Ancistrum mytili Gill Ciliate of Mussels


Category 4 (Negligible Regulatory Significance in Canada)

Common, generally accepted names of the organism or disease agent

Gill ciliates of mussels

Scientific name or taxonomic affiliation

Ancistrum mytili

Geographic distribution

Appears to be ubiquitous with reports from mussels throughout their geographic range.

Host species

Mytilus edulis, Mytilus spp.

Impact on the host

Large numbers elicit no obvious host-response and attachment to the gill epithelia appears to be superficial. In the Thermaikos Gulf (north Aegean Sea, Greece), infection caused no visible lesions in histological sections of the gills and no significant difference in the condition index (Rayyan et al., 2006). In the eastern Maritime Provinces of Canada, A. mytili occurs in about 90 to 100% of the mussels. From 0.1% to 5.0% of these A. mytili are infected with a Chlamydia or Rickettsia hyperparasite (Moret et al. 1999b). It has been speculated that excessively heavy infections may have a secondary pathogenic effect under adverse growing conditions, but there has been no evidence of this to date. In one location (Ria de Aveiro, Portugal), this ciliate was reported to be within the gonad of female mussels where it apparently obtained nutrients from the oocytes (Teia dos Santos and Coimbra 1995).

Diagnostic techniques

Smears: Check smears of the gills under a microscope for free-swimming ciliates measuring 30-60 µm in length.

Histology: Ciliates lie on or in-between the gill lamellae, have a large densely basophilic macronucleus and a smaller posteriorly located micronucleus. The body is pyriform in shape with a pointed anterior end. Attachment is superficial and there is no evidence of tissue penetration. Rickettsial-like hyperparasites may also be present, appearing as densely basophilic, lobular, inclusion bodies within the cytoplasm of the ciliate. Similar, but as yet unidentified, ciliates also occur in the intestine.

Methods of control

Prevention and control impractical. These ciliates are ubiquitous.


Bower, S.M. 1992. Diseases and parasites in mussels. In: E. Gosling (ed.) The Mussel Mytilus: Ecology, Physiology, Genetics and Culture. Elsevier Press Amsterdam, p. 543-563.

Fenchel, T. 1965. Ciliates from Scandinavian molluscs. Ophelia 1: 113-120.

McGladdery, S.E., R.E. Drinnan and M.F. Stephenson. 1993. A manual of parasites, pests and diseases of Canadian Atlantic bivalves. Canadian Technical Report of Fisheries and Aquatic Sciences 1931, p. 68-69.

Moret, K., C. Couturier, G.J. Parsons and K. Williams. 1999a. Monitoring shellfish health in Newfoundland: a preventative approach. Journal of Shellfish Research 18: 297-298. (Abstract).

Moret, K., K. Williams, C. Couturier and J. Parsons. 1999b. Newfoundland cultured mussel (Mytilus edulis) industry 1997 health survey. Bulletin of the Aquaculture Association of Canada 99-3: 35-37.

Rayyan, A., P. Damianidis, C. Antoniadou and C.C. Chintiroglou. 2006. Protozoan parasites in cultured mussels Mytilus galloprovincialis in the Thermaikos Gulf (north Aegean Sea, Greece). Diseases of Aquatic Organisms 70: 251-254.

Teia dos Santos, A.M. and J. Coimbra. 1995. Growth and production of raft-cultured Mytilus edulis L., in Ria de Aveiro: gonad symbiotic infestations. Aquaculture 132: 195-211.

Citation Information

Bower, S.M. (2007): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Ancistrum mytili Gill Ciliate of Mussels

Date last revised: August 2007
Comments to Susan Bower

Date modified: