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This information is provided by Provet for educational purposes only.

You should seek the advice of your veterinarian if your pet is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your pet.

Fin rot is a common problem in aquarium and farmed fish - but what causes it ?

Most fish-keepers have seen fish that lose part or all of a fin. Usually one or more fin becomes frayed and sections of it erode off and disappear. This is popularly called "fin rot" and there are several causes including :

  • Trauma
  • Poor water quality. Ensure the following levels :
    • Oxygen  >5.5 mg/l
    • Ammonia < 0.01 mg/l
    • Nitrate < 40mg/l
    • Nitrite <0.125 mg/l
    • Avoid chemical contamination
    • Some fish are pH sensitive
  • Bacterial infections - Aeromonas or Pseudomonas
  • Protozoal infection
  • Ectoparasites

Various treatments can be used to treat fin rot. For bacterial infections :

a)  Chloramine T - is effective against bacteria and ectoparasites. It is administered in a bath at the following dose rates (ppm = parts per million parts of water) , using lower dose rates in soft water with a low pH :

Water pH Soft Water (low pH) Hard Water
6.0 2.5 ppm 7.0 ppm
6.5 5 ppm 10 ppm
7.0 10 ppm 15 ppm
7.5 18 ppm 18 ppm
8.0 20 ppm 20 ppm

b) Benzalkonium chloride - administered in a bath - using lower dose rates in soft water with a low pH :

  • 10 ppm - duration of treatment 5-10 minutes
  • 5 ppm - duration of treatment 30 minutes
  • 2 ppm - duration of treatment 1 hour
  • 1 ppm - duration of treatment several hours

c) Various specific antibiotics have been used including :

  • Oxytetracycline  - 75 mg/kg body weight with food
  • Oxolinic acid - 10-30mg/kg body weight with food
  • Potentiated sulphonamides - sulfadiazine and trimethoprim 30mg/kg body weight with food


Updated October 2013