Document Type



Virginia Institute of Marine Science

Publication Date



Eleven years of monitoring MSX (Minchinia nelsoni) in lower Chesapeake Bay has revealed no important changes in virulence, mortality rates and epizootiology. The James River has declined in seed production by factors of 5 to 10 times. Oysters in the seed area are rarely infected by MSX, but they have remained highly susceptible when transplanted to areas of MSX prevalence.

Some 80 lots of progeny have been bred in the laboratory and tested in the field for resistance to MSX between 1964 and 1970. The most resistant progeny were reared from highly selected parents that survived several years of MSX activity. Progeny from unselected parents of stocks in the upper James and York rivers often matched those from selected parents with occasional conspicuous exceptions. More susceptible were oysters bred from Potomac River and upper Chesapeake Bay stocks and those bred outside areas where MSX is endemic. Wild spatfalls in MSX areas exhibit low mortalities from the disease regardless of origin and history of parent stocks. In Virginia, MSX may usually be thwarted by use of seed reared in prevalent areas but scarcity of such seed and other factors of predation and smothering have prevented use of ravaged beds _formerly planted with James River seed.


Oysters -- Virginia -- Immunology