Flavobacteria Infection in Fish

By PetMD Editorial on Mar. 2, 2012

Bacterial Gill Disease in Fish


Aquarium fish sometimes suffer from a disease complex called bacterial gill disease. Although it most often affects young fishes, especially salmonids, it can affect any type of aquarium fish.  




Because the gills are primarily affected, fish suffering from bacterial gill disease will have respiratory problems, with visibly rapid or labored breathing and swimming close to the surface of the water as if trying to get air. They will show signs of a lost appetite, with little to no eating. The gills will often — though not always — show signs, with swelling, redness within the gill tissue, and deformed gills. The gills may have patchy growth of bacteria on them and a blotchy appearance. Without treatment, the gill and fin tissues will deteriorate and necrotize.




Bacterial gill disease typically occurs as a result of poor living conditions, such as overcrowding, poor water quality, high organic debris, increased temperature of the water, and increased ammonia levels. While it is most often the young and/or weak fish that contract the disease, due to their vulnerable immune systems, gill disease can affect fish of any age.

The bacteria that cause gill infections are primarily Flavobacteria, Aeromonas and Pseudomonas spp. The direct initiating cause by these bacteria is not conclusive, but they will often be found as secondary, opportunistic infections.




Bacterial gill disease must first be treated with a change in the living conditions of the fish. If they are crowded, they will need to be given more space, either in a larger aquarium, or separated into different aquariums. The cleanliness of the water and aquarium is paramount. A treatment of potassium permanganate and salt water additives can be used to help the fish heal and recover from the infection. The amount of salt you will use will depend upon the species you are treating, but it must be a salt that is specifically made for fish water, and it should only be in the prescribed amount. Antibiotic therapy may be used to treat secondary bacterial infections.




The best way to prevent bacterial gill disease from occurring is by maintaining hygienic living conditions for your fish. Keeping the water clean of organic debris, giving the fish plenty of space in which to move, with no overcrowding, maintaining a consistent temperature, and testing the water quality regularly to ensure that it is balanced are all the best practices for keeping your fish healthy and stress free. Additionally, filters should be changed every month or checked according to the filter manufacturer's directions. 


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