Fin Rot on a Goldfish

Goldfish are the descendants of a wild carp fish, known as the Prussian or Gibel Carp (scientific name: Carassius Gibelio). They were one of the first domesticated fish, originally bred in China and then spread around the globe via trade. Because of their low maintenance and tolerant diet, goldfish are a popular first pet -- but they are not without complications. Fin rot is a common ailment of the goldfish that worries many owners. Fortunately, you can treat the diseases that cause it if you discover them early enough.

  1. What is Fin Rot?

    • Many people mistakenly call fin rot a disease. Actually, it is a symptom of one or more diseases that commonly affect goldfish. Fin rot generally begins as a slight raggedness to the tail fin, but as it progresses, the tail develops tears and rips and the dorsal fin begins to show signs of wear. Occasionally, the edges of the damaged areas will display fuzzy white cottony tendrils. In the later stages, the diseases that cause fin rot manifest as redness to the skin and progress into the flesh of the fish.

    What Causes Fin Rot?

    • The aquatic environment where fish swim is naturally teeming with bacteria and microorganisms. You can also find these organisms in the best-maintained fishbowls and aquariums. They generally cause problems to fish unless the fish is subjected to stress or injury. Aeromonas, Pseudomonas or Flexibacter bacteria are the most common bacterium responsible for fin rot. A water mold called Saprolegnia is also responsible for many observed cases. Sometimes bacteria and water mold work together to contribute to this disease.

    Treatments for Fin Rot

    • You can treat early fin rot by applying a number of dyes such as Malachite green, Methylene Blue or Potassium Permanganate daily to the affected regions of your goldfish until the symptoms cease. In advanced cases, you can feed antibiotic food to your fish or add specialized treatments to the water itself. You can add tetracycline to the aquarium's water to control bacteria or formulated fin rot salts to minimize the effects from water molds.

    Preventing Fin Rot

    • While it is good that so many remedies exist to counter fish rot, the diseases that cause it can be fatal in many cases. Fortunately, prevention of fin rot requires only a few precautions. The first and likely most important step is to keep the stress of your fish low. This means providing your fish with a place to hide and exposure to consistent day/night cycles. Water maintenance is an important preventative as well. Bi-monthly water changes and water filtration are especially vital to maintaining goldfish health. Other ways to reduce risk of fin rot include keeping fish populations low and maintaining proper diet.