Sirolpidium zoophthorum (Larval Mycosis) of Clams


Category 4 (Negligible Regulatory Significance in Canada)

Common, generally accepted names of the organism or disease agent

Larval mycosis, Sirolpidium mycosis.

Scientific name or taxonomic affiliation

Sirolpidium zoophthorum.

Geographic distribution

Hatchery-related mortalities recorded from along eastern U.S. Also occurs in wild populations, but not yet associated with observed mortalities.

Host species

Mercenaria mercenaria (also reported from Crassostrea virginica).

Impact on the host

Affects larvae ranging in stage from early veliger to post-metamorphic juveniles up to 400 µm in diameter. Fungus spreads throughout the soft-tissues causing them to disintegrate. The sporangia produce tubes which protrude outside the shell and release motile zoospores. In heavily infected larval cultures over 90% of larvae can be killed within two days.

Diagnostic techniques

Wet Mounts: Larvae contain looped, sparsely branched mycelia, with constrictions at intervals between segments which may be swollen and frequently lobed. The fungus can be detected in living larvae placed in a neutral red, seawater solution.

Methods of control

No known treatment. Disease probably related to poor husbandry. Destroy batches containing infected individuals in an approved manner. Disinfect all containers and equipment.


Davis, H.C., V.L. Loosanoff, W.H. Weston and C. Martin. 1954. A fungus disease in clam and oyster larvae. Science 120: 36-38.

Vishniac, H.S. 1955. The morphology and nutrition of a new species of Sirolpidium. Mycologia 47: 633-645.

Citation Information

Bower, S.M., McGladdery, S.E., Price, I.M. (1994): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Sirolpidium zoophthorum (Larval Mycosis) of Clams.

Date last revised: Fall 1994
Comments to Susan Bower

Date modified: