Also known as the “scrubbing bubbles,” trichodina is caused by freshwater parasites commonly found on koi and goldfish. Although there are many species, they all have a similar appearance and behavior. They are circular in shape and have multiple teeth that ratchet around, feeding on skin and mucus.
Here you can watch them in action:
And closer up:
Trichodina is a relatively mild parasitic disease and usually made worse by poor water quality. Mature fish will show signs of flashing and with severe infestations may be anorexic and/or poor body condition, but rarely die. Younger fish are more susceptible to experiencing mortality with heavy infestations.
Be sure to have a confirmed diagnosis of Trichodina from your veterinarian before proceeding with treatment. There are many other pathogens, such as flukes or costia, that can cause identical clinical signs.
Treatment for trichodinosis is relatively easy and straight forward. They do not have an encysted life stage, like white spot, and most will recover from mild infestations with improvement in water quality.