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Abstracts
Workgroup: Frontiers in Disease Research
Comparison of physiological condition and defense mechanisms among eastern oyster populations with "natural Dermo resistance"
Principal Investigator(s):
Fu-Lin E. Chu, Virginia Institute of Marine Science, School of Marine Science, College of William and Mary, Gloucester Point, VA, chu@vims.edu
Funding Period: October 1, 1999 to September 30, 2001.
The objectives of the project were to compare the disease resistance in putative "natural Dermo resistant (NDR) and non-resistant" populations deployed in Chesapeake Bay and determine whether Dermo tolerance/resistance is a result of enhanced growth characteristics or specific defense parameters. To achieve these objectives, stocks representative of putative NDR and disease susceptible populations were selected and spawned. The progenies from these stocks were deployed and raised in two Dermo-enzootic sites of the Chesapeake Bay from September 1999 to December 2001. These stocks included: two NDR from Chesapeake Bay (Rappahannock River, CRB; Tangier Sound, CTS), two NDR from Gulf of Mexico, Louisiana (Grande Terre, LGT; Oyster Bayou, LOB), one susceptible control from Chesapeake Bay (Choptank River, CCR) and Louisiana (Hackberry Bay, LHB), and a positive control hatchery resistant strain (CROSBreed, XB, 9 generation for MSX, 4 generation for Dermo). Over the two-year study, oysters were sampled monthly or bimonthly from deployed stocks to determine Dermo infection, mortality, growth, cellular and humoral defense-related activities (plasma protease inhibition activity, plasma lysozyme activity, number of circulation hemocytes, ability of hemocytes to kill P. marinus) and physiological condition (condition index, tissue protein, lipid and glycogen content). Variation in growth and survival occurred among these natural stocks. The CRB stock grew fastest, reaching market size (3") within 18 months, but had the highest Dermo prevalence and intensity and lowest survival at both deployed sites (average ~10% at two sites). Generally, Chesapeake stocks had higher levels of Dermo infection than Louisiana stocks. Despite higher Dermo intensity than Louisiana stocks and similar to CRB, CTS consistently had lower mortality in both deployed sites. The CTS stock's disease tolerance (MSX and Dermo) and growth performance is comparable to the hatchery disease resistant strain, XB, with slightly better survivorship (~60%) than XB (50%). The LOB stock had a survivorship of 50% when exposed to Dermo alone and grew to the largest size over all stocks (3.5-4.0"). However, although Louisiana stocks had lower Dermo infection, results from the second year suggest that the LOB stock was less tolerant to cold climate and more susceptible to MSX. These results provide evidence that natural disease resistance does exist. Condition index varied seasonally and was related to variation in glycogen content. These parameters were similar among stocks and did not correlate strongly with degree of infection. The measured cellular and humoral defense-related parameters did not show any correlation among individuals within a oyster stock and between oyster stocks, and with Dermo infection and mortality over time.
IMPACTS and/or BENEFITS:
Via the funding of this project, we identified a natural disease resistant Chesapeake Bay stock (Tangier sound, CTS) which showed comparable disease tolerance and growth performance to the hatchery disease resistant strain (XB). Results of our study further demonstrated that Louisiana stocks are Dermo tolerant. Based on our findings, the VIMS Aquaculture Genetics and Breeding Technology Center (ABC) crossed Louisiana oysters with the XB hatchery strain in 2001, to increase resistance to Dermo and MSX, which will significantly benefit the burgeoning aquaculture industry in the Chesapeake Bay. Presently, Middle Peninsula Aquaculture sells oyster seed produced by Tangier Sound brood stock and Chesapeake Bay Aquaculture is using Louisiana and Tangier Sound brood stock for commercial oyster production. Cooperation with Regent Point and Port Kinsale marinas have resulted in further research projects continuing at these sites. Finally, through a series of meetings, workshops, and collaborative seminars, we have disseminated information to members of non-commercial oyster gardener associations across Virginia, as well as the scientific community. Additionally, to disseminate results, numerous papers (a total of 7) had been presented at international and national conferences. Several manuscripts are currently in preparation and will be submitted for publication.
PROJECT PUBLICATIONS:
Encomio, V.G., S. Stickler, F.-L. E. Chu. 2002. Evaluation of physiological condition in Dermo resistant oysters. J. Shellfish Res. 21: 373.
Stickler, S., V. Encomio, S. K. Allen, and F.-L. E. Chu. "Natural Dermo resistance" in eastern oyster stocks: Chesapeake studies and defense-related activities. J. Shellfish Res. 21:376.
Stickler, S. M., V. G. Encomio, F.-L. E. Chu, and S. K. Allen. 2000. Growth, mortality, and defense against Perkinsus marinus in eastern oysters, Crassostrea virginica. J. Shellfish Res. 19:666-667.
Encomio, V. G., S. M. Stickler, and F.-L. E. Chu. Energy reserves in Perkinsus marinus infected and uninfected oysters. J. Shellfish Res. 19: 662.
Encomio, V., S. Stickler, F.-L. E. Chu and S. Allen (In preparation). Physiological condition and energy reserves associated with Dermo infection and mortality in natural Dermo tolerant/resistant and susceptible oyster stocks. J. Shellfish Res.
Stickler, S.M. V.G. Encomio, J.F. LaPeyre, S.K. Allen, Jr., F.-L. E. Chu. (In preparation). Defense-related activities associated with natural Dermo resistance. J.Shellfish Res.
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