high susceptibility to gentamycin, trimethoprim/sulphamethoxazole, and erythromycin. Histopathological examination of the affected fish revealed epidermal necrosis with dermal edema and an influx of inflammatory cells into the dermis and hypodermis. The LD50 of A. veronii biovar sobria and A. caviae was estimated as 1.5 × 107 and 1.5 × 108 CFU/fish; respectively. The water temperature and ammonia concentrations recorded a significant rise (P ≤ 0.05) in July and August compared to June; however, the highest pH levels were recorded during August, followed by July. Also, the total bacterial load significantly increased (P ≤ 0.05). Finally, it was concluded that the improvement of water quality helps sustain the health of farmed fish .