Establishing bacterial infectivity models in striped Catfish Pangasianodon hypophthalmus (Sauvage) with Edwardsiella ictaluri.

A bacterial infectivity challenge model of Edwardsiella ictaluri in striped catfish was developed. All experiments were conducted using a bacterial isolate of E. ictaluri that had been recovered during a natural outbreak of bacillary necrosis of Pangasianodon (BNP) in farmed striped catfish Pangasianodon hypophthalmus in Vietnam. Time of immersion in 107  CFU.ml-1 had a significant effect on mortality. The immersion bacterial dose of 107  CFU/ml for 30 s resulted in a cumulative percentage mortality of 63%. Three to four days post-bacterial challenge, fish showed gross clinical signs of natural BNP and E. ictaluri was recovered and identified from these fish. Moreover, a cohabitation challenge was evaluated as an alternative challenge method, although the mortalities among the infected fish were lower at around 15%-40%. This study confirmed the horizontal transmission of E. ictaluri in striped catfish and elucidated that cohabitation challenge could be used in reproducing the disease under controlled conditions.