Fin Rot


Fin rot is a symptom of disease or the actual disease in fish. This is a disease which is most often observed in aquaculture, but can also occur in natural populations.

Fin rot can be the result of a bacterial infection (Pseudomonas fluorescens, which causes a ragged rotting of the fin), or as a fungal infection (which rots the fin more evenly and is more likely to produce a white ‘edge’). Sometimes, both types of infection are seen together. Infection is commonly brought on by bad water conditions, injury, poor diet, or as a secondary infection in a fish which is already stressed by other disease.

Fin rot starts at the edge of the fins, and destroys more and more tissue until it reaches the fin base. If it does reach the fin base, the fish will never be able to regenerate the lost tissue. At this point, the disease may attack the fish’s body directly.



Fin rot is fairly easy to diagnose, though ideally you want to catch it when the disease has barely progressed as it will be much easier to treat. Such symptoms for fin rot are:

  • Fin edges turn white
  • Fins fray
  • Base of fins inflamed
  • Entire fin may rot away or fall off in large chunks


Fin rot is caused by one of several gram negative bacteria. Several antiboitics are effective, however the root cause must be addressed as well.

Fin rot occurs when the fish is stressed for some reason. The most common cause is poor water quality. Overcrowding the tank, feeding outdated food or overfeeding, and moving or handling the fish can also cause stress leading to fin rot.

Treatment should include a water change, and careful examination of the aquarium conditions. If there is food debris, vaccumm the gravel and take care to avoid overfeeding. Start dating your fish food, as it loses the vitamin content fairly quickly after it is opened. Feeding fish fresh, high quality food, in smaller quantities is far better than frequent large feedings of stale foods.

Check the pH and water temperature of the water, and make sure it is appropriate for your fish. Incorrect pH is very stressful for fish, and can lead to disease. Low water temperatures, particularly in fish with long flowing fins, can trigger fin rot.

If the root cause is corrected, antibiotics will usually cure the disease itself. Use a drug that is effective against gram negative organisms. Chloramphenical, Oxytetracycline, and Tetracycline, are good choices. Treat according to manufacturers instructions.

The use of aquarium salt will benefit livebearing fish, but should be avoided in fish, such as scaleless catfish, that are sensitive to salt.