Aeromonas Infections 1
Aeromonas infections are caused by bacteria
Some strains of Aeromonas are more virulent,
which are present in the water all of the time.
which means that they possess special properties
Usually, when fish get sick with an Aeromonas
which enable them to cause more serious disease
infection, something has happened to make them
outbreaks. If these more damaging strains become
susceptible to bacterial invasion. There are several
endemic in a population of fish (which means that
species of Aeromonas which can infect fish. The first
they are there all of the time and the fish develop an
is Aeromonas salmonicida, which causes a disease
immunity to them), it becomes difficult to introduce
called furunculosis in salmon and trout. This bacteria
new fish into the water body without suffering major
is not usually of concern for producers of warmwater
fish and will not be discussed further in this publication. The two species of Aeromonas which do
Signs of Aeromonas infection
cause disease in warmwater fish are Aeromonas
There is no single physical or behavioral sign
hydrophila and Aeromonas sobria. The difference
specific for Aeromonas infections. Infected fish
between these two bacteria is of greater interest to
frequently have: small pinpoint hemorrhages at the
scientists than of practical importance to producers;
base of the fins or on the skin, distended abdomens,
thus, they will be referred to collectively as
and protruding eyes. Internal signs include: fluid in
Aeromonas infections or Motile Aeromonas
the abdomen, swollen liver and spleen, and the
intestines are distended and fluid-filled.
Aeromonas infections are probably the most
common bacterial disease diagnosed in cultured
Submission of suspect fish to a
warmwater fish. Usually, mortality rates are low
diagnostic laboratory
(10% or less) and losses may occur over a period of
It is important to submit fish suspected of being
time (2 to 3 weeks or longer). In these instances,
infected with Aeromonas to a diagnostic laboratory to
some factor; usually stress, has caused the fish to
confirm the disease, and to determine the antibiotic
become more susceptible to the bacteria. Common
sensitivity of the strain of Aeromonas causing the
sources of stress are poor water quality,
problem. In addition, because Aeromonas is a
1. This document is FA14, one of a series of the Fisheries and Aquatic Sciences Department, Florida Cooperative Extension Service, Institute of Food and
Agricultural Sciences, University of Florida. Original publication date June, 1991. Reviewed July, 2002. Visit the EDIS Web Site at http://edis.ifas.ufl.edu.
2. Ruth Francis-Floyd, IFAS Extension Veterinarian, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida,
The Institute of Food and Agricultural Sciences (IFAS) is an Equal Employment Opportunity - Affirmative Action Employer authorized to provide research, educational information and other services only to individuals and institutions that function without regard to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For information on obtaining other extension publications, contact your county Cooperative Extension Service office. Florida Cooperative Extension Service / Institute of Food and Agricultural Sciences / University of Florida / Larry R. Arrington, Interim Dean
stress-mediated disease, it is not unusual to find that
infected fish are heavily parasitized or concurrently infected with another systemic disease agent. Contact
your county extension agent for assistance and
common bacterial disease, caused by Aeromonas,
information on where and how to submit samples for
which affects warmwater fish, both in commercial
production systems and in natural waters. Frequently, MAS outbreaks are stress-related and elimination of
Management of an Aeromonas
the underlying stress factor may be sufficient to
outbreak
resolve the disease outbreak. It is important to run antibiotic sensitivity tests prior to using antibiotics
When MAS, or any bacterial infection, is
for controlling Aeromonas outbreaks. Many strains of
suspected in your fish, you should immediately
Aeromonas are resistant to commonly-used
submit a live, sick fish to the nearest diagnostic
antibiotics, and it is important to determine which
facility. If Aeromonas is diagnosed, you need to
drug should be used before spending time and money
know what legal drug the isolate is sensitive to and
whether or not other infectious agents are present. There are two antibiotics legal for the treatment of
Anytime an Aeromonas infection persists as a
bacterial diseases of channel catfish. Both of these
chronic problem, it is important to make an effort to
are administered in the feed. The first, Terramycin,
determine if an underlying stress factor is causing the
has been available for many years and many strains
fish to have insufficient immune protection from the
of Aeromonas are resistant to it. If the bacteria is
bacteria. Evaluate the water quality, nutrition,
resistant to the drug then there is no benefit attained
handling, and use of drugs and chemicals.
by feeding that medication. Terramycin~, an
Deficiencies in any of these areas could predispose
oxytetracycline product, is available in sinking feed
fish to Aeromonas infections. Cleanliness and good
only, and is fed for 10 days followed by a 21-day
management practices will reduce Aeromonas
withdrawal time. The other product, Romet-30 , a
potentiated sulfonamide, has only been available since 1985. It is available in a floating feed, and is fed for 5 days, followed by a 3-day withdrawal period. The withdrawal period is the time you need to wait after feeding the medicated feed for the last time until the fish can be sold for human consumption.
In many cases, it may not be necessary to treat
Aeromonas infections with medicated feeds. For example, if fish are heavily parasitized, they may resist the bacterial disease if the parasites are removed. Similarly, if disease susceptibility is attributed to poor water quality, then correction of the basic husbandry problem could result in a resolution of the bacterial disease outbreak. Keep in mind that the purpose of antibiotics is to keep disease-causing bacteria at bay long enough for the fish to heal itself. In addition, if the affected system is an indoor or closed system, good sanitation is essential to decrease the number of bacteria in the system.
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