Fin rot

Fin rot – symptoms, causes and treatment

Long finned veil tail betta with fin rot
Long finned veil tail betta with fin rot


Although this looks very much like a fungal infection, it is in fact caused by a bacterial infection of the fins. The most common bacteria involved are Aeromonas, pseudomonas and flavobacteria as in cotton wool disease.


Symptoms include split, frayed and “eaten away” fins usually having a white fluffy edge to the fins or dark markings.
Fin rot is brought on by fish that have become unwell because of stress, bad water conditions or fin-nipping by other fish.
Long-finned fish are more prone to fin-nipping for obvious reasons. Fin rot can also occur when long finned fish such as fancy goldfish are over wintered outside in cold ponds.


This comet goldfish has caught fin rot
This comet goldfish has caught fin rot

It is better to treat early before the bacteria spreads into the body.  If the disease has spread into the body then the fish is at risk of dying.
Use an aquarium anti bacterial medication by swabbing the fins with a cotton wool bud dipped in antibacterial solution. You can add salt to the water or methylene blue. This helps to lower the general level of waterborne bacteria.
It is very important to fix the conditions in the aquarium that caused the outbreak of fin rot in the first place. Try reducing overcrowding, remove excess fish waste and rotten food in the gravel, keep appropriate water temperatures for the fish and maintaining the filter media by removing excess accumulated waste. If it was caused by fin nipping then remove the aggressive fish or remove the fish that is suffering from fin rot.
If the condition persists or returns then try an antibiotic or antibacterial medication in the water. An alternative to an antibacterial in the water is salt in the water.

When the bacteria has been cured and the aquarium is clean, the fins will completely grow back in several weeks.

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