The two most common bacteria that cause problems on koi fish are Aeromonas and Pseudomonas. Both of these bacteria are naturally occurring and are found in all pond and lake water. These bacteria are non existent in tap water because chlorine is added to kill any bacteria. Never the less, you can start up a brand new pond with tap water and within 3 weeks after the chlorine has evaporated, you will find at least a low level of these bacteria in your water.
Normally, in a clean healthy pond, the levels of bacteria are so low that they will not cause a problem on their own. The outer slime coat or epidermis normally protects the fish from these harmful bacteria. The most common reason koi experience a bacterial infection is when their slime coat or epidermal layer is broken and the bacteria is allowed to infect the koi. These sores can grow very quickly if they are not treated.
Columnaris (Flexibacter columnaris) or Cotton Wool Disease is another bacterial infection. The common name comes from the white tufts that develop around the mouth and spread to the body and fins, often leading to ulcers and a thin appearance.
Often mistaken for a fungal infection because of its...(for more details - click on product image)
Raised scales (rather like a pine cone) and eyes standing out from the head.
Dropsy itself is not a disease, but rather a result of some other cause. Dropsy is a term given to the swelling that occurs internally in the fish. There are multiple possible causes. Sometimes it's not contageous, but sick...(for more details - click on product image)
A number of bacteria are associated with finrot, lesions and internal hemorrhaging, notably Aeromonas and Pseudomonas. Ulcers usually start at the site of an injury, the bacteria then infect it causing further damage, and fungal infection can also occur.
Such holes result in osmoregulatory problems,...(for more details - click on product image)