Molecular Characterization and Pathogenicity of Vibrio atlanticus and Vibrio rotiferianus Associated With Mortality of Cownose Ray Rhinoptera bonasus

Abstract

The vulnerability of cownose rays (Rhinoptera bonasus) to anthropogenic pressures, such as overfishing and habitat degradation, necessitates urgent and comprehensive conservation efforts to ensure the species’ survival and maintain the marine ecosystem balance. In this study, six cownose rays, acquired post-mortem from a public aquarium, were meticulously examined under controlled laboratory conditions. Through the PCR targeting of the housekeeping genes and subsequent sequencing, gene fragments were concatenated into a 2022-bp sequence deposited in the PubMLST database. PCR and sequence analyses identified two distinct Vibrio isolates, labeled as gv9 and gv10, which by MLSA analysis were shown to be closely related to Vibrio atlanticus and Vibrio rotiferianus. A novel sequence type, ST 247, was identified, suggesting allelic differences compared to 60 closely related Vibrio species. Despite the absence of external lesions, internal examination revealed muscular, uterine, cardiac and endometrial hemorrhage, valvular intestinal dilatation, uterine pus accumulation, and pyometra. Histopathological examination demonstrated hemorrhage in the heart muscle, an increased number of microglial cells in the brain and severe vacuolar degeneration in the liver. This study provides insight into the intricate association between cownose rays and Vibrio bacteria, as well as the potential role of these bacteria in the pathologies observed.