safeguarding our sydney rock oyster industry against qx disease
BUDGET EXPENDITURE: $200,000
PRINCIPLE INVESTIGATOR: Dr Cheryl Jenkins
ORGANISATION: NSW Department of Primary Industries
PROJECT CODE: 2022-191
PROJECT STATUS: Current
WHY IS THIS RESEARCH BEING UNDERTAKEN?
Outbreaks of QX disease in Port Stephens in 2022 and 2023 mark the continued spread of this disease into
Sydney rock oyster (SRO)-producing estuaries in NSW and QLD. In severe years, QX can cause up to 90% mortalities in affected stock, therefore this disease poses a major threat to an industry that is of substantial economic, historic and cultural value.
Despite the apparent presence of the causative agent (M. sydneyi) in nearly all estuaries undertaking SRO
production, disease only occurs in some, and biosecurity protocols further complicate SRO farming as stocks
from high-risk estuaries cannot be moved into estuaries that have a lower QX disease risk profile.
Reasons behind the expression of QX disease in some estuaries but not others currently remain unknown. In
France, a related parasite, M. refringens, was originally thought to be a widespread cause of marteiliosis in
the European flat oyster (Ostrea edulis) as well as mussels belonging to the genus Mytilus. M. refringens O
(oyster) type and M (mussel) type, which were originally described due their differential pathogenicities in the
respective hosts, have more recently been found to constitute separate species, with M type being renamed
as Marteilia pararefringens. A similar situation may exist in Australia with M. sydneyi constituting more than
one species and with the more pathogenic strains being responsible for QX disease outbreaks. Historically
these questions could not be meaningfully answered due a lack of genetic information about M. sydneyi;
however NSW DPI has recently undertaken a genome sequencing project on M. sydneyi that can facilitate
strain comparison. Therefore, one aim of this project is to characterise Marteilia strains from estuaries where
disease occurs, and compare with those from estuaries where disease does not occur, to better inform
biosecurity policies. If the M. sydneyi strains are identical across estuaries, then this may enable biosecurity
policy to be modified to allow oyster translocations across so called “high” and “low” risk estuaries. However,
if strains do differ across high and low risk estuaries, then any biosecurity policy will be aimed at protecting
estuaries not currently experiencing QX outbreaks from the introduction of high pathogenicity strains.
QX disease remains as the primary known threat for SRO production. Due to significant knowledge gaps in
how this disease is transmitted, the use of selectively bred QX resistant oysters is the main management tool
used to enable cultivation to continue in estuaries where the disease is enzootic. Increasing genetic gains for QX survival has been the primary objective of the breeding program since its inception. A genomics project (FRDC project 2021-122) is currently underway which aims to identify genetic markers for QX disease resistance to increase genetic progress for this trait. Batches of Richmond River Rock oyster (RRRO) produced by NSW DPI have shown high levels of of QX disease survival. Prior studies on RRROs suggest that genetically they are classified as SROs but they appear to have developed significant resistance, presumably due to years of exposure to QX in the Richmond River estuary where the disease in enzootic.
Preliminary experimental evidence suggests that RRROs display enhanced survival when exposed to QX
disease, justifying their inclusion in the selective breeding program. Therefore, the second aim of this project
is to assess QX survival of current RRRO families across multiple years of QX exposure and compare these
results to other QX-resistant families in the breeding program. This information will be used in this project to
formulate a breeding plan to create additional families using batches of RRROs that have been assessed for
QX survival.
OBJECTIVES:
-
To use previously generated genomic data from M. sydneyi to develop a multilocus sequence typing
scheme for Marteilia strains from SRO's. -
To screen samples collected from low-risk estuaries for M. sydneyi using qPCR.
-
To compare Marteilia MLST profiles of qPCR positive samples from low-risk estuaries with those from
M. sydneyi MLST profiles from high-risk estuaries. -
To create 10 additional families (in addition to the families produced for the 2023 year class breeding
run) that have a parent sourced from the Richmond River. -
To assess the QX survival of the 10 additional 2023 year class families as spat, adults and over two
seasons at multiple sites. -
To generate QX spat survival estimated breeding values (EBVs) for families with RRRO parents
produced for the YC2022 and 2023 year classes. -
To collect performance data (QX survival and growth) that allows comparison of RRROs and
commercial families from the Sydney Rock Oyster breeding program over two consecutive seasons of
QX disease.
RESOURCES GENERATED:
