Co-infection of infectious spleen and kidney necrosis virus, Aeromonas hydrophila, and Aeromonas dhakensis in native endemic Canara pearlspot Etroplus canarensis of Western Ghats, India

Abstract

The ornamental fish trade plays a critical role in global aquaculture, with endemic species like the Canara pearlspot (Etroplus canarensis) contributing to the industry’s economic and ecological significance. This study reports the first documented case of co-infection of infectious spleen and kidney necrosis virus (ISKNV) with Aeromonas hydrophila and Aeromonas dhakensis in Canara pearlspot from the Western Ghats, India. Clinical signs observed in the infected fish included skin darkening, hemorrhages, fin rot, splenomegaly, and nephromegaly. Histopathological analysis revealed necrosis and vacuolar degeneration in the liver, spleen, and brain tissues. Molecular diagnostics confirmed ISKNV and bacterial infections, with ISKNV showing 100% genetic similarity to isolates from ornamental fish in Australia, Ghana, Japan, and India. Phylogenetic analyses further classified A. hydrophila and A. dhakensis as highly virulent and moderately virulent, respectively, with antibiotic resistance profiles revealing multi-drug resistance (MDR) in both bacterial isolates. In vivo challenge studies demonstrated significant mortality due to ISKNV, while the lethal dose (LD₅₀) for A. hydrophila and A. dhakensis was calculated to be 7.1 × 10⁵ CFU/mL and 2.37 × 10⁷ CFU/mL, respectively. These findings highlight the vulnerability of native endemic species to emerging pathogens, emphasizing the urgent need for enhanced biosecurity measures and targeted interventions to mitigate the risks associated with co-infections in aquaculture and ornamental fish systems.