Photobacterium damselae (formerly Vibrio damsela) is an important pathogen, causing potential devastation to fish and shellfish aquaculture. Photobacterium damselae ssp. damselae has been reported to cause wound infections and fatal disease in human and a variety of marine animals. We have isolated this strain for the first time in the east coast of India from cage cultured cobia that was undergoing heavy mortality during 2016.
The objective of this experimental study was to investigate pathogenicity of Photobacterium damselae subsp. damselae in pompano fish. Pompano fingerlings collected from CMFRI, Vizhinjam was maintained at indoor glass tanks under the laboratory conditions for three days for acclimatization. Three groups of fish in duplicate were intraperitoneally administered with 50 ul of bacterial culture having inoculum strength of 2.75x107, 2.75x106 and 2.75x105 per fish after tenfold serial dilution. In the 7 day observation period, 85 and 80 % mortality was observed in the first two higher concentrations and no mortality was noticed in the control tanks and in lowest concentration administered tank. Bacterial reisolation from dead pompano fish tissues such as kidney, spleen, gill and liver was carried out. Reisolated bacterial colonies were identified by standard biochemical tests and 16S rRNA sequencing and ureC multiplex PCR. Tissues such as kidney, spleen, liver and gill from moribund fish samples were subjected to histopathological analysis.
Results indicated bacterial clustering and increased melanomacrophages in spleen, focal necrosis of spleen and glomerulonephritis in the kidney.