Edwardsiella ictaluri infection in farmed striped catfish Pangasianodon hypophthalmus in India : E. ictaluri in Indian aquaculture.

Edwardsiella ictaluri is a devastating intracellular bacterial pathogen, responsible for significant losses in the aquaculture sector. It affects over 40 fish species including striped catfish Pangasianodon hypophthalmus. In the present study, a case of large-scale mortalities (~ 70–80%) in farmed P. hypophthalmus from Uttar Pradesh, India was investigated. The affected fish exhibited erratic swimming, haemorrhagic vent, pinpoint ulcerations on skin, and white foci in the internal organs. Wet mount examination of gills and skin scrapings showed no parasites. Histopathological examination of the naturally diseased fish showed necrotic granulomas in kidneys, and multifocal necrotic areas in spleen and liver. Notably, bacterial isolates recovered from the diseased fish were presumptively identified as E. ictaluri based on phenotypic tests. The isolates were confirmed as E. ictaluri based on amplification of species-specific fimbrial gene, and amplification and sequencing of 16S rRNA and gyrB genes. The phylogenetic analysis revealed that sequences of gyrB gene of E. ictaluri provided higher species-level resolution compared to 16S rRNA sequences. Furthermore, following experimental infection with E. ictaluri, 100% mortality was observed in striped catfish. The clinical signs and histopathological lesions resembled those of naturally infected fish, and E. ictaluri was re-isolated from the experimentally infected fish. Based on these observations, it was confirmed that E. ictaluri was responsible for mortalities in the farmed striped catfish. Considering the rapid expansion of striped catfish culture in the country, and documented susceptibility of cyprinids and cichlids in other countries, the emergence of this pathogen is a significant concern in Indian aquaculture.