The sea scallop Placopecten magellanicus (Gmelin, 1791) fishery is the most valuable wild scallop fishery in the world. Landings are primarily adductor muscles, which are ideally creamy white and firm. Recently, an increasing number of dark brown to gray, flaccid, and stringy meats have been caught in areas of Georges Bank and the mid-Atlantic, causing concern in industry and management. The mortality of gray-meat scallops was investigated, and an anesthetization procedure was developed allowing assessment of meat color in live scallops for laboratory experiments. The mortality rate of gray-meat scallops compared with white-meat scallops was tested. Gray-meat infection was swift and fatal; 26 of the original 28 gray-meat scallops died, whereas only 1 of 28 white-meat scallops died. The gray-meat condition was clearly associated with apicomplexan parasite infection intensity. Gray-meat scallops were identified visually, with image analysis computer software, and cell counts of apicomplexan nuclei. Secondary infections and stressors, including the effect of senescence, boring worm (Polydora sp.), and boring sponge (Cliona vastifica), were examined. Shells exhibiting high levels of boring sponge and worm damage had significantly higher incidence of gray-meat scallops. The prevalence of gray meats in a scallop population changes the shell height-meat weight relationship and the estimates of natural mortality and fishing effort used in stock assessments. Understanding the impacts of this disease and how to manage the fishery in its presence is important for the future of the fishery.