Gill Trichodinids of Oysters


Category 4 (Negligible Regulatory Significance in Canada)

Common, generally accepted names of the organism or disease agent

Gill trichodina.

Scientific name or taxonomic affiliation

Trichodina spp., other unidentified trichodinid ciliates.

Geographic distribution

Reported from various species of oysters from Europe, eastern United States and the Pacific rim.

Host species

Crassostrea gigas, Crassostrea angulata as well as other oysters and other marine bivalves including clams, cockles and scallops.

Impact on the host

Most infections are innocuous with a low intensity of these ciliates attached to, or located near the mantle, labial palps, or gill surface. Heavy infections in Crassostrea angulata were associated with erosion of the gill filaments, emaciation, and appreciable losses in Seudre, France. But, the Trichodina sp. may have been a secondary invader of Portuguese oysters that were suffering from virus-caused gill disease.

Diagnostic techniques

Wet Mounts: Disc-shaped ciliates, that swim through the sea water like flying saucers or adhere to the glass surface like a suction cup, can be observed in scrapings of the mantle cavity lining (100x). For specific identification the specimens must be properly stained (using silver impregnation techniques).

Histology: Disc-shaped protozoa (30 to 50 µm in diameter) characterized by a circlet of eosinophilic denticles, ciliary fringes, and a horse-shoe shaped nucleus.

Figure 1. Trichodina sp. near the mantle surface of Crassostrea gigas with no evidence of pathology in the adjacent tissue including the epithelium.

Fig. 1B is a higher magnification of part of Fig. 1A. Haematoxylin and eosin stain.

Methods of control

No known methods of prevention or control.


Lauckner, G. 1983. Diseases of Mollusca: Bivalvia. In: O. Kinne (ed.) Diseases of Marine Animals. Volume II: Introduction, Bivalvia to Scaphopoda. Biologische Anstalt Helgoland, Hamburg, p. 593-598.

Citation Information

Bower, S.M., McGladdery, S.E., Price, I.M. (1994): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Gill Trichodinids of Oysters.

Date last revised: Fall 1994
Comments to Susan Bower

Date modified: