Kidney Coccidia of Scallops


Category 2 (In Canada and of Regional Concern)

Common, generally accepted names of the organism or disease agent

Scallop kidney coccidia.

Scientific name or taxonomic affiliation

  1. Pseudoklossia pectinis, this species was probably assigned to the incorrect genus because Léger and Duboscq (1917) described and illustrated gamonts in syzygy, a key feature of adeleorin coccidians that is not present in coccidia of the family Aggregatidae Labbé where species in the genus Pseudoklossia currently occur.
  2. Unidentified species of coccidia. In light of the discussion presented by Desser and Bower (1997) concerning taxonomic affiliations of coccidia of molluscs, preliminary assignment to the genus Pseudoklossia must be reconsidered when developmental stages of this parasite have been described.

Other species of coccidia have been described from the kidneys of oysters, mussels, clams and abalone from various locations around the world.

Geographic distribution

  1. Roscoff, France.
  2. Eastern Canada and eastern U.S.

Host species

  1. Pecten maximus.
  2. Argopecten irradians.

Impact on the host

Infected kidney epithelial cell become hypertrophied and the kidney tubules fill with coccidia. Heavy infections may cause kidney damage and have been observed to spread to other tissues (mantle, digestive gland, intestine, gill and gonad). However, little or no apparent host response was elicited against the coccidian regardless of the tissue invaded. Associated mortalities appear restricted to artificial growing conditions.

Diagnostic techniques

Squash Preparations: Preliminary diagnosis can be made on the presence of large mature macrogamonts in squashes of kidney tissues.

Histology: Various stages of the coccidia can be observed in the cytoplasm of kidney epithelia and within the kidney lumens. In heavy infections, various stages may occur systemically in the connective tissue and epithelia of organs adjacent to the kidney.

Methods of control

No known methods of prevention or control.


Cawthorn, R.J., R.J. MacMillan and S.E. McGladdery. 1992. Epidemic of Pseudoklossia sp. (Apicomplexa) in bay scallops Argopecten irradians maintained in a warm water recirculating facility. (Abstract) 31st. Annual meeting, Canadian Society Zoologists, May 13-15, Antigonish, N.S. Bulletin of the Canadian Society of Zoologists 23(2): 37-38

Desser, S.S. and S.M. Bower. 1997. Margolisiella kabatai gen. et sp. n. (Apicomplexa: Eimeriidae), a parasite of native littleneck clams, Protothaca staminea, from British Columbia, Canada, with a taxonomic revision of the coccidian parasites of bivalves (Mollusca: Bivalvia). Folia Parasitologica 44: 241-247.

Getchell, R.G. 1991. Diseases and parasites of scallops. In: S.E. Shumway (ed.). Scallops: Biology, Ecology and Aquaculture. Developments in Aquaculture and Fisheries Science No. 21. Elsevier Press, p. 471-494.

Karlsson, J.D. 1991. Parasites of the bay scallop Argopected irradians (Lamarck, 1819). In: S.E. Shumway and P.A. Sandifer (eds.). An International Compendium of Scallop Biology and Culture. The World Aquaculture Society. Baton Rouge, p. 180-190.

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. 548.

Léger, L. and O. Duboscq. 1917. Pseudoklossia pectinis n. sp. et l'origine des adéleidées. Archives de Zoologie Expérimentale et Générale 56: 88-95.

McGladdery, S. 1990. Shellfish parasites and diseases on the east coast of Canada. Bulletin of the Aquaculture Association of Canada 90: 14­18.

Whyte, S.K., R.J. Cawthorn and S.E. McGladdery. 1994. Co-infection of bay scallops Argopecten irradians with Perkinsus karlssoni (Apicomplexa, Perkinsea) and an unidentified coccidian parasite. Diseases of Aquatic Organisms 18: 53-62.

Citation Information

Bower, S.M. (1998): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Kidney Coccidia of Scallops.

Date last revised: July 1998
Comments to Susan Bower

Date modified: