Fin Rot

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Technically referred to as skin ulcers, fin rot is limited to the fins with skin ulcers refering to the body.[1] Fin rot, also known as tail rot, is a disease of marine and freshwater fish where a microbial infection causes a progressive degeneration of the fins. Starting as discoloration and erosion of the outer margins of the fin leaving a tattered appearance, the infection slowly progresses to expose the fin rays. The rays and skin are slowly eroded eventually leading to total fin loss. Skin ulcers may be associated with fin rot.


Complex microbial assemblage are associated with effected skin, often dominated by water mould (oomycetes)[1] and multiple genera of bacteria[2], most notablyPseudomonas[2] but also inclunding Vibrio, Aeromonas[2] and Edwardsiella[3]. Several predisposing factors either on there own or combined may lead to the onset of infection:

  • Poor water quality
  • Stress
  • Injury
  • Poor nutrition
  • Disease
  • Secondary infection due to a parasitic infection


  • Fraying and splitting, starting from the outer extremities of the fin.
  • Redness and opaque margins.

Advanced cases may result in the total loss of fins and death.

Similar Symptoms


Any underlying causes must first be treated or corrected. If symptoms persist or progress then treatment with an antibiotic in a quarantine tank may be necessary.




  1. 1.0 1.1 ( Noga, E., Review Article: Skin Ulcers in Fish: Pfiesteria and Other Etiologies, Toxicol Pathol, 28(6), (2000), 807-823.
  2. 2.0 2.1 2.2 ( Mahoney, J., Midlige, F., Deuel, D., A Fin Rot Disease of Marine and Euryhaline Fishes in the New York Bight, Transactions of the American Fisheries Society, 102(1), (1973), 596-605.
  3. (Bassleer 2004): Bassleer, G., Disease in Marine Aquarium Fish: Causes - Development - Symptoms - Treatment, Bassleer Biofish: Belgium, 2004.