Abstract
The economically important marine bivalve mollusc, Mercenaria mercenaria, (commonly called a northern quahog or hard clam), has endured considerable mortalities caused by a thraustochytrid pathogen called Quahog Parasite X (QPX). Data on the percent prevalence of QPX infections were compiled from published reports along with our data to describe the epizootiology of QPX disease. QPX infections occurred in clams collected from both cultured beds and wild populations, but a higher percentage of QPX cases (76.5%) were from cultured clam beds. In addition, samples from cultured beds had a significantly higher prevalence (29.2 ± 27.2%) of QPX infections compared with samples from wild populations (9.6 ± 9.6%). The highest prevalence of QPX infections occurred in clams from samples with an intermediate size range (shell lengths 20-55 mm). QPX infections occurred in both male and female clams, but infection prevalence does not appear to be correlated with sex or sex ratios. The geographical range of QPX-related clam mortalities was Atlantic Canada to the Eastern Shore of Virginia, USA. Only marginally significant differences were detected between the prevalence of QPX at different locations. There were no latitudinal gradients in QPX prevalence or frequencies, suggesting local factors were important in determining its distribution. Although QPX infections occurred throughout the year, no seasonal trends in the prevalence or frequencies of QPX were discernable. This summary of information available on QPX disease highlights the need for more thorough data collection regarding factors believed to be associated with its presence and severity in hard clams.
Highlights
The commercially important bivalve, Mercenaria mercenaria, has suffered catastrophic mortalities from eastern Canada to coastal Virginia because of a pathogen called Quahog Parasite X (QPX; Whyte et al 1994, Smolowitz et al 1998, Ragone-Calvo et al 1998)
The sample containing the largest clams was positive for QPX, it is not known if the largest clam was positive for QPX
There was no significant difference in the mean sizes of clams from samples that tested positive or negative for QPX infections (t-test, P 1⁄4 0.197; 37 of the samples did not include data for size of clams tested)
Summary
The commercially important bivalve, Mercenaria mercenaria, (northern quahog or hard clam), has suffered catastrophic mortalities from eastern Canada to coastal Virginia because of a pathogen called Quahog Parasite X (QPX; Whyte et al 1994, Smolowitz et al 1998, Ragone-Calvo et al 1998). QPX is a small (4–120 mm), spherical protist, characterized as a thraustochytrid (Whyte et al 1994, Maas et al 1999, Ragan et al 2000, Stokes et al 2002). In culture (Kleinschuster et al 1998, Brothers et al 2000) and in tissue section (Smolowitz et al 1998), QPX occurs in three life stages: (1) thalli that develop into (2) sporangia that rupture to release (3) endospores (immature thalli). Cultures of QPX proliferated best at 24°C, with a pH 7–8 and a salinity of 28 ppt and greater (Brothers et al 2000). Thraustochytrids have been documented in coastal and oceanic
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
