Fin Rot Cause, Detection, and Treatment

How to Diagnose, Prevent, and Treat the Common Aquarium Disease Fin Rot

Betta fish
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Fin Rot is one of the most common, as well as most preventable, diseases in aquarium fish. Although it is caused by several types of bacteria and often occurs concurrently with other diseases, the root cause of Fin Rot is always environmental in nature. Fish stress is also a contributing factor in Fin Rot. When fish are moved, subjected to overcrowding, or coupled with aggressive fish that chase and nip at their fins, they are more susceptible to Fin Rot.

Fin Rot can be difficult to cure, particularly in the more advanced stages. If left untreated, it will eventually kill the diseased fish and infect all the other fish in the tank as well.


  • Names: Fin Rot, Tail Rot
  • Disease Type: Bacterial (gram-negative organism)
  • Cause / Organism: Aeromonas, Pseudomonas  fluorescens, or Vibrio


  • Fin edges turn white
  • Fins fray
  • Bases of fins inflamed
  • Entire fin may rot away

In the early stages of Fin Rot, the edges of the fins will discolor, appearing milky colored on the edges. Often this change is so subtle that it goes unnoticed until fraying of the fins or tail begins. As the infection spreads, small pieces of the fins die and begin to fall off, leaving a ragged edge. Over time the fins become shorter and shorter as dead flesh continues to slough off the affected fins. The affected area may become red and inflamed; with bloody patches appearing as more tissue is eaten away.

It is common for secondary fungal infections to develop along the raw edges of the fins. It is not unusual for Columnaris (cotton-wool) to also be present at the same time as Fin Rot, as occur from environmental factors.


  • Correct root cause
  • Water change
  • Treat with antibiotics
  • Addition of aquarium salt

    Fin rot is caused by one of several gram-negative bacteria. Several antibiotics are effective; however, the root cause must be addressed as well to ensure the disease doesn’t return.

    The disease occurs when the fish become stressed by something in the environment. The most common causes of Fin Rot are poor water quality and improperly low water temperature. Overcrowding the tank, feeding outdated food or overfeeding, and moving or handling the fish can also cause stress leading to Fin Rot.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, vacuum the gravel and take care to avoid overfeeding in the future. Start putting dates on 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 often trigger Fin Rot.

    Once the root cause is corrected, antibiotics will usually cure the disease itself.

    Treatment with a drug that is effective against gram-negative organisms is recommended. The drugs Chloramphenicol, Oxytetracycline, and Tetracycline are good choices. Always treat according to manufacturer’s instructions, as the preparations can vary from manufacturer to manufacturer. It is particularly important to continue treatment for the length of time recommended, as ending treatment too soon can result in a re-occurrence of the infection.

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


    • Maintain good water quality
    • Perform regular tank maintenance
    • Keep proper water parameters
    • Feed fresh food in small amounts
    • Feed fresh food in small amounts

    The best prevention against Fin Rot is good aquarium maintenance.

    Change the water regularly, vacuum the gravel, and monitor the water chemistry by having a regular testing schedule, and documenting the results. This will allow you to quickly notice water chemistry changes that occur over time, giving you a chance to correct problems before they become serious. Do not overcrowd the tank, and watch for signs of fighting between fish.

    When feeding, keep the volume low. Overfeeding is the most common mistake made by all fish owners, and contributes to poor water quality. Be sure to use fresh foods. If the can has been open for half a year, it has lost most of its nutritional value. Purchase food in small enough containers that it can be used in one to two months.

    Take care when choosing tank mates for fish that have long flowing fins, as fin nipping leaves fish more susceptible to Fin Rot. It is also important to keep water temperatures warm enough for fish with long fins, as low water temperatures will promote Fin Rot in long finned species of fish.