|
|
|
Abstracts
Workgroup: Aquaculture and Hatchery Issues
The Caribbean Oyster: Genetic Resource for American Oyster Culture?
Principal Investigator(s):
John Scarpa, Harbor Branch Oceanographic Institution, Inc., Ft. Pierce, FL, jscarpa@hboi.edu
CO-INVESTIGATOR and AFFILIATION: David Bushek, Baruch Marine Field Lab., Georgetown, SC
CO-INVESTIGATOR and AFFILIATION: David Bushek, Baruch Marine Field Lab., Georgetown, SC
Funding Period: 10/01/99 - 09/30/01
The Caribbean oyster Crassostrea rhizophorae is a closely related species of C. virginica, but little is known of its susceptibility to Dermo. Therefore, pathogenicity of Dermo was compared between the two oyster species.
Objective 1. Isolate, verify, and maintain in culture the Perkinsus spp. present in the Caribbean oyster. This was attempted three times, but the objective was not met. Perkinsus assays were positive, but revealed low infection intensities that effectively eliminated our ability to successfully isolate the parasite.
Objective 2. Propagate Caribbean and American oysters and culture the progeny under conditions that maintain them Dermo-free. American and Caribbean oysters were conditioned and spawned at HBOI. Larvae and set oysters were reared under strict quarantine using 1-?m filtered, UV-irradiated seawater to prevent infection by P. marinus. After six to eight months, oysters had grown large enough (~50mm, some were sexually mature) for experimental use and none had become infected with Dermo, providing the first demonstration that these methods can be employed to produce SPF oysters in Florida where Perkinsus marinus is endemic.
Objective 3. Compare Dermo tolerance, or resistance, of Dermo-free Caribbean oysters to Dermo-free American oysters by challenging them with isolates of Perkinsus marinus. SPF oysters were inoculated with one of two genetically distinct isolates of P. marinus. One isolate was originally derived from Fort Pierce, FL oysters (ATCC 50762) and the other isolate was from Cotuit Bay, MA (ATCC 50783). Only fifteen American oysters and one Caribbean oyster died during the course of the 16-week experiment. However, whole-body burden infection intensities (log10 transformed) in surviving oysters were significantly heavier for Caribbean oysters (1.25 "0.08) compared to American oysters (0.72 "0.06). Control oysters did not develop infections (0.09"0.01).
Objective 4. Compare "natural" Dermo infection levels in Caribbean oysters to American oysters. In January 2001, SPF oysters were placed in an upland system receiving unfiltered seawater. Effluent was passed through a chlorination tank and UV-system to prevent release of gametes of the non-native Caribbean oysters into local waters. A second control group of SPF American oysters was placed in the channel that provided the source of water for the tanks. Growth and survival of this second control group of oysters were much better (1303% wt gain, 89% survival) than those held in the experimental tanks (56-130% wt gain, 0-27% survival), indicating that our experimental conditions were less than optimal. Nonetheless, comparisons between the experimental populations were valid and revealing because replicates of both species were maintained together in the tanks. In the tanks, American oysters grew faster than Caribbean oysters (130% vs 56%), but Caribbean oysters had higher rates of overall survival (10% vs 2%). After 103 days, only a few parasites were detectable in about 50% of the oysters of either species. After 214 days, virtually all of the American oysters had died and prevalence of P. marinus was 100% in survivors; 24% of which had moderate to heavy infections (>1000 parasites/g wet meat weight). Most Caribbean oysters had died as well, although survival was better and 10% remained free of Perkinsus. Only 13% of surviving Caribbean oysters had moderate to heavy infections.
The results indicate that Caribbean oysters have the same or slightly less resistance to North American isolates of Perkinsus as compared to American oysters, but may be more tolerant of heavier parasite loads because mortality was higher in American oysters. The higher survival levels and tolerance to higher parasite burdens of the Caribbean oyster compared to the American oyster indicate that there is a genetic component needing further study, but efforts to use C. rhizophorae as a genetic resource for directly improving resistance of C. virginica to P. marinus are unlikely to yield productive results. Further comparisons may prove valuable in the elucidation of mechanisms of parasite invasion, parasite virulence, and host resistance.
IMPACTS and/or BENEFITS:
Our demonstration that Dermo-free oysters can be produced in Florida, where Perkinsus is widespread, is very significant. First, it demonstrates that it is not necessary to rear oysters in waters where the parasite is not known to occur to obtain Dermo-free oysters. More importantly, the ability to produce and rear SPF oysters in Florida with only slight modifications to existing hatchery technology has tremendous implications for the shellfish industry. Presently, several states have regulations against importing clams or oysters from hatcheries in Florida unless they are certified to be free of Perkinsus. For out of state customers, Florida hatcheries should be able to virtually guarantee a supply of Dermo-free seed using the methods demonstrated in this project.
PROJECT PUBLICATIONS:
Bushek, D., Scarpa, J. and Laramore, S.E. 2002. Susceptibility of the Caribbean oyster Crassostrea rhizophorae to Perkinsus marinus. J. Shellfish Res., 21: 371-372 (abstract from Nat. Shellfish. Assoc. 94th Conference, Mystic, CT, 14-18 April 2002).
Scarpa, J., Bushek, D. and Laramore, S.E. (presentation) Comparative pathogenicity of Dermo (Perkinsus marinus) between the Caribbean and American oyster. Int'l. Symp. Aquatic Animal Health, New Orleans, LA, 1-5 September 2002.
Scarpa, J., Laramore, S.E. and Bushek, D. (presentation) Comparative resistance between Caribbean Crassostrea rhizophorae and American C. virginica oysters to Dermo disease Perkinsus marinus. Aquaculture America 2002, San Diego, CA, 27-30 January 2002.
![[Maryland Sea Grant]](../mdsg_logo.gif){kind=logo}
![[NOAA]](../noaa_logo.gif){kind=logo}
![[Virginia Sea Grant]](../vasg_logo.gif){kind=logo}