Vibrio parahaemolyticus a causative bacterium for tail rot disease in ornamental fish, Amphiprion sebae

•V. parahaemolyticus strain is highly pathogenic and the associated ECPs is an important causative agent of tail rot disease in A. sebae.•LD50 of V. parahaemolyticus and its extracellular protease were found to be 1 × 105 CFU and 5 μg/fish respectively.•V. parahaemolyticus and its ECPS has affected the immune organs of A. sebae.

The present study was performed to identify the tail rot disease causing bacterium in marine ornamental fish, Amphiprion sebae. Bacteria were isolated from the infected immune organs and tail region of A. sebae. Five different bacterial isolates (S1-S5) with different shape, size and colour were chosen for the infection study. The isolated strains were individually challenged with A. sebae at a constant dose of 1 × 107 CFU/fish. The virulent strain was found to be S-3, which showed maximum reproducing ability in A. sebae by causing typical tail rot disease and mortality. Furthermore, S-3 strain was identified as Vibrio parahaemolyticus by 16S rRNA gene sequencing (KF738005), biochemical analysis and amplification of tox R gene. Subsequently, extracellular products (ECPs) of V. parahaemolyticus were prepared by cellophane overlay method. The LD50 value of V. parahaemolyticus and its ECPS were found to be 1 × 105 CFU and 5 μg/fish. The histology results revealed that V. parahaemolyticus and its ECPS are the major cause of tail rot disease in A. sebae.