LAUSR

Abstract A total of 108 water samples and 180 Sparus aurata were collected randomly and seasonally from private fishponds at Ismailia Governorate from September-2017 to August-2018. Fish were subjected to clinical and bacteriological examinations, while water samples were examined for physicochemical parameters, total Vibrio and bacterial counts. The potential influence of various environmental stressors on the disease occurrence was investigated using a model fish (Tilapia zillii), which were classified into 5 groups: G1, fish with skin abrasions; G2, fish exposed to high organic matter (O.M; 12 mg L−1); G3, fish exposed to low dissolved oxygen (DO; 2 mg L−1); G4, served as a positive control; G5, served as a negative control without infection or stress. The examined fish displayed corneal opacity, friable liver, and ascites. Vibrio anguillarum and V. parahemolyticus were the most prominent species with a prevalence of 68% and 32%, respectively. The PCR results showed that all retrieved isolates belonged to Vibrio sp. with amplicons size of 519 bp, while only V. anguillarm isolates were positive for the rpoN gene with fragments size of 120 bp. The principal component analysis was conducted to extract and determine the factors for water quality variations in four seasons of the year. The result showed that the total Vibrio count (TVC) and total bacterial count (TBC) were significantly correlated with water quality and seasonal variations. They exhibited significant (p ≤ 0.01) fluctuation between the examined water samples and positively correlated with water temperature and negatively with pH. The challenged fish showed signs of septicemia as observed in the naturally infected ones. V. anguillarum showed the highest count in stressed infected groups compared to control group. The mortalities were reported from highest to lowest in the following order in G1 (100%), G2 (80%), G3 (40%), and G4 (10%) indicating that loss of skin barrier increase the risk of Vibrio infection, followed by deterioration of water quality. Conclusively, environmental stressors have opposing effects on disease dynamics. Good management and sanitary measures are essential to prevent vibriosis.