Pathological and microbiological assessment of hemorrhagic septicemia in cultured juvenile Russian sturgeons (Acipenser gueldenstaedtii)

Aquaculture has experienced sustained growth, now surpassing capture fisheries in global production. Among cultured species, sturgeon aquaculture has likewise expanded recently, prompting increased research and surveillance of diseases affecting this taxon. In this context, fifteen farmed Russian sturgeons ( Acipenser gueldenstaedtii ) were submitted for pathological investigation. A comprehensive study was conducted, encompassing autopsy, histopathology, parasitology, microbiology, and antimicrobial resistance analysis. Macroscopic examination revealed ulcerative lesions on the scutes, multiorgan hemorrhages, and multifocal black lesions in the liver. Histological analysis revealed a systemic granulocytic inflammatory response with associated melanomacrophage infiltration affecting the skin, gills, liver, spleen, heart, and digestive tract. Multifocal necrosis and hemorrhages were also present, consistent with hemorrhagic septicemia in fish. Microbiological identification confirmed the presence of Aeromonas spp., Citrobacter spp., and Plesiomonas shigelloides , all known pathogens associated with this condition in sturgeons. All three genera included isolates exhibiting resistance to at least one of the three antibiotics tested, with C. braakii displaying multidrug resistance. Additionally, Flavobacterium succinicans was also detected, representing the first report of this bacterium in sturgeons associated with skin ulcers. In conclusion, this study provides a detailed characterisation of hemorrhagic septicemia in Russian sturgeons, with pathological examination proving essential for identifying systemic lesions and validating microbiological findings. The detection of antimicrobial resistance raises concerns about the efficacy of current therapeutic options in potential future outbreaks, emphasising the importance of rapid and integrated diagnostic approaches, continued surveillance, and the implementation of effective preventive health management strategies in aquaculture. • A complete macroscopic and histological description of hemorrhagic septicemia in Russian sturgeons has been provided. • A complex infection pattern involving multiple bacterial agents was identified using MALDI-TOF technology. • The antibiotic resistance profile has been updated in Russian sturgeons affected by hemorrhagic septicemia. • Flavobacterium succinicans has been detected for the first time in ulcerative lesions in sturgeons.