Aeromonas hydrophilia, also called ulcer disease or just Aeromonas, is the number one killer of Koi. It does not kill nearly as fast as a virus like KHV, but if not treated, a Koi will usually eventually succumb to the disease. Aeromonas is always present in water, it is also an opportunistic bacteria. Koi will only get an infection if something else has harmed them in any way, especially if portions of their slime coat have been stripped away. Aeromonas and Pseudomonas usually exhibit the same symptoms. The skin ulcer will grow bigger and bigger until muscle tissue is exposed. After that, the infection turns septic and spreads throughout a Koi in their blood stream. The kidneys usually fail next and then a Koi's ability to osmoregulate fails. This causes the condition known as dropsy, or pine cone disease. The Koi will expire, usually within two weeks as more and more bodily functions fail. Nowadays, many strains of Aeromonas are very resistant to antibiotics. This is due to the abuse of antibiotics by the Koi breeders over the years, so they could lower mortality rates, and then increase profit.
Aeromonas infections are caused by bacteria which are present in the water all of the time. Usually, when fish get sick with an Aeromonas infection, something has happened to make them susceptible to bacterial invasion. There are several species of Aeromonas which can infect fish. The first is Aeromonas salmonicida, which causes a disease called furunculosis in salmon and trout. This bacteria 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 cause disease in warmwater fish are Aeromonas hydrophila and Aeromonas sobria. The difference between these two bacteria is of greater interest to scientists than of practical importance to producers; thus, they will be referred to collectively as Aeromonas infections or Motile Aeromonas Septicemia (MAS).
Aeromonas infections are probably the most common bacterial disease diagnosed in cultured warmwater fish. Usually, mortality rates are low (10% or less) and losses may occur over a period of time (2 to 3 weeks or longer). In these instances, some factor; usually stress, has caused the fish to become more susceptible to the bacteria. Common sources of stress are poor water quality, overcrowding, or rough handling.
Some strains of Aeromonas are more virulent, 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 (which means that they are there all of the time and the fish develop an immunity to them), it becomes difficult to introduce new fish into the water body without suffering major losses of newly-stocked fish.
Signs of Aeromonas infection
There is no single physical or behavioral sign specific for Aeromonas infections. Infected fish frequently have: small pinpoint hemorrhages at the base of the fins or on the skin, distended abdomens, and protruding eyes. Internal signs include: fluid in the abdomen, swollen liver and spleen, and the intestines are distended and fluid-filled.
Aeromonas Infections Antibiotics
), quinolones, third generation cephalosporins, and aminoglycosides are all effective treatments.