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Diseases of Aquatic Organisms

    DAO prepress abstract   -  DOI: https://doi.org/10.3354/dao03425

    Strain variability and pathogenic potential of tdh gene-carrying Vibrio parahaemolyticus isolated from diseased Penaeus monodon

    P. Shaheer, P. G. Akhilnath, V. N. Sreejith, Toms C. Joseph*, V. Murugadas, K. V. Lalitha

    *Corresponding author:

    ABSTRACT: A disease outbreak in 42 d old black tiger shrimp Penaeus monodon juveniles from a commercial aquaculture farm in Kerala, India was investigated. The cause of the disease outbreak was confirmed as Vibrio parahaemolyticus by biochemical tests, PCR targeting the toxR gene and by pathogenicity testing of the isolates. All the isolates tested negative by PCR specific for V. parahaemolyticus associated with acute hepatopancreatic necrosis disease (AHPND) implicating vibriosis unrelated to AHPND as the cause of mortality. Among the 19 isolates obtained, 2 isolates possessed the tdh gene (coding for thermo-stable hemolysin) whereas none of the isolates possessed the trh gene. The LD50 value of eight isolates of V. parahaemolyticus from diseased and apparently healthy shrimps ranged from 2.7 x 104 to 4.9 x 105 CFU ml–1 by immersion challenge of P. monodon postlarvae. BOX-PCR and dendrogram analysis of the bacterial isolates revealed that the isolates from moribund and apparently healthy shrimps formed separate clusters indicating the origin of these isolates are from separate clones. The isolates from moribund shrimps including tdh-positive V. parahaemolyticus clustered together. The present study represents the first report of tdh-positive V. parahaemolyticus causing disease in shrimp farm.