To determine if natural populations of the eastern oyster possess resistance to Perkinsus marinus, progeny representing several oyster stocks from the Chesapeake Bay and the Gulf of Mexico were deployed at two sites within the Chesapeake Bay. Mortality, P. marinus infection (prevalence and intensity), shell height, condition index, and energy reserves (glycogen, protein, and lipid) were compared between these stocks. Oyster stocks from the Chesapeake Bay had higher intensities of Dermo infection than Louisiana stocks, with differences among individual stocks. Throughout the 2-y study, a natural Dermo-resistant stock from Tangier Sound (CTS), was identified. Despite infection intensities approaching those of a susceptible Rappahannock River stock (CRB) and higher than a Gulf of Mexico stock (LOB), CTS consistently had lower mortality for the 2-y grow out, and was comparable to a hatchery disease-resistant strain (XB). At a site (Port Kinsale) where the significant parasite was P. marinus, the LOB stock grew to the largest shell heights and had significantly lower intensities of infection. However, the performance of the LOB stock was comparatively poorer at the other deployment site (Regent Point) where MSX was present. Shell heights were highest overall in the CRB stock at Regent Point, despite high susceptibility to disease. Condition index varied between stocks, although not necessarily along trends of disease resistance since condition was highest in the CRB and XB stocks. Variations in energy reserves were strongly influenced by season, but not disease, or stock origin. The present study shows that differences between stocks contain an underlying genetic component. Differences seen between deployed stocks in mortality, growth, and condition have strong implications for development of selective criteria for an aquaculture-based industry.
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Vol. 24 • No. 1