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Fin Rot Disease, Symptoms, Causes And How To Treat It

Updated on March 9, 2014

The term Fin Rot (or Tail Rot) generally describes an affection of the tropical fish that results in a loss of tissue.

The attack usually begins in the border of the fins, and very occasionally a hole can appear in the middle of the fin.

The disease appears if a number of environmental factors and a significant amount of microbial agents are given.

Fin rot is a bacterial disease involving opportunistic bacteria such as Aeromonas, Pseudomonas or Flexibacter that abound in all aquatic environments.

Although the fin rot disease is caused by a family of bacteria, we should look for the true cause in the conditions of the environment. The appearance of this disease is an indication that the fish are not in good condition.

Appears when the fish have low defenses due to being suffering some kind of stress.

Fin Rot Disease
Fin Rot Disease
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It is difficult to diagnose the disease at the beginning because there are hardly any visible symptoms, only the edge of one or more fins becomes opaque.

In general this disease begins in the caudal fin. The opacity of the edge of the fins has two stages:

  • A slight opacity little perceptible in a sector of the edge of the affected fin (beginning of the bacterial colonization)
  • A whitish cloud, which covers a bigger sector or the whole edge of the affected fin (fish's defense against the attack)

Soon the opacity becomes a well-marked white line that cover the soft tissue from the edge of the fin. This line is the disintegration of the attacked tissue and an increase of the epithelial secretion produced by the immune system of the fish.

The fins are altered from outside to inside. As the disease advances the fin it is destroyed irregularly, as fringes.

Pathological Physiology

When fish are infected, the following signs can be observed:

  • Skin: There will be necrotic lesions on the skin. In a day or two these will transform into ulcers caused by the bacteria decaying the underlying tissue.
  • Gills: Lesions and ulcers also occurs in the gills. They are difficult to observe at least in the early stages. The progression of these ulcers, causes the fish to have great trouble with its respiration.
  • Behavior: The fish will become very listless and lethargic. On occasion, the fish will rest on the bottom of the tank. Reluctance to feed is very typical and the fish will become anorexic. Respiration is often rapid due to the damage done by the infection to the gills.
  • Fins: Large milky patches can be seen on the fins of the fish. One typical sign is the appearance of a saddle shaped lesion usually around the area of the dorsal fin. Saddle Back Disease is often used in aquaculture to describe this infection.

Causes Of The Disease

Two conditions should happen so that the illness takes place:

  • An alteration should take place in the environment so that the microorganisms become pathogenic
  • An imbalance should take place in the immunologic system of the fish

Changes in the environment:

  • Low temperature of the water
  • Significant temperature variations in a short time
  • Improper pH (excessively acid or alkaline)
  • Excessive presence of organic matter in the water (increase in the population of microorganisms)

Alterations in the fish:

  • Not cured wounds
  • Lack of folic acid
  • Stress or fear
  • Overpopulation

However, the most frequent causes of the disease are the introduction of sick fish or poor environmental conditions.


Water quality plays a vital role in the prevention and cure of this disease. Prior to initial dosing of any medication, a large water change (30-50%) with a thorough gravel cleaning in order to remove excess detritus and waste from the substrate should be performed.

Because the disease is of bacterial origin, treatment relies on antibiotics. There are several medications in the marketplace. As different producers use different concentrations follow,s the manufacturer's instructions for treatment.


The fin rot disease is highly preventable. As mentioned, is an opportunistic disease, waiting for favorable conditions to attack. The key is to keep the aquarium in good condition for this:

  • Ensure the quality of the water so that the fish are well
  • Reproduce the conditions of temperature, pH and water hardness suitable for the species
  • Avoid the excess of organic matter
  • Avoid decorations that can damage the fish
  • Change the water frequently
  • When introducing new fish, observe a period of quarantine


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