Distribution of haemic neoplasia of soft‐shelled clams in Prince Edward Island: an examination of anthropogenic factors and effects of experimental fungicide exposure

Abstract

Haemic neoplasia was first considered a disease of concern for soft-shell clams in Prince Edward Island (PEI) when it was diagnosed as the cause of mass mortalities in 1999. The aetiology of the disease remains elusive, but has been associated with environmental degradation. In this study, a 2-year (2001-2002) geographic and seasonal survey was conducted for haemic neoplasia, using histology, in soft-shell clams from PEI. In addition, using geographic information system, the association between anthropogenic factors in the watersheds at sites affected by haemic neoplasia and the prevalence of the disease was investigated. Finally, histopathological changes were assessed in soft-shell clams experimentally exposed to four concentrations of chlorothalonil for 27 days. Haemic neoplasia could not be induced at any concentration of chlorothalonil. Clams exposed to a concentration of 1000 μg L(-1) of the fungicide, however, exhibited an LC50 of 17 days. Although this information provides additional toxicity information (LC50) for soft-shell clams, further experiments are required to assess longer term exposure to the fungicide. The highest prevalences of haemic neoplasia in PEI were found in North River and Miscouche (28.3-50.9% and 33.0-77.8%, respectively). No clear seasonal patterns were found. There was a correlation between haemic neoplasia prevalence and watersheds with a high percentage of potato acreage and forest coverage (P = 0.026 and P = 0.045, respectively), suggesting a link between anthropogenic activity and the prevalence of the disease.

Field and laboratory transmission studies of haemic neoplasia in the soft‐shell clam, Mya arenaria, from Atlantic Canada

“…This disease has been documented in M. arenaria in the United States (Brown et al 1977;Yevich & Barszcz 1977;Reinisch, Charles & Stone 1984;Farley et al 1986a;Brousseau 1987;Leavitt et al 1990;Weinberg et al 1997) and in Atlantic Canada (McGladdery, Drinnan & Stephenson 1993;Morrison et al 1993;McGladdery et al 2001;MacCallum 2003;Delaporte et al 2008;Muttray et al 2012;Mateo et al 2015). Most cases of HN occur at low prevalences (< 5%) and are not associated with mortalities; however, some incidents of higher prevalence in the United States have been associated with mass mortalities in mussels (Elston et al 1992) and soft-shell clams (Farley et al 1986a,b;McLaughlin, Farley & Hetrick 1992).…”

“…; Mateo et al . ). Most cases of HN occur at low prevalences (< 5%) and are not associated with mortalities; however, some incidents of higher prevalence in the United States have been associated with mass mortalities in mussels (Elston et al .…”

“…For instance, in a 2001–2002 histopathologic survey, prevalences of up to 50.9% and 77.8% were found in North River and Miscouche, PEI, respectively (Mateo et al . ). In other surveys, 38% of soft‐shell clams from North River, PEI (Delaporte et al .…”

“…In addition, some PEI locations are known to have high prevalence and intensity of the disease. For instance, in a 2001-2002 histopathologic survey, prevalences of up to 50.9% and 77.8% were found in North River and Miscouche, PEI, respectively (Mateo et al 2015). In other surveys, 38% of soft-shell clams from North River, PEI (Delaporte et al 2008), and 11.1% of soft-shell clams from Glovers Shore, Wilmot River, PEI (Muttray et al 2012) were found to be heavily affected by HN, using flow cytometry and immunocytochemistry, respectively.…”