Chitinolytic Fungal Disease (Black Mat Syndrome) of Crabs


Category 2 (In Canada and of Regional Concern)

Common, generally accepted names of the organism or disease agent

Chitinolytic fungus disease, Black mat syndrome, or Trichomariasis in Tanner crab.

Scientific name or taxonomic affiliation

Trichomaris invadens.

Geographic distribution

Alaska, USA and probably also British Columbia, Canada.

Host species

Chionoecetes bairdi, rarely on Chionoecetes opilio and Chionoecetes tanneri.

Impact on the host

Hyphae penetrate the exoskeleton and invade many internal tissues resulting in a significant increase in the percentage of eosinophilic granulocytes in circulating haemolymph. Moderate infection probably prevents moulting, invasion of the eyes probably causes blindness, and is a potentially lethal disease.

Diagnostic techniques

Gross Observations: External manifestation begins as small discrete black spots on the exoskeleton that enlarge and coalesce until the entire carapace and appendage surfaces become a black tarry-looking mass.

Squash Preparations: Microscopic examination of unstained squash preparations of epidermis and subepidermal tissues of crabs with the syndrome should reveal the nonpigmented hyphae.

Histology: Internal hyphae usually elicit no host response. Peritheca and the hyphae on the surface of the exoskeleton and hyphae within adjacent epidermis and subepidermal layers are evident in tissue stained with Grocott's methanimine silver.

Methods of control

No known methods of prevention or control.


Brock, J.A. and D.V. Lightner. 1990. Diseases of Crustacea. Diseases caused by microorganisms. In: O. Kinne (ed.). Diseases of Marine Animals. Volume III: Introduction, Cephalopoda, Annelida, Crustacea, Chaetognatha, Echinodermata, Urochordata. Biologische Anstalt Helgoland, Hamburg, p. 345-348.

Sparks, A.K. 1982. Observations on the istopathology and probable progression of the disease caused by Trichomaris invadens, an invasive ascomycete, in the Tanner crab, Chionoecetes bairdi. Journal of Invertebrate Pathology 40: 242-254.

Sparks, A.K. 1985. Synopsis of Invertebrate Pathology Exclusive of Insects. Elsevier Science Publishing Co., Amsterdam. p. 230-234.

Citation Information

Bower, S.M., McGladdery, S.E., Price, I.M. (1994): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Chitinolytic Fungal Disease (Black Mat Syndrome) of Crabs.

Date last revised: Fall 1994
Comments to Susan Bower

Date modified: