Prevalence of Perkinsus spp. in Chesapeake Bay soft-shell clams, Mya arenaria linnaeus, 1758 during 1990-1998

Prevalence and intensity of Perkinsus spp. injections were determined in soft-shell clams Mya arenaria during 1990 to 1998 based upon incubation of rectal tissues in Ray's fluid thioglycollate medium. During the study, soft-shell clams were collected from 18 sites in the upper Chesapeake Bay in Maryland. Enlarged hypnospores were found in similar to 7% (114/1,705) of the soft-shell clams. Peak prevalences occurred in the fall of 1992 with similar to 53% (16/30) at Piney Point and 50% (15/30) at Eastern Neck, and in August 1995 with similar to 64% (18/28) and similar to 37% (11/30) at Cedar Point and Piney Point, respectively. This investigation provides evidence that Perkinsus spp. infections in soft-shell clams are more common than previously thought.