Identification and pathogenicity of Plesiomonas shigelloides in Silver Carp

Plesiomonas shigelloides was isolated from diseased silver carp in Kolkata Wetland, West Bengal, India. It was associated with mortality of Silver Carp, Hypophthalmichthys molitrix, which is the most widely cultivable fish species in fresh water aquaculture. The P. shigelloides was identified based on the biochemical and molecular characterization and the pathogenicity was studied on H. molitrix. The 16S rRNA gene sequence of the present isolate (NCBI GenBank Accession Number- KX986915) revealed that, the isolate was 100% identical with P. shigelloides (NCBI GenBank Accession Number- MF100995). P. shigelloides killed 10-100% fish in experimental infection and the LD50 value was calculated as 1.3× 105CFU per fish with intraperitoneal injection. The challenged fish had subcutaneous haemorrhagic ulcers and reddening at injection sites, however there was no clinical sign observed in the gill. The histology of experimentally challenged H. molitrix showed the kidney alterations and exhibited shrinkage of epithelial cells in renal tubule and enlargement of glomerular cells.Liver showed focal accumulation of edematous fluid, necrosis and infiltration of heterophils indicative of bacterial infection. The pathology and pathogenesis studies of this pathogen in inland open waters like wetlands and lakes would help in management of the outbreak of disease in these aquatic ecosystems.