Outbreak of Edwardsiella tarda in Cultured Pangasius hypophthalmus (Sauvage, 1878)

Abstract

Mass mortality and morbidity were reported from cultured Pangasius hypophthalmus (Sauvage, 1878) in an aquaculture farm in Kerala, India. Pure bacterial cultures were isolated and identified as Edwardsiella tarda from body ulcers and internal organs of moribund P. hypophthalmus and from sediments of farms without an outbreak. LD 50 in P. hypophthalmus models of the isolates from diseased fish and isolates from sediment samples were similar. PCR targeting esaV gene was unable to discriminate the pathogenic and non-pathogenic E. tarda. However, ERIC-PCR followed by dendrogram analysis differentiated isolates based on the presence of esaV gene. The isolates that did not carry the esaV gene also were found to be virulent in P. hypophthalmus fingerlings. Hence it can be assumed that the type III secretory system along with other virulence determinants contributes to virulence by E. tarda in fishes.