Ornamental karp, or koi, are among the most popular fish in the tank. They bring great enjoyment, but owners should be wary of a potentially fatal disease that many fall prey to. Koi ulcerative disease is a bacterial infection caused by the bacteria called aeromonas salmoncida. It can be treated by antibiotics, although even then your fish may end up scarred. The best medicine for the disease is to prevent it by following some basic tank maintenance procedures.
Koi ulcerative disease is particularly prevalent during the spring and fall months, and it frequently crops up within a month of introducing of new fish to the pond or aquarium. Affected fish usually have shallow or deep ulcers somewhere on the body or exhibit pop-eye, bloody spots and a distended abdomen. These ulcers can expose the fish to invasion by other illnesses and are likely to result in death if left untreated.
Your veterinarian may be able to diagnose the disease through bacterial tests and by studying the history of your fish and its clinical signs. When the condition is identified early, and the fish are treated appropriately with antibiotics, the prognosis is fair to good, although surviving fish may have permanent scars. When possible, injectable antibiotic treatment of clinically affected fish, along with oral treatment of other fish in the pond or aquarium, is recommended. Make sure to administer only those antibiotics that are prescribed and do so only under the direction and supervision of a licensed veterinarian who has examined your fish.
The best way to prevent koi ulcerative disease is to quarantine new aquarium pond fish for at least one month. This practice, at the very least, should identify infected fish before they have a chance to spread this bacterial disease to your established fish population. Other important preventative steps include maintaining excellent water quality, performing frequent water changes (at least 25 percent each month), not overcrowding your aquatic system and maintaining steady temperatures and an adequate air supply.