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What is Fin Rot (or Tail or Gill Rot)?

Finrot is a common bacterial disease of fish kept in low quality water conditions.

It is caused by gram negative bacteria like Aeromonas, Pseudomonas, or Vibrio which eats the delicate membranes of fish. Usually the area of the damaged fin becomes opaque and white then is eaten away by the bacteria. Often fungus develops giving the wound a fluffy appearance. It is easily treated and the fin will grow back if not too badly damaged.

  • Tail Rot is named thus as it it appears initially in the tail (caudal) region
  • Gill Rot is named thus as it it appears initially in the Gill region as white patches.
  • If not treated the fish will usually die.


This serious bacteria can causes fin/tail/gill rot as well. If the usual bacterial treatments prove not to work then your animal may be infected with Mycobacteriosis.


  • Bad water - regular changing of the tank water and lowering of wasted fish food will prevent the levels of bacteria from climbing.
  • Fin damage due to overcrowding, handling, other fish.


  • Regular water changes can often cure this if it's not too advanced.
  • Adding a level of salt to the water is a good mild treatment if the species of fish can tolerant it.
  • Antibiotics (not available in Europe over the counter) are an option for advanced cases. Chloramphenical, Oxytetracycline, and Tetracycline for example.
  • Fitting a UV device to the tank will help keep the levels of bacteria down.

Commercial treatments

King British


  • No.8 - Anti Fungus and Fin Rot
  • No.10 - Methylene Blue
  • Catalogue


Pets at Home

  • Disease Treatment (contains Protargol 0.151% w/w (Silver proteinate) [2]

API (Aquarium Pharmaceuticals)

Tetra UK

Tetra USA

  • Lifeguard™ All-in-One - Kills bacteria, fungus and parasites.

Jungle Labs (USA)

  • Lifeguard - All-in-One - Kills bacteria, fungus and parasites (contains HaloShield (1-chloro-2,2,5,5-tetramethyl-4-imidazolidinone))
  • Anti-Bacteria Medicated Fish Food - for bacterial Infections (Mouth rot)
  • Binox (Crystal) Broad range anti-bacterial and Fungus treatment contains Nitrofurazone <9%. See MSDS)


  • TRICIDE-Neo™ - Antibacterial Dip - a concentrate of NeoMycin antibiotic [3]


  1. 1.0 1.1 1.2 1.3 Veterinary Medicines Marketed under the Small Animal Exemption Scheme, VMD
  2. 2.0 2.1 Chemical information on the product
  3. Tricide Neo tris-EDTA Solution Against Bacterial Infections


  • Fitting a UV device to the tank will help to keep the levels of bacteria down.
  • Setting up a tank with a natural soil-based substrate will suppress the levels of this bacteria down. See Walstad.