MG-06-01-005
Broodstock management for the Bras d’Or Lakes oyster breeding program -
resistance to MSX
The American oyster (Crassostrea virginica) is an economically,
ecologically and culturally important species in Cape Breton, Nova Scotia,
but populations have been in decline due to over-fishing, degradation of
habitats and by the appearance of the MSX parasite (Haplosporidium nelsoni)
in the Bras d’Or Lakes (Pitupa’q) in 2002. Rejuvenation of depleted
private leases and public beds through seeding and cultivation programs
has been proposed as part of the solution by DFO, Eskasoni Fish and
Wildlife Commission (EFWC) and other stakeholders. Importation of oysters
from outside of the Bras d’Or Lakes is not permitted in order to protect
the native oysters from exposure to Malpeque Disease. Furthermore, there
is recent molecular evidence that the Bras d’Or Lakes oyster is a
population genetically discrete from oysters found in the Gulf of St.
Lawrence. Therefore, aquaculture and the commercial resource must rely
solely on resident populations for future culture and enhancement
activities.
Since the onset of the MSX oyster disease, several disease
management/studies and oyster enhancement initiatives have been
undertaken, including the ACRDP project: “Initiation of a Bras d’Or Lakes
oyster breeding program for resistance to MSX“. A selective breeding
program for disease resistance/tolerance is seen by the different
stakeholders (DFO, oyster growers, Mi’kmaq elders) as another long-term
strategy for the recovery of the Bras d’Or oyster. This R&D project was
performed in 2005/06 by UINR at EFWC’s research facility in Eskasoni and
initiated a rotational breeding plan with oysters from specific sites
within the Bras d’Or Lakes. Crosses were performed in the new oyster
hatchery and progenies tested both for pedigree and disease status
(Canadian Technical Report in prep.).
During the course of the project, it became evident that the surviving
oysters collected from MSX infected sites did not optimally condition,
even though water and food quantity and quality standards were met: their
gonads were only partially full and they did not naturally spawn during a
thermal shock in July 2005. Gametes had to be stripped and then
fertilisation was performed according to the experimental protocol.
Finally, larvae were raised and their performance was comparable to that
of larvae raised in standard North-American oyster hatcheries. The direct
and/or indirect effects of the MSX parasite on the gametogenesis and
spawning of the oyster are not clear but, overall, MSX infection impedes
on the abilities of an adult oyster to properly reproduce.
Temperature and salinity are two factors influencing the activity the
MSX parasite H. nelsoni (Haskin and Ford 1982, Ford 1985). Temperatures
below 5oC or above 20oC have been reported to control infection. Previous
research has shown that H. nelsoni is inactive or absent at low salinity
(10 ppt or lower) and low salinity immersions of oysters have been used as
a control measure in Delaware Bay and Chesapeake Bay. However,
gametogenesis is also retarded at salinities below 5 ppt.
The present research project proposes to precisely determine the
time-temperature-salinity combinations needed for appropriate
gametogenesis and spawning in MSX infected broodstock. This is critical to
(1) ensure the success on the on-going breeding program for resistance to
MSX initiated in Eskasoni for the Bras d’Or Lakes oysters, and (2) refine
timing and zoning of oyster management activities within the Lakes.
Ford, S.E. 1985. Effects of salinity on survival of the MSX parasite
Haplosporidium nelsoni (Haskin, Stauber and Mackin) in oysters. Journal of
Shellfish Research 5(2): 85-90.
Haskin, H.H. and S.E. Ford. 1982. Haplosporidium nelsoni (MSX) on
Delaware Bay seed oyster beds: a host-parasite relationship along a
salinity gradient. Journal of Invertebrate Pathology 40: 338-405.
Project Start Date: June 12, 2006
Project Completion Date: December 31, 2007
For further information please contact: DFO project leader: Bénédikte
Vercaemer (VercaemerB@mar.dfo-mpo.gc.ca)
or Regional ACRDP Coordinator: Denise Méthé (E-mail:
MetheD@dfo-mpo.gc.ca).
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