As a gram-negative bacterium, Aeromonas hydrophila, as a major
pathogen in almost all animal taxa, produces intestinal inflamma-
tion in fish and induces high mortalities in a wide range of fish
species at different stages ofgrowth [ !~3 |. Currently, the bacterium
is regarded as one of the major problems in carp aquaculture,
causing considerable economic losses in aquaculture industry
worldwide [4—6]. Several studies in fish have found that
A. hydraphilu enters the fish body via the gills and damages skin [7],
and results in the symptoms that include swelling of tissue, dropsy,
red sores, necrosis, ulceration, and hemorrhagic septicemia [S].