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What is it?

Trichodina is caused by protozoan ciliate parasites of genus Trichodina. They are small, about 50 µm in diameter.

They live in the mulm of the substrate and filter systems waiting for a passing aquatic animal to come near enough for them to latch onto the surface of the animal.


They reproduce by binary fission (each cell splits into two) and they have a single host and


Trichodinids are typically found on the gills, skin and fins of fishes, though some species parasitise the urogenital system. A range of invertebrates are also host to trichodinid infections, including the surfaces of copepods and the mantle cavity of molluscs and snails. Transmission occurs by direct contact of infected and uninfected hosts, and also by active swimming of trichodinids from one host to another.

They feed off the bacteria on the fish surface and cause the fish irritation.


Poor water quality which usually means high bacterial counts provides a source of food for this parasite and so leads to high numbers of the parasite.


Fish flicks and rubs against surfaces causing surface damage of the skin. The method of attachment by the parasite also damages the skin surface which can lead to bacterial and ulcer infections.

In heavy infestations the fish will be lethargic, they may isolate themselves, stop feeding and lay on the bottom with clamped fins. It rarely kills. But does cause extreme stress which can make them susceptible to further bacterial and fungi infections.

  • Heavy infections of Trichodina can cause a greyish, white film over the body of the fish. Using a microscope of 200X will show individual parasites.


  • Treat as if it was Ich.
  • Potassium permanganate at 1.5ppm seems to be very effective.[1]
  • Malachite green with Formalin
  • Salt at 3% for emergency short term treatment. Low levels are often no use as this parasite is becoming resistant to salt.

Commercial treatments

King British



Pets at Home

  • None

API (Aquarium Pharmaceuticals)

Tetra UK

Tetra USA

Jungle Labs (USA)


  • Proform C - Malachite Formalin mix for parasite control in ornamental systems and ponds (contains Malachite green and formalin)

Special notes

  • Believed to be common in imported species like the Golden Barb