Fin Rot Disease & Treatment: The Ultimate Guide


Fin rot, in general terms, is an active infection involving the fins that as it progresses can cause the fins to “rot” away.  The most common cause of fin rot is trauma to the fish that disrupts their slime coat and external tissues leading to bacterial infections. These infections can have even secondarily fungal infections. Species that have delicate elongated fins are more prone to fin rot, as those fins are less likely to be fully used for propulsion through the water and therefore more likely to be hurt. Imagine trying to wear a long sheer scarf underwater while keeping the edges from brushing up against anything around you as you swim.  

Initial injuries may look red, white, or pink raised areas on their fins at first. As the skin starts to heal back the tissue may look white or translucent, which can be commonly mistaken for fin rot. In some cases it can also be caused by systemic infections. Individuals that have a compromised immune system or poor water quality are often more prone to infections. If left untreated, fin rot could even be deadly. 

The disease process itself is not contagious in the usual sense, but can be “passed” to another fish if they have direct contact to the infected tissue and the healthy fish has a compromise to their skin or immune system. As with every tank, being a closed system means your fish are essentially swimming around in their own toilet. Poor water quality management and tank maintenance are direct factors in healing and the risk of illness in general. Fin rot can be cured, but if persistent or severe can be difficult to resolve. Diseased tissue may or may not grow back depending on the severity. Make sure to involve your local aquatic health professional if you are seeing multiple fish affected or in chronic cases. 

Fin Rot Symptoms

Aside from monitoring for trauma in general, you may initially see the fin or tail start to show discoloration particularly around the edges. This may be white, red, or black. The fins then start to look frayed or uneven as the infected pieces rot and fall away. In the final stages of the disease, the entire fin or tail has been eaten away and the infection starts to attack the main body, which can be life threatening. Other common signs are decrease in appetite and/or activity. 

Fin nipping can be easily confused with fin rot to new aquarists. If you have noticed aggression in your tank make sure to closely observe the areas for color changes as mentioned above. While fin rot isn’t always caused by nipping, nipping can lead to fin rot. 

Fin Rot
Fin Rot

Fin Rot Treatment

Promoting factors that support a good immune system is basic care for almost all illnesses in aquatic pets. Catching the infection early will increase the likelihood of success for treatment.  In severe cases you may even want to consider starting over by isolating sick individual(s) and cleaning the tank completely and thoroughly before replacing them back into their habitat. If you have invertebrates in your tank, be very cautious prior to initiating any treatment, as they have different sensitivities than other animals in your system.

The first step in any aquatic health issue, is to confirm your water quality and the cleanliness of the tank. Discovering what environmental factors could be making your fish ill is crucial to the success of your treatment long term. Poor water quality can hinder the outcome of most aquatic diseases. Check for items in the tank that could traumatize individuals as they swim by and remove them as appropriate. Clean any item in the tank that may need attention and assess the cleanliness of your filter system. Full water changes can be stressful to your fish unless warranted. Routine partial water changes are less likely to cause large swings in the water chemistry and can help you a healthier tank long term.

Salt can be used to help treat fin rot and has some antiseptic properties. If you happen to have catfish, be aware that they can be very sensitive to salt levels. If you are using a higher concentration of salt this could also negatively affect any plants or invertebrates you may have in the system as well. For prolonged immersion a common dose is a teaspoon of salt per gallon. More concentrated salinity water bath for short 10-30 minute treatments may be another option.

 Always remember that regular iodized table salt is not appropriate for your fish tank. Commercially available aquarium salt is a better and safer choice. Salt will remain behind even with evaporation. Don’t forget slow, smaller water changes to reduce the salinity in your tank over time. It is safer to increase the salinity in the water incrementally if you find that lower concentrations are not quite adequate for the infection.

Antibiotic treatment is often saved for more severe cases, as they can have drawbacks. When given directly to the fish, for example in food or by injection, the medication may have a hard time reaching all the way to the tips of the fins due to the thinner tissue and vessels. When added directly to your tank they can wipe out your biological filtration which can cause spikes in the nitrogen cycle. Separate water bath treatments may be appropriate but should done under the guidance of an aquatic veterinarian.

Many antibiotic treatments are prescription only. One medication commonly used that is seen in pet stores is the antibiotic erythromycin, but most cases can be improved with a better environment alone. Your veterinarian may recommend other treatments in severe cases. Food fish have different regulations and restrictions on antibiotics, if this happens to in any way apply to you, consult a veterinarian before any treatment.

Fin Rot Prevention

Some of the best “treatment” is prevention. The same can be said of fin rot. Also, catching this disease process early on is more likely to yield better results.  Below we’ve listed some things to keep in mind to help prevent the rot. 

  • Proper quarantine for new additions prior to introduction to your system
  • Good (and consistent) water quality
  • Routine partial water changes for maintenance
  • Avoid overcrowding
  • Trim your aquatic plants as needed and avoid items that could snag your fish as they swim by
  • Monitoring for aggression between individuals 
  • Avoid over feeding and remove uneaten food when possible. 
  • Isolate sick individuals 

Regular system maintenance and cleaning are critical not only for the health of your fish but often make it easier for them to recover once ill. Avoiding trauma when possible will significantly reduce the risk of infection. 

How to tell if Fin Rot is Cured

Now that you’ve cleaned your tank, verified your water quality, isolated your sick fish, and treated it…how do I know it’s resolved? The tissue, if not severely damaged, often grows back but may be a different color than before. You may see your fish starting to eat better and be more active as it heals. Once resolved, there shouldn’t be any new lesions and the tissue should have regrown (unless too severe). To be on the safe side, monitor recovered individuals for some time before reintroducing them to the system to make sure no new lesions appear.

Betta Fish and Fin Rot

Betta fish often take longer rest periods than other species. They will need a smooth area for them to rest to help avoid injuries. Consider using betta fish specific decor. They also have long ornate tails more prone to injury.

Guppies and Fin Rot

Guppies also have long ornamental tails. Known to have a more voracious appetite these fish can produce more waste and quickly decrease water quality. Routine partial water changes and vigilant water quality are important.

Goldfish and Fin Rot

Many goldfish breeds have been bred for showy tails as well. When choosing substrate for your tank, take into consideration that goldfish are high waste producers and have a tendency to dig and root around in the substrate. Pick a substrate that is unlikely to injure them or be a choking hazard. If you prefer a minimalist appearance, consider no substrate at all.

Angelfish and Fin Rot

Angelfish fins are long and spread out, therefore more likely to injure. They also thrive in warmer temperatures which is more conducive to bacterial growth. Colder water temperatures may compromise their immune system.

Fish Laboratory

With decades of collective fishkeeping experience, we are happy to share the fish care tips that we've picked up along the way. Our goal at Fish Laboratory is to keep publishing accurate content to help fishkeepers keep their fish and aquarium healthy.

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