From Fish
Tail of chum salmon fry infected with Trichodina spp
Trichodina parasitized the fin of chum salmon.
SEM of Trichodina on the gill.

Trichodina spp (Taxonomy:Ciliophora, Oligohymenophorea) are a ciliated, protozoan parasite of skin, gills and skin of many freshwater and marine fishes.

Life cycle

The parasite body is semipherical and several tens to several hundreds mm in diameter (Fig. 3). Trichodina attaches on the fish host by the denticles at the central part of the adhesive disc and the marginal cilium. It feeds on bacteria and detritus particles from the fish surface, and proliferates by binary fission[1]. Well-known species are Trichodina reticulate from common carp and goldfish, T. truttae from salmonids, etc.

Clinical signs

Infected fish usually exhibits no external abnormality. Wheel-like parasites are observed under a stereomicroscope. Trichodina is the opportunistic parasite because it proliferates when host’s immune system is deteriorated. In heavily infected fish, the skin is injured and mucus secretions are evident. Mass mortalities (cumulative loss of 56 %) occurred in juvenile chum salmon Oncorhynchus keta infested with T. truttae in a transmission experiment[2]. Disease outbreaks caused by T. murmanica were reported in Atlantic cod Gadus morhua. Diseased cod showed epidermal and fin erosion, and tail necrosis.

Since this parasite is not infectious to human, it is harmless in food hygiene.


Under the microscope, these organisms look like tiny, rotating, ciliated discs. Trichodina do not feed on fish tissues, but rather use their host as a means of transport. In high concentration, however, they can be extremely irritating to the host organism, as the sucking disc they use for attachment can cause damage to delicate gill filaments or epithelium of the fish[3].


  1. Lom, J and I. Dykova (1992) Protozoan Parasites of Fishes, Developments in Aquaculture and Fisheries Science, 26, Elsevier, pp. 315.
  2. Urawa, S. (1992) Trichodina truttae Mueller, 1937 (Ciliophora: Peritrichida) on juvenile chum salmon (Oncorhynchus keta): pathogenicity and host-parasite interactions. Fish Pathol 27:29-37
  3. Khan, R. A. (2004) Disease outbreaks and mass mortality in cultured Atlantic cod, Gadus morhua L., associated with Trichodina murmanica (Ciliophora). J Fish Dis 27:181-184