DIAGNOSIS OF AEROMONAS HYDROPHILA INFECTION IN FISH
Aeromonashydrophila causes disease in fish known
as "Hem-morhagicSepticemia", "Motile Aeromonas
Septicemia", "Ulcer Disease", or "Red-Sore
Disease". The many synonyms of this disease relate
to the lesions caused by this bacterium which includes
lesions of sep-ticemia when the bacteria or bacterial toxins
are present within numerous organs within the fish, and
ulcers of. the fish's skin. Aeromonashydro-phila is
a ubiquitous gram-negative, motile, rod-shaped' bacterium
which can be commonly isolated from fresh water ponds and
is also a normal inhabitant of the gastrointestinal tract
of fish. The disease primarily affects freshwater fish
such as catfish and bass, and many species of tropical
or ornamental fish.
Fish infected with Aeromonashydrophila may have
many different clinical signs. These range from sudden
death in otherwise healthy fish to inap-petence, swimming
abnormalities, pale gills, bloat and skin ulcerations. The
skin ulcers may occur at any site on the fish and often
they are surrounded by a bright red rim of tissue. Because
of the variability of these clinical signs, the diagnosis
of this disease based only upon the clinical presentation
of the fish is highly unreliable and may be economically
disastrous to the fish producer.
With intensive fish farming systems, whether these systems
are outdoor ponds or indoor aquaria and tanks, predisposing
factors are primarily responsible for the precipitation
of this disease. Stress is the single most important predisposing
factor associated with this disease. Stress is due to poor
management and/or poor water quality. Management factors
include:
nutrition, handling, transportation and over-crowding
of fish. Water quality must be excellent to prevent this
disease. This means that the dissolved oxygen (DO), pH,
temperature and alkalinity of the water must be satisfactory,
and that the ammonia, nitrite and COolevels must be kept
to a minimurn.
The best method, of diagnosis of this disease in fish is
by a positive bacteriologic culture of affected organs or
lesions and conformation of the characteristic lesions with
histopathology. Acutely affected, untreated, live fish are
the best samples to send to the ADDL for diagnostic purposes.
If you have questions about this disease, please give
me a call at (317)494-4770.
Randy White, DVM,PhD Veterinary Pathologist
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