Fatal Hemorrhagic Septicemia in Common Guitarfish (Rhinobatos rhinobatos) Caused by Photobacterium damselae Subsp. damselae in a Controlled Environment

Elasmobranchs, including sharks and rays, are commonly housed in public aquariums due to their ecological significance and educational value. The common guitarfish (Rhinobatos rhinobatos), currently listed as 'Critically Endangered' by the IUCN, is particularly susceptible to population declines due to overfishing and bycatch. While generally considered robust, individuals in captivity may experience stress-related health issues, increasing their susceptibility to infectious diseases. This study investigates a mortality event affecting three 20-year-old guitarfish kept in a public aquarium. The fish exhibited respiratory distress and ataxia before sudden death. Necropsy findings included external hemorrhages and severe hemorrhagic enteritis. Bacteriological analyses identified Photobacterium damselae subsp. damselae in all specimens through MALDI-TOF and PCR sequencing, while parasitological tests and RT-PCR for Betanodavirus were negative. Histopathology revealed bacterial aggregates in the gills, heart and kidney, consistent with systemic bacterial septicemia. P. damselae subsp. damselae is an opportunistic marine pathogen known to cause hemorrhagic septicemia in various fish species. This case represents the first documented occurrence of fatal P. damselae subsp. damselae septicemia in captive guitarfish. Understanding the impact of infectious diseases in confined environments is essential for improving the health management of endangered elasmobranchs in aquariums and conservation programs.