1. Aeromonas infections are probably the most common bacterial diseases diagnosed in fish ponds.
2. There are some six species of Aeromonas.
3. Aeromonas hydrophila is the most common.
4. This bacterium is common in all aquatic environments.
5. Because of Aeromonas hydrophila’s structure, it is very toxic to many organisms.
6. It is known as a pathogenic bacterium. (A disease causing bacteria).
7. When it enters the body of its victim, it travels through the bloodstream to the first available organ. It produces Aerolysin Cytotoxic Enterotoxin (ACT), a toxin that can cause tissue damage.
8. Usually, when fish get sick with an Aeromonas infection, something has happened to make them susceptible to bacterial invasion therefore they are considered “opportunistic pathogens,” - meaning they only infect hosts with weakened immune responses.
9. Common sources of stress in fish ponds are poor water quality, overcrowding, or rough handling.
10. This opportunistic bacteria causes havoc when a fish is already infected with a virus or another bacterium.
11. It is hardy and a resistant bacterium. Chlorine, refrigeration or cold temperatures have very little effect on it.
12. Fish infected with Aeromonas hydrophila develop hemorrhagic septicaemia. Hemorrhagic septicaemia causes lesions that lead to scale shedding, haemorrhages in the gills and anal area, ulcers, pop eye (exophthalmia or protruding eyes), and abdominal swelling.
13. Other possible signs of Aeromonas infection are
a. tail and / or fin rot
b. small pinpoint haemorrhages at the base of the fins or on the skin
c. distended abdomens
14. Internal signs include: fluid in the abdomen, swollen liver and spleen, and the intestines are distended and fluid-filled. Facts You Must Know:
Some strains of Aeromonas are more virulent than others as which means that they possess special properties which enable them to cause more serious disease outbreaks.
If these more damaging strains become endemic in a population of fish (they are there all of the time and the fish develop immunity to them), it becomes difficult to introduce new fish into the water body without suffering major losses of newly-stocked fish.
For successful treatment it is vitally important to submit fish suspected of being infected with Aeromonas to a diagnostic laboratory to confirm the strain, AND most importantly to determine the antibiotic sensitivity of the strain of Aeromonas causing the problem.
In addition, because Aeromonas is a stress-mediated disease, it is not unusual to find that infected fish have heavy parasite infections or have more than one type of disease infection.
It is important to run antibiotic sensitivity tests prior to using antibiotics for controlling Aeromonas outbreaks. Many strains of Aeromonas are resistant to commonly-used antibiotics, and it is important to determine which drug should be used before spending time and money on an ineffective product.
Lab Example 1:
Example 1 is a lab test result. Note the bacterial infection has been identified as Aeromonas and this strain of Aeromonas bacteria from this particular pond is sensitive to the first anti biotic tested on the list. It is however resistant to a commonly used anti biotic – tetracycline. Note that two different types of Aeromonas have also been found.
Lab Example 2:
Another lab test result. Note the bacterial infection has again been identified as Aeromonas and it has a completely different resistance and sensitivity to the strain of Aeromonas in example 1 above.
Lab Example 3:
Interesting in that this pond has three different strains of Aeromonas and each of the three strains has a different antibiotic sensitivity and resistance.
The Way to Go:
If the bacteria is resistant to the drug then there is no benefit attained by feeding or administration that medication.
The critical point here is the strain of Aeromonas has been identified and the sensitivity or resistance to specific antibiotics has been identified.
IF the correct laboratory diagnosis was done and the correct antibiotic is used there is a very good chance of success and recovery of the fish.
Anytime an Aeromonas infection persists as a chronic problem (see the various symptoms above), it is important to make an effort to determine if an underlying stress factor is causing the fish to have insufficient immune protection from the bacteria.
Evaluate the water quality, nutrition, handling, and use of drugs and chemicals. Deficiencies in any of these areas could predispose fish to Aeromonas infections.
Cleanliness, regular maintenance and good management practices will reduce Aeromonas outbreaks in your koi pond.