Aeromonas allosaccharophila, an emerging opportunist pathogen for farmed hybrid sturgeon (Acipenser baerii x Acipenser schrencki), in southwest China

Aeromonas allosaccharophila belongs one of the causative agent of Aeromonas disease in teleosts. Here, we reported on multiple outbreaks of A. allosaccharophila with mortality up to 80% in farmed hybrid sturgeon in Sichuan, China, from 2019 to 2021. This was the first study to A. allosaccharophila from diseased hybrid sturgeons by phenotypic characterization and 16S rRNA analysis. The typical clinical signs of these fish were intestinal segments empty and often with yellow mucus or swelling. Histopathological observation of diseased fish infected with A. allosaccharophila showed the intestinal villus structure disappeared and the intestinal mucosa epithelium was necrotic and shed. Experimental infection indicated that A. allosaccharophila was the pathogen responsible for the mortalities. Antibiotic sensitivity test results showed that A. allosaccharophila was resistant to ampicillin, neomycin, tetracycline, and penicillin, while sensitive to sulfamethoxazole, streptomycin, florfenicol, enrofloxacin, and cefoxitin. Our findings provide references for the disease diagnosis and treatment.