Gram-negative curved rods bacteria also known as the Vibrio are spread globally. Skilled colonizers of any kind of aquatic ecosystems from shallow to high depths. Some vibrios (e.g., V. anguillarum , V. ordalii , V. salmonicida , V. vulnificus , V. alginolyticus, etc.) can have pathogenic effects on aquatic life as in marine vertebrates and invertebrates. However, there are currently few reports in the literature on infectious diseases affecting sharks. Therefore, the aim of this study was to clarify the cause of tank mortality occurred in juveniles of lesser spotted dogfish Scyliorhinus canicula (Linnaeus, 1758), a small demersal shark (Carcharhiniformes: Scyliorhinidae) reared in an Italian public aquarium.
Sharks were placed in interconnected tanks (1 m3 each) with a recirculating aquaculture system (RAS) in accordance with the current legislation on animal welfare. A few months after hatching , elasmobranchs (Figure 1) showed the first symptoms, i.e., anomalies in swimming, fast breathing, and lack of appetite. Therefore, according to the Ethics Committee, 20 juvenile specimens (mean±SD : weighing 2.16±0.29 g, and total length 94.60±4.03 mm ) have been subjected to various analyses including necropsy, parasitological and virological examination, and b acteriological and b iochemical analysis . In order to exclude the presence of different pathogens of marine fish species (parasites, bacteria, Betanodavirus).
No external lesions were found, also the necropsy did not show macroscopic lesions of the viscera. Parasitological (internal and external examination) and virological (Betanodavirus RT-PCR) tests reported negative results. Regarding bacteriological analysis, positivity were retrieved in 12 out of 20 specimens (60%) from at least one matrix (i.e., head kidney, brain, or blood). However, the identification by VITEK-MS did not produce any valid results. All the 24 strains isolated shown a fragment of 730 bp from the rpoB gene amplification : 11 isolates (45.8%) were identified at species level as V. cyclitrophicus , whereas the remaining 13 (54.2%) as V. crassostreae (BLASTn nucleotide sequence identity value ranging from 98 to 100%).
Although the pathogenic role of these microorganisms has not been proved as well as the presence of other pathogens cannot be excluded, the study reported two Vibrio species in poorly studied aquatic animals. The weaknesses and strengths of the different diagnostic methods were also highlighted.