Gill Trichodinids of Scallops


Category 4 (Negligible Regulatory Significance in Canada)

Common, generally accepted names of the organism or disease agent

Gill trichodinids.

Scientific name or taxonomic affiliation

  1. Unidentified trichodinid ciliate.
  2. Trichodina pectenis, Trichodina sp.

Geographic distribution

  1. On sea scallops from Atlantic Canada but may have a wider distribution, including a wide variety of other marine bivalves such as oysters, clams and cockles.
  2. Gulf of Peter the Great (Sea of Japan).
  3. Tongoy Bay, Chile.

Host species

  1. Placopecten magellanicus.
  2. Patinopecten yessoensis.
  3. Argopecten purpuratus.

Impact on the host

  1. All observations to date are based on histology. Counts of up to 71 trichodinids per tissue-section show no evidence of host response (prevalence 0-90%, 1-71 per section).
  2. Prevalence varied from 20-100% with no directly associated pathology. They may play a role as secondary parasites since they often appear in very large numbers on the body of weakened scallops.
  3. Observed adjacent to gill tissue with no evidence of tissue damage nor a host response. However, prevalence was significantly higher in cultured scallops (56%) than in wild scallops (5%) from the same area (Lohrmann et al. 2002).

Diagnostic techniques

Histology: Disc-shaped protista characterised by a circlet of eosinophilic denticles, ciliary fringes, and a horse-shoe shaped nucleus.

Methods of control

No known methods of prevention or control. Managers of areas currently free of these ciliates may wish to prevent their introduction.


Ball, M.C. and S.E. McGladdery. 2001. Scallop parasites, pests and diseases: implications for aquaculture development in Canada. Bulletin of the Aquaculture Association of Canada 101-3: 13-18.

Kurochkin, Y.V., E.M. Tsimbalyuk and A.V. Rybakov. 1986. Parazitî i bolyezni. (Parasites and diseases.). In: P.A. Motavkin (ed.). Primorskii grebeshok. (The Yezo scallop or Japanese common scallop Mizuhopecten yessoensis (Jay).). Institute of Marine Biology, Far East Science Centre, Academy of the USSR, Vladivostok, p. 174­182. (In Russian).

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.

Lohrmann, K.B., A.R. Brand and S.W. Feist. 2002. Comparison of the parasites and pathogens present in a cultivated and in a wild population of scallops (Argopecten purpuratus Lamarck, 1819) in Tongoy Bay, Chile. Journal of Shellfish Research 21: 557-561.

McGladdery, S.E., R.E. Drinnan and M.F. Stephenson. 1993. A Manual of the parasites, pests and diseases of Canadian Atlantic bivalves. Canadian Technical Report of Fisheries and Aquatic Sciences No. 1931, p. 105-106.

McGladdery, S.E. and M.F. Stephenson (unpublished data). Parasites and diseases of wild and suspension-grown sea scallop Placopecten magellanicus from Newfoundland. Atlantic Canadian Association of Parasitologists, Mont-Joli, Quebec, October 1991.

Citation Information

Bower, S.M., McGladdery, S.E. (2004): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Gill Trichodinids of Scallops.

Date last revised: May 2004
Comments to Susan Bower

Date modified: