Bacterial Abscess Lesions of Scallops


Category 2 (In Canada and of Regional Concern)

Common, generally accepted names of the organism or disease agent

Bacterial abscess disease (BAD), Bacterial abscess lesions, Brown spot.

Scientific name or taxonomic affiliation

Gram-positive bacterium.

Geographic distribution

Northeastern U.S. and Atlantic Canada.

Host species

Placopecten magellanicus.

Impact on the host

Disruption of adductor muscle fibres may result in poor swimming and closing ability and eventually results in death. Only recorded from wild giant sea scallop populations (5-10% prevalence).

Diagnostic techniques

Gross Observations: Systemic bacterial infection resulting in visible brown spots (abscesses up to 3 mm in diameter) on the adductor muscle which, as a result, is unmarketable.

Histology: Focal haemocyte infiltration throughout the tissues associated with aggregations of Gram-positive bacteria. In the adductor muscle, muscle fibres show disruption associated with haemocyte infiltration, necrosis and abscessing.

Methods of control

No known methods of prevention or control since all reported cases are from wild populations. Possible tissue trauma initiation merits close monitoring in the aquaculture situation, where net-held scallops can be damaged by shell overlap (biting).


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.

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

Sherburne, S.W. and L.L. Bean. 1986. A synopsis of the most serious diseases occurring in Maine shellfish. American Fisheries Society, Fish Health Section Newsletter 14: 5.

Citation Information

Bower, S.M., McGladdery, S.E., Price, I.M. (1994): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Bacterial Abscess Lesions of Scallops

Date last revised: Fall 1994
Comments to Susan Bower

Date modified: