Branchiobdellida Annelid Parasitism of Crayfish


Category 4 (Negligible Regulatory Significance in Canada)

Common, generally accepted names of the organism or disease agent

Branchiobdellida annelid parasitism, Leech-like infection of gills.

Scientific name or taxonomic affiliation

Branchiobdella hexodonta, Branchiobdella parasitica, Cambarincola chirocephala, Pterodrilus distichus and possibly Branchiobdella astaci and other species of this order (Branchiobdellida) of clitellate annelids (intermediate between oligochaetes and leeches).

Geographic distribution

North America, Europe, Eastern Asia and Japan.

Host species

Ubiquitous in the Northern Hemisphere, but some species seems to have a limited geographical distribution. Although some species are adapted to microniches on their hosts, no branchiobdellid appears to be host specific. One crayfish may harbor several branchiobdellid species (Holt 1975).

Impact on the host

Although some species such as Branchiobdella parasitica, Cambarincola chirocephala, and Pterodrilus distichus are thought to be commensals or at most facultatively parasitic, other species, such as B. hexodonta, feeds on host tissue. Parasitic species occurring on the gills cause melanization of the gill filaments. Constant wounding by the feeding branchiobdellid may provide a route of entry for other pathogens but the intensity of branchiobdellid infection is usually too low to account for direct mortalities.

Diagnostic techniques

Gross Observations: Leech-like branchiobdellid (1-12 mm long) attached to surface of crayfish by suckers (modified anterior and posterior segments) with associated damage and melanization of gills when found in the branchial chamber.

Methods of control

No known method of control. Infected crayfish should not be transplanted to other areas.


Alderman, D.J. and J.L. Polglase. 1988. Pathogens, parasites and commensals. In: D.M. Holdich and R.S. Lowery (eds.). Freshwater Crayfish ­ Biology, Management and Exploitation. Timber Press, OR., p. 200-203.

Bishop, J.E. 1968. An ecological study of the branchiobdellid commensals (Annelida-Branchiobdellidae) of some mid-western Ontario crayfish. Canadian Journal of Zoology 46: 835-843.

Holt, P.C. 1975. The branchyobdellid (Annelida: Clitellata) associates of Astacoidean crawfish. In: Avault, J.W. (ed.), Freshwater Crayfish, Papers from the Second International Symposium on Freshwater Crayfish, Baton Rouge, Louisiana, U.S.A. 1974. Louisana State University, Baton Rouge, pp. 337-346.

Pennak, R.W. 1953. Fresh-water Invertebrates of the United States. The Ronald Press Company, New York. p. 284-300.

Pennak, R.W. 1989. Fresh-water invertebrates of the United States:Protozoa to Mollusca. 3rd edn. John Wiley & Sons, Inc., New York. p. 307-312

Citation Information

Bower, S.M., McGladdery, S.E. (2002): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Branchiobdellida Annelid Parasitism of Crayfish.

Date last revised: April 2002
Comments to Susan Bower

Date modified: