Fin rot is a symptom of disease

Disease

A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...

 or the actual disease in fish

Fish

Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

. This is a disease which is most often observed in aquaria

Aquarium

An aquarium is a vivarium consisting of at least one transparent side in which water-dwelling plants or animals are kept. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, marine mammals, turtles, and aquatic plants...

 and aquaculture

Aquaculture

Aquaculture, also known as aquafarming, is the farming of aquatic organisms such as fish, crustaceans, molluscs and aquatic plants. Aquaculture involves cultivating freshwater and saltwater populations under controlled conditions, and can be contrasted with commercial fishing, which is the...

, but can also occur in natural populations.

Fin rot can be the result of a bacteria

Bacteria

Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

l infection (Pseudomonas fluorescens

Pseudomonas fluorescens

Pseudomonas fluorescens is a common Gram-negative, rod-shaped bacterium. It belongs to the Pseudomonas genus; 16S rRNA analysis has placed P. fluorescens in the P. fluorescens group within the genus, to which it lends its name....

, which causes a ragged rotting of the fin), or as a fungal

Fungus

A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...

 infection (which rots the fin more evenly and is more likely to produce a white 'edge'). Sometimes, both types of infection are seen together. Infection is commonly brought on by bad water conditions, injury, poor diet, or as a secondary infection in a fish which is already stressed by other disease.

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.

Fin rot is very common in Betta

Betta

Betta is a large genus of small, often colorful, freshwater ray-finned fishes in the gourami family . The type species is B. picta, the spotted betta.By far the best known Betta species, however, is B...

s due to poor water conditions in pet stores.

Symptoms:

• Fin edges turn black / brown
• Fins fray
• Base of fins inflamed
• Entire fin may rot away or fall off in large chunks

Ways to treat:

• Change the water
• Treat with herbal remedies like Melafix
• Use common salt
• Find out the pH and correct it

Use medication specifically for fin rot:

• Maracyn TC (for positive bacterial infections)
• Maracyn 2 (for negative bacterial infections)
• Melafix (as a preventative)

Prevention:

• Make sure the water is good quality
• Feed fresh food in small portions
• Maintain constant water temperature

External links

• Fin rot: Symptoms and Treatment at AquaDaily
• Diagnosis, prevention and treatment information at the Aquarium Wiki
• http://www.practicalfishkeeping.co.uk/pfk/pages/show_article.php?article_id=263 Practical Fishkeeping Magazine article on fin rot.