Parasitic crustaceans as a potential vector of MDR Vibrio alginolyticus infection among farmed marine fish in some earthen-pond based Egyptian aquaculture facilities: Molecular, epidemiological and pathological evidences.

Parasitic crustaceans affecting cultured marine fish in earthen-pond aquaculture facilities are nasty parasites that trigger cascades of microbial infections with consequent economic losses. In the current study, the role of some parasitic crustaceans in spread and transmission of bacterial infections among cultured marine fishes was investigated utilizing taxonomical, molecular, epidemiological, and pathological assays. A total of 400 marine fish involving Pomadasys stridens, Dicentrarchus labra, Sparus aurata, and Tilapia zilli have been randomly collected from some private earthen pond-based aquaculture facilities. Collected fishes were clinically examined for possible presence of disease symptoms, lesions and/or parasites. Three parasitic crustaceans were identified from gills, skin, and fins of examined marine fish species. The isopod Livoneca redmanii, Caligus, and Lernanthropus species were fully identified. Vibrio alginolyticus was concurrently isolated from both fish and isopod species with 99.76 % similarity between fish and isopod species upon molecular screening utilizing 16SrRNA with sequence alignment. Interestingly, 73.3 % of the isolated bacteria exhibited multi-drug resistance (MDR) with multiple antibiotic resistance (MAR index), values ≥0.2. Further, 56.7 % (17/30) of recovered isolates were resistant to four and five antimicrobials with MAR indices of 0.50 and 0.40. Histopathological examination has revealed remarkable damage of gill filaments and fins of affected fish.