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An important food-producing sector in Egypt is aquaculture and fisheries; however, several pathogenic microorganisms lead to high mortalities and significant economic losses. The occurrence of Psychrobacter glacincola infection among 180 wild marine fishes collected from the Red sea at Hurghada, Egypt were investigated in the present study. The disease prevalence rate was 6.7%. The recovered isolates were subjected to biochemical and molecular identification. The study also investigated pathogenicity and the antibiogram profile of the recovered isolates. The clinical examination of the infected fish revealed various signs that included lethargy and sluggish movement, hemorrhages and ulcers on the body and the operculum, scale loss, and fin congestion and rot, especially at the tail fin. Furthermore, during postmortem examination, congestion of the liver, spleen, and kidney was observed. Interestingly, 12 isolates were recovered and were homogenous bacteriologically and biochemically. The phylogenetic analysis based on 16S rRNA gene confirmed that MRB62 identified strain was closely related the genus Psychrobacter and identified as P. glacincola and was pathogenic to Rhabdosargus haffara fish, causing 23.3% mortality combined with reporting a series of clinical signs similar to that found in naturally infected fishes. The present study also showed that P. glacincola isolates were sensitive to all antibiotics used for sensitivity testing. Our findings add to the body of knowledge regarding the occurrence of pathogenic P. glacincola infection in Egyptian marine fishes and its potential effects on fish. Future large-scale surveys exploring this bacterium among other freshwater and marine fishes in Egypt would be helpful for the implementation of effective strategies for the prevention and control of this infection are warranted.

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Bacteria are one of the most prevalent causes of morbidity and mortality among wild fishes. Vibrio alginolyticus (V. alginolyticus) is a serious fish pathogen. This study was performed to investigate prevalence of V. alginolyticus infection among six species of Red Sea fishes at Hurghada city, Egypt through clinical and bacteriological examinations and to determine pathogenicity of the isolates and their antimicrobial susceptibilities. Therefore, a total number of 180 fish from these six fish species (30 fish of each species) were randomly collected from the Red Sea at Hurghada city during the period from October 2019 to March 2020 and subject to clinical and bacteriological examinations. Based on the morphological and biochemical characteristics of the isolates, 64 homogenous V. alginolyticus isolates were isolated and phenotypically identified from the examined fishes with prevalence of (26.7%), (20%), (63.3%), (36.7%), (23.3%) and (43.3%) among Lutjanus ehrenbergii (L. ehrenbergii), Lethrinus borbonicus (L. borbonicus), Siganus rivulatus (S. rivulatus), Rhabdosargus haffara (R. haffara), Scarus ghobban (S. ghobban) and Cheilinus lunulatus (C. lunulatus) fishes respectively. Afterthat, representative isolates were cofirmed as V. alginolyticus by 16S rRNA gene sequence and deposited in GenBank as V. alginolyticus MR-C17 (GenBank accession no. MW790239). The V. alginolyticus infected fishes exhibited skin dark coloration, scales loss, hemorrhages on several parts of the body surface, mouth, base of fins, abdomen, opercula and around the anal opening, eroded fins, ascites, swollen intestine and congestion or paleness of the internal organs espeially liver. Antimicrobial susceptibility testing of V. alginolyticus isolates revealed that they were sensitive to chloramphenicol, tetracycline, ciprofloxacin and ofloxacin and resistant to ampicillin, cephalothin, amikacin, streptomycin, cefotaxime, erythromycin, oxolonic acid, amoxicillin/clavulanic acid, tobramycin and clindamycin. Pathogenicity test revealed that V. alginolyticus MR-C17 was pathogenic to R. haffara with 80 % mortalities in the experimentally infected fish which showed similar clinical signs and post-mortem (PM) lesions to thoes observed in the naturally infected fishes.