Document Type



Virginia Institute of Marine Science

Publication Date



Journal Of Shellfish Research





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The pathogen Perkinsus marinus (Dermo) was discovered in Chesapeake Bay in 1950. It was already widely distributed in the Bay and caused annual mortality below the mouth of the Rappahannock River. Annual mortality in trayed oysters at the Virginia Institute of Marine Science (VIMS) varied annually from 24% to 57% at this most favorable site for the disease. Over 2 million bushels of seed oysters from the James River public beds were transplanted annually to private beds in 4 major growing areas. These were Hampton Roads, lower Bay proper, Mobjack Bay at mouth of York River, and the Rappahannock River. The introduction of Haplosporidium nelsoni (MSX) in 1959 resulted in killing most oysters throughout the Bay, and private planting was abandoned. Extreme dry weather during the decade of the 1980s allowed both diseases to spread widely throughout the Bay, and the oysters became scarce everywhere. MSX retreated to its endemic area below the mouth of the Rappahannock River when salinities returned to average levels. Dermo destroyed oysters in the seed area of the James River, and it has persisted there tenaciously with low mortality. Market-oyster production dropped from 2 to 3 million bushels annually during the 1950s to 6,000 in 1993. No seed oysters are available, and planting of private beds has ceased. Recovery is slow, and the oyster industry in Virginia was destroyed.


History; Diseases; Chesapeake Bay; Pathogen; Mortality; Distribution; Oyster Culture

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