Evaluation of resistance to Dermo in eastern oyster strains tested in Chesapeake Bay

We investigated growth, Dermo disease, and survival for nine groups of oysters, Crassostrea virginica (Gmelin) cultivated in Chesapeake Bay (CB). Five regional strains (upper CB, North Carolina (NC), South Carolina (SC), Louisiana (LA) and LA triploids) and four additional hybrid strains (CB oystersmatedwithNC, SC, LA and Texas (TX) oysters) were held in £oating rafts at three locations representative of lower CB: ‘low’ salinity (3^14 g L ),‘moderate’salinity (5^20 g L ) and ‘high’ salinity (14^24 g L ). At each site, patterns of growth and incidence of infection with Perkinsusmarinus (Levine), the causative agent of Dermo disease, were similar. However, mortality trends were markedly di¡erent at each site; the CB strain being notable for accelerated mortality following infection with P. marinus. In addition, hybrids between CB and all four of the regional strains exhibited similar accelerated mortality in response to infection. Mortality was strongly correlated with infection only at the high salinity site implicating interaction of di¡erences in both oyster strain and virulence of Dermo between moderate and high salinity areas as factors in di¡erential mortality across sites.