List of Koi Diseases

An image of a goshiki koi fish afflicted with disease.


  • Hole Disease, Ulcer Disease, Flesh-eating Bacteria (Aeromonas sp.)
  • Bacterial Dropsy, Pine Cone Disease, Bloat (Aeromonas sp. & Pseudomonas sp.)
  • Fin Rot (Aeromonas sp. & Pseudomonas sp.)
  • Columnaris  (Flavobacterium columnare)
  • Fish Tuberculosis (Mycobacterium sp.)


  • Carp Pox, Cyprinid Herpesvirus 1, CyHV-1
  • Koi Herpes Virus, Cyprinid Herpesvirus 3, CyHV-3, KHV
  • Carp Edema Virus Disease, Koi Sleepy Disease, CEVD, CEV, KSD


  • Fish Lice (Argulus sp.)
  • Anchor Worm (Lernaea sp.)
  • Ich, White Spot Disease (Ichthyophthirius multifiliis)
  • Gill Fluke (Dactylogyrus sp. & Gyrodactylosis sp.)
  • Cotton Wool, Water Mold (Saprolegnia sp.)
  • Hex, Hole-in-the-head Disease, HITH (Hexamita sp.)
  • Red Sore Disease (Epistylis sp.)
  • Costia, Costiasis (Ichthyobodo sp.)
  • Trichodina (Trichodina sp.)
  • Chilodonella (Chilodonella sp.)

Other Diseases / Ailments

  • pH Shock, Temperature Shock (Sudden change in water parameters such as pH and temperature)
  • Ammonia/Nitrite/Nitrate Poisoning, Ammonia Burn (Dangerous levels of waste and toxins built up in environment)
  • Chlorine/Chloramine Poisoning  (Undechlorinated tap water, massive water change without dechlorination)
  • Hydrogen Sulfide (Deadly byproduct of anaerobic bacteria living in deep low-oxygen substrate)
  • Non-bacterial Bloat (Varies, may be as simple as poor diet induced constipation)
  • Vitamin B Deficiency (More commonly affects predatory fish fed on thiaminase rich koi and goldfish which breaks down usable vitamin B)
  • Fatty Liver Disease (Diet excessive in fats)
  • Ovarian Cancer (Can be genetic as well as excessive use of carcinogenic medications)
  • Genetic Deformities (Curled gills, bent fins, bent tail)