Fin rot (tail rot or gill rot) is a common disease caused by bacterial infection in aquaria and aquaculture due to poor water condition.

Symptoms: In case of Fin rot, bacteria eats away the delicate membranes of fish. Fin rot starts at the edge of the fins, and destroys more and more tissue until it reaches the fin base. If it does reach the fin base, the fish will never be able to regenerate the lost tissue. At this point, the disease may attack the fish's body directly.Usually the area of the damaged fin becomes opaque and white then is eaten away by the bacteria. Edges of fins start to rot away. Often fungus develops on the infected area giving the wound a fluffy appearance in the beginning, however eventually the fin will disappear and if un treated the fish will die.

Causes: Fin rot are caused by gram negative bacteria (Aeromonas, Pseudomonas & Vibrio anguillarium. These bacteria, like many others is usually present in small quantities in the tank but regular water changes and feeding good quality food to your animals will usually keep these bacteria under control.

Aeromonas:(Aeromonas hydrophila and Aeromonas sobriais) are a gram-negative bacteria.

Pseudomonas: is a gram-negative bacteria. This bacteria is also responsible for “red leg” disease in amphibians

Vibrio anguillarium: These bacteria attacks the gastrointestinal tract, causing Ulcers in fish body. Most cases the fish will loose it appetite with red spots on the ventral and lateral areas. It can also cause cloudy eye, leading to pop eye and complete eye loss. These bacteria usually attack multiple fish together, grows very rapidly and in many cases the fish will die without showing symptoms.

Treatment: Usually easy to treat if caught early enough.Any gram-negative anti-bacteria treatment will kill these bacteria and can recover from fin rot. In case you see symptoms of fin rot:

--> Perform a 50% water change as soon as possible and then watch the water quality at least for 2-3 weeks
--> A treatment of potassium permanganate will reduce the level of organic material suspended in the water and will therefore help to reduce levels of bacteria.
--> A 1% solution of salt will help destroy bacteria like Pseudomonas. However before adding any salt check if the species of fish can tolerant it.
--> Antibiotics like Oxytetracycline or Erythromycin which kill gram-negative bacteria. There are many commercial medicines available

Prognosis: If the fish with fin rot left untreated, bacteria like Saprolegnia develops on the decaying areas of the fish. Saprolegnia is spread by spores through the air and causes fungal infections in injured or sick fish or amphibians, and often attacks eggs, killing them before they can hatch. It left un-treated, this fungus spreads and eventually kills the fish/animal.

Saprolegnia: this is an aquatic fungus (often called a 'mould') commonly found in aquariums, particularly where there is an abundance of decaying organic matter.

Prevention: Maintaining water quality is always extremely important. It should always be checked first, because it is often the cause of disease in aquarium fish.

--> Frequent water changes can work to prevent the spread of disease by "watering down" the concentration of disease agents, and by reducing stress on the tank occupants. All tanks need a 10-25% water change on a weekly basis. The best method of changing water is siphoning the water from the bottom, removing debris and fecal matter from the gravel.
--> Poor quality food or stress leading to a suppressed immune system in the animal. Always feed fish from reliable sources and use high quality a range of food. This will help to develop a healthy immune system to fight off infection.
--> Do not over feed your animals. The bacteria eats uneaten food and grow rapidly on them.
--> Adding bogwood significantly reduces fungus and bacterial disease in your aquatic animals.
--> Using a regular waste control bacteria media to reduce uneaten organic material on the substrate. Remove old or dying plants so that they do not rot and cause debris on which bacteria can grow
--> Regular substrate maintenance. Consider setting up a soil based substrate to limit the bacteria numbers.

References:

Wikipedia - Fin rot
TheAquariumWiki - Fin Rot

Good Luck,

Deepak

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