Parasites, pests and diseases in Atlantic Canadian clams

A total of 1893 soft-shell clams (Mya arenaria), 1056 bar clams (Spisula solidissima) and 2212 quahaugs (hard-shell clams) (Mercenaria mercenaria and M. mercenaria var. notata) collected from Atlantic Canada were examined for parasites, pests and diseases. Mya arenaria revealed infections by: Rickettsia-like prokaryotic bacteria; digenean metacercariae and sporocysts, Sphenophyra-like ciliates, and an unidentified cestode as well as haemic and gonadal neoplasia. Polydora; Cliona; turbellarians; trichodinid ciliates and an encysted copepod were found associated with M. arenaria. Spisula solidissima were infected by Rickettsia-like bacteria and digenean metacercariae. Shell deformities in the form of green nodules, Polydora , and a cardiac oedema were found in the bar clams examined. Mercenaria mercenaria and M. mercenaria var. notata were infected by: Rickettsia-like organisms, digenean metacercariae; turbellarian flatworms; copepod pearls; peritrichous ciliates (Vorticella sp.) and Quahaug Parasite “Unknown” (“QPX”).;No infections were associated with overt pathology, however, two conditions were investigated to determine potential pathogenic significance: gonadal neoplasia in softshell clams and QPX in hard-shell clams. Gonadal neoplasia was detected for the first time in Atlantic Canadian populations of soft-shell clams. Archived soft-shell clam material collected from DFO from Passamaquody Bay, N.B. in 1989 and 1990 revealed gonadal neoplasia in monthly prevalences ranging between 3.4–30.8%. QPX was detected in both wild quahaug populations (prevalence range 3.3–20.0%) and hatchery broodstock quahaugs (3.3–47.0%).;In vitro culture of QPX in Minimum Essential Medium (MEM), from infected quahaug tissue and pallila fluid (prevalence range 60–100%), appeared to be more sensitive at detecting this parasite than routine histology (6.7–11.0%). Laboratory inoculation challenges using MEM cultured QPX into tissues and holding water were performed on adult (>35 mm shell length) and seed quahaugs (<20 mm shell length; M. mercenaria and M. mercenaria var. notata) using both histology and MEM tissue culture as detection methods. Only adult quahaugs with QPX injected into the mantle cavity and adductor muscle were infected with the parasite. Seed quahaugs and water inoculation challenges were negative. Tissue culture in MEM was more sensitive most likely because it was detecting superficial QPX or a morphologically similar, but distinct species.