Fin Rot: Everything you need to know

Fin rot is a bacterial infection that can affect a variety of aquarium fish by attacking the fin of the fish. This disease is usually caused by a number of conditions which may include; a dirty tank, overcrowded fish in a tank, and various other environmental factors. Fortunately, the condition can easily be prevented as long as the basics of aquarium fish care followed to the latter. While preventing fin rot is easy, it must be understood that once it sets in, it may be very difficult to treat especially if it has gone into the more advanced stages. To make matters worse is that if the disease is left untreated, the affected fish will ultimately die. If this occurs, there is a big chance that all the other remaining fish in the tank may also get infected with the disease.

Fin Rot


There are various identified causes of this health condition that affects aquarium fish. While it is a bacterial disease that mostly affects freshwater aquarium fish, it may also be a sign of another serious health problem of fish in the tank.


The one major culprit that causes this health condition in fish is a gram positive bacterium. The disease may be spread by other infected fish to healthy fish in the aquarium. Infected fish may spread this disease to healthy fish in the tank through physical contact. In other instances infected aquarium water may also spread the disease to healthy fish in the tank.

Also feeding your fish with expired food and leaving large amount of food debris floating on the aquarium can also cause the disease.

Other fish

There are also other cases where another fish may nip the tail of a healthy fish. The fish with the nipped tail thus may easily get an infection which may develop into fin rot.


Putting too many fish in a small tank risks the fish to the disease. What happens in a crowded fish tank is that water quality becomes poor. The pH also fluctuates uncontrollably and the levels of nitrates and ammonia from the waste of fish will also increase.


When the water temperature in the aquarium is too cold, it could expose the fish to the disease. This therefore calls for the tank owner to be able to have a check on the temperature of the tank on a regular basis.


Stress has also been linked with causing fin rot in aquarium fish. Your aquarium fish may get stressed when you play with them by handling them frequently or moving them to other tanks inappropriately. There are some aquarium fish species that are dominant and territorial and their presence may cause stress to less dominant fish there. This explains why it may be best to just place fish of the same breed or species in one aquarium and not mix with other types of fish that may be aggressive, dominant and territorial.

Fin Rot symptoms

  • the fin edges may turn white
  • the bases of fins may appear inflamed
  • entire fin will rot away
  • the fins will fray

During the early stages of fin rot, usually the fins of the fish will show discoloration and may appear milky particularly on the edges. This sign is usually hidden and may go unnoticed up until when the fraying of the tail fin occurs. With the infection spreading on the fin, small parts of the fins will die and start to fall off thus leaving a ragged edge on the fin affected.

Mostly affected area on the fin will be inflamed and appear reddish with bloody patches showing with more tissues being eaten off by the bacteria. If this is left to continue without any remedy offered, the entire fin may simply just rot away.


As the saying goes prevention is usually better than cure this should be the case with your aquarium fish. It is best to be cautious when you are buying new tropical fish to introduce to your aquarium. It is usually advisable to examine thoroughly the fins and tails of the fish before you introduce them into the aquarium. If you notice any of the sings noted above on the fish it is best to avoid them and not introduce the fish into your aquarium.

Another way to prevent the disease from occurring in your aquarium is to check for any possibility of fin nipping. If you notice it is occurring in your aquarium, it is best to separate the fish because the fish that have nipped fins may easily catch infection.

Also as we have earlier observed that aquarium water is also another cause of the disease it may best to change aquarium water frequently. Ensure that you use clean water in the aquarium as this helps to keep bacteria that causes the disease at bay. Basically, the frequency that you will need to be changing the aquarium water will depend on the size of the tank and the fish population in it. Please note that water that has got high levels of nitrates and ammonia provide a conducive environment for bacterial growth in the tank!

Again if you notice fish that has shown signs of fin rot, the best thing to do is to isolate it from the rest of the population. You will then need to replace the aquarium water with immediate effect to prevent infection of other fish in the aquarium.

Last but not least, always ensure that the temperature and pH of the aquarium water is always kept at the optimum.


Because fin rot is a bacterial infection it can be treated with good antibiotics. It is best to treat the disease with antibiotics that are broad spectrum and will eradicate gram-negative micro-organisms.

Use of aquarium salt may be productive for live bearing fish but should be avoided if the fish in the aquarium are scaleless catfish. These kinds of fish are usually very sensitive to salt and the result may be catastrophic.

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