Paramoeba perniciosa (Grey Crab Disease)


Category 1 (Not Reported in Canada)

Common, generally accepted names of the organism or disease agent

Grey crab disease, Paramoebiasis.

Scientific name or taxonomic affiliation

Paramoeba perniciosa.

Geographic distribution

East coast of the United States from Connecticut to Florida including high salinity areas of Chincoteague Bay and Chesapeake Bay.

Host species

Callinectes sapidus; also reported from Cancer irroratus, Carcinus maenas and Homarus americanus.

Impact on the host

Parasitic amoebae progressively invade the connective tissues along the midgut, the antennal gland, Y organ and the haemal spaces in the gills. Eventually the infection becomes systemic. Pathological changes caused by large numbers of amoeba include: tissue displacement, probable lysis of some types of tissue including haemocytes, and significant decreases in protein, haemocyanin and glucose. Epizootics involving mortalities as high as 17% of the blue crab population have been reported from Chincoteague Bay in early summer and mortalities in shedding tanks (for production of newly moulted softshell crab) have been estimated at 20-30%.

Diagnostic techniques

Gross Observations: Greyish discolouration of the ventral exoskeleton, general sluggishness, reduced or absence of clotting of the haemolymph, and poor survival subsequent to handling or holding in tanks.

Squash Preparations: Before the amoebae appear in the circulation, they may be observed by phase contrast in subepithelial connective tissue. In advanced cases, amoeba can be observed in the blood either live or fixed in 5% formalin seawater and stained with dilute methylene blue. Haemocytes are few or absent.

Smears: Fix in Bouin's, Davidson's, Hollande's, or 10% formalin solutions and stained with iron haematoxylin or Giemsa's stain. Amoeba (round to elongate, 3-35 µm) contain a well-defined nucleus with a large central endosome plus a characteristic, morphologically different secondary nucleus-like body in the cytoplasm.

Methods of control

No known methods of prevention or control.


Couch, J.A. 1983. Diseases caused by protozoa. In: A.J. Provenzano Jr. (ed.). The Biology of Crustacea. Volume 6, Pathobiology. Academic Press, New York, p. 79-111.

Johnson, P.T. 1977. Paramoebiasis in the blue crab, Callinectes sapidus. Journal of Invertebrate Pathology 29: 308-320.

Johnson, P.T. 1988. Paramoebiasis of blue crabs. In: C.J. Sindermann and D.V. Lightner (eds.). Disease Diagnosis and Control in North American Marine Aquaculture. Developments in Aquaculture and Fisheries Science 17. Elsevier, Amsterdam, p. 204-207.

Newman, M.W. and G.E. Ward. 1973. An epizootic of blue crab, Callinectes sapidus, caused by Paramoeba perniciosa. Journal of Invertebrate Pathology 22: 329-334.

Pauley, G.B., M.W. Newman and E. Gould. 1975. Serum changes in the blue crab, Callinectes sapidus, associated with Paramoeba perniciosa, the causative agent of grey crab disease. Marine Fisheries Review 37: 34-38. (MFR Paper 1145).

Sawyer, T.K. and S.A. MacLean. 1978. Some protozoan diseases of decapod crustaceans. Marine Fisheries Review 40: 32-35. (MFR Paper 1342).

Sprague, V., R.L. Beckett and T.K. Sawyer. 1969. A new species of Paramoeba (Amoebida, Paramoebidae) parasitic in the crab Callinectes sapidus. Journal of Invertebrate Pathology 14: 167-174.

Citation Information

Bower, S.M., McGladdery, S.E., Price, I.M. (1994): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Paramoeba perniciosa (Grey Crab Disease).

Date last revised: Fall 1994
Comments to Susan Bower

Date modified: