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Canadian Aquaculture R&D Review 2017

Shellfish: Oysters

Investigating Polydora Outbreak in New Brunswick Off-Bottom Cultured Oysters

A better understanding of the increased intensity and prevalence of Polydora related to environmental conditions and their impact on oyster health would assist industry in developing management and mitigation strategies.

Known simply as a “mudworm” or “blisterworm”, Polydora websteri has the ability to bore into the shells of live and dead shellfish. Commonly found in intertidal and subtidal areas in Atlantic Canada, its presence among New Brunswick oyster populations has normally been minor and usually of low intensity with burrows containing little or no mud. However, there have been sporadic increases of infestation rates observed in off-bottom (or suspension) oyster growing sites in New Brunswick. Some reports have indicated that heavy infestations can result in low meat quality, abscesses, alteration of growth patterns, and weakened shells (increasing predator susceptibility). This unusual increase could ultimately lead to serious impacts on oyster populations and result in economic losses for the aquaculture industry. To help identify the current impact of Polydora on New Brunswick oyster growing areas, this project aims to: 1) document the presentation and level of the infestation of Polydora; 2) document the impact of Polydora on overall oyster health; and 3) document distribution and infestation level of Polydora in relation to environmental conditions.

Date: APR. 2014–MAR. 2017

Funded by: DFO–Aquaculture Collaborative Research and Development Program (DFO–ACRDP)

Co-Funded by: Huîtres Aquador Oysters Inc.

Project Lead: Daniel Bourque, Mary Stephenson (DFO)

Project Team: Daniel Bourque, Mary Stephenson, Janelle McLaughlin, Jeff Clements (DFO)

Collaborators: Serge Gaudet (Huîtres Aquador Oysters Inc.)



Crassostrea virginica shells with varying degrees of mud blister impact from Polydora websteri. (A) shells not impacted, (B) shells mildly impacted , and (C) shells severely impacted. Mud blisters are outlined in red. Photo: Jeffery Clements (DFO)

Assessment of Oyster Spat Collection Potential in Bouctouche Bay, New Brunswick

The oyster culture industry in New Brunswick depends on the oyster spat collected at four sites–Bouctouche Bay, Cocagne Bay, Caraquet Bay, and Miramichi Bay. In 2009, lower than average oyster spat collection rates were a source of concern for producers. To properly manage these fluctuations, an in-depth understanding of the various factors influencing collection rates and recruitment numbers within the system is needed.

This project studied the factors influencing oyster spat collection in Bouctouche Bay, New Brunswick by using modelling techniques to reproduce the oyster larval transport from spawning to recruitment for environmental conditions observed in situ (in the field) and assessing the relative contribution of the various larval sources (wild versus cultured stock). This modelling will also help researchers evaluate the possible repercussions of one (or more) spat evolution scenarios on the hydrodynamics (examining the erosion effects on the flow of water and nutrients) and overall spat collection potential within the bay.

The results from this experiment showed that the seed collection area is located in a retention zone of the bay where renewal by Northumberland Strait waters is slowest and indicated that water circulation within Bouctouche Bay is sensitive to meteorological forcing (wind and atmospheric pressure). A particle tracking module was coupled with the hydrodynamic model in order to investigate in more detail the transport of oyster larvae within Bouctouche Bay. Further analysis of the particle tracking results is underway to provide the relative contribution of each area of the bay, the effects of meteorological and river forcing on these contributions, and potential modifications to this pattern in the context of a scenario where a storm would result in breaching of the sand dune in front of the seed collection area.

DateMAY 2013–JUN. 2015

Funded by: DFO–Aquaculture Collaborative Research and Development Program (DFO–ACRDP)

Co-Funded by: Entreprise Baie Acadienne Inc.

Project Lead: Thomas Guyondet (DFO)

Project Team: Marie-Josée Maillet (DAAF); Serge Jolicoeur (U Moncton); Dominique Bérubé (New Brunswick Department of Energy and Resource Development)

Collaborators: Entreprise Baie Acadienne Inc.



Impacts of Aquaculture Operations on the Genetic Health of Natural Populations of the Eastern Oyster, Crassostrea virginica

This information will allow for both a better assessment of the genetic health of Crassostrea virginica populations in the Maritimes, and for the establishment of hatchery-based breeding programs.

Oyster farmers currently rely on wild-caught seed (also known as spat) to stock their aquaculture sites. The number and quality of seed, however, is highly variable from year-to-year and juvenile oysters must often be sold and transported from regions with a high seed set (abundance) to regions with a poor seed set. To address this issue, a commercial-scale hatchery in New Brunswick is currently being developed to provide adequate oyster seed to oyster farms within the Maritimes. The potential impact of hatchery-spawned oysters, as well as transplanted wild-caught spat, on the genetic integrity of neighbouring wild oyster beds greatly depends on the factors underlying the genetic structure of natural populations. Conversely, the health and vigour of cultured oysters depends on the quality of available spat, whether from wild-caught sources or hatchery production.

This project will examine genetic diversity between populations of the Eastern Oyster, identify functional diversity in terms of health indicators such as condition index, growth, survival, and reproduction, as well as evaluate the potential impacts of gene flow between wild and cultivated oyster populations. The goal of this project is to evaluate the genetic sequence of natural oyster populations through the creation of a high-density linkage map for the molecular markers associated with functional diversity in the Eastern Oyster.

Date: APR. 2013–JUN. 2017

Funded by: DFO–Aquaculture Collaborative Research and Development Program (DFO–ACRDP)

Co-Funded by: L’Étang Ruisseau Bar Ltd.

Project Lead: Mark LaFlamme (DFO)

Project Team: Jean-René Arseneau, Royce Steeves (DFO); Martin Mallet (L’Étang Ruisseau Bar Ltd.)

Collaborators: André Mallet (L’Étang Ruisseau Bar Ltd.)



Quantifying the Effect of Winter Siltation and Burial on Crassostrea virginica’s Health

In commercial shellfish aquaculture operations located within the Gulf of St. Lawrence estuaries, mesh bags containing cultivated Eastern Oysters (Crassostrea virginica) are lowered onto soft seabeds in the autumn and recovered in the spring. Occasional mortalities suggest that oysters are vulnerable to sedimentation and burial during winter.

This study explored the cause-effect relationship of winter siltation and burial on oyster health and productivity. It provides the first complete assessment of winter quiescence (extended period of valve closure) in oysters. Specifically, this project found the following results:

  • The autumnal burial of Eastern Oysters into the sediment disrupts their quiescent behaviour and leads to irreversible and potentially lethal consequences, occurring approximately five months following burial. The risk of winter death from burial is real, and, consequently, overwintering oysters in deeper channel waters (soft-bottom sediments) is not recommended.
  • Burial had no effect on the tissue concentration of lipids, proteins, and glycogen, nor did it impact the energy content index that was developed from these biochemical constituents. Oysters had their valves completely closed most of the time, operating anaerobically, regardless of whether they were buried in the sediment or lying on top of it.
  • Buried oysters were likely physiologically stressed during quiescence. Early “rescue” unburying of quiescent oysters did not improve survival rates; instead, unearthing provoked stress and accelerated the depletion of energy reserves, suspected to be the result of oysters burning energy to remove excess silt clogging their gills. Because resuspending mesh bags in early spring would have minimal mitigation effect on survival rates, avoiding soft bottoms altogether (to avoid burial) remains best for oyster health and survival.

Date: JUL. 2014–JUN. 2016

Funded by: DFO–Aquaculture Collaborative Research and Development Program (DFO– ACRDP)

Co-Funded by: L’Étang Ruisseau Bar Ltd.

Project Lead: Luc Comeau (DFO)

Project Team: Claire Carver (Carver Marine Consulting); Jeffrey Davidson (UPEI); Jean-Bruno Nadalini, Réjean Tremblay (UQAR)

Collaborators: André Mallet (L’Étang Ruisseau Bar Ltd.)



Oysters on the sea floor in an eelgrass bed. Photo: Luc Comeau (DFO)

Improving Physiological Health of Oysters by Selecting Seed for Stress Resilience

Access to a consistent supply of high quality and resilient seed stocks (i.e., those with the capacity to launch an immune response when faced with pathogens or withstand fluctuations in salinity and temperature associated with climate change) has been identified as a key constraint for the continued viability and expansion of the Eastern Oyster industry in Atlantic Canada. Selecting oysters that are more efficient (lower metabolic need, better feed conversion, and lower reproductive effort) and have increased resistance to deal with stressful events (lower stress response) will ultimately be healthier and thus have greater resilience to pathogens and environmental changes. This project identified genetic markers in the Eastern Oyster associated with metabolic and feed absorption efficiency (10 SNPs and 14 SNPs. respectively) and produced a first generation crop of oysters. In 2017, the progeny will be monitored (and genotyped) to verify if they display these particular traits.

This project is focused on generating efficient and resilient oysters to ensure that if faced with a pathogen or environmental stressor, they will have an increased capacity to launch an immune response.

Date: JAN. 2015–JUN. 2017

Funded by: DFO–Aquaculture Collaborative Research and Development Program (DFO–ACRDP)

Co-Funded by: L’Écloserie Acadienne Ltd.

Project Lead: Denise Méthé (DFO)

Project Team: Sarah Stewart-Clark, Stephanie Hall (Dalhousie U); Gillian Tobin-Huxley (DFO); Fraser Clark (Mount Allison U)

Collaborators: Maurice Daigle (L’Écloserie Acadienne Ltd.)



Gillian Huxley-Tobin (DFO) sieving oyster larvae produced from selected broodstock. Photo: Denise Méthé (DFO)

Oyster larvae ready to set. Photo: Denise Méthé (DFO)

Eastern Oyster, Crassostrea virginica, Response to Environmental, Physiological, and Mechanical Stressors

In New Brunswick, oyster mortalities appear to be closely related to environmental factors (e.g., temperature, salinity, etc.) and husbandry (rearing) practices. The physiological health of the animal can determine how well it adapts to, and recovers from, exposure to potential stressors. This study investigated the relationship between oyster health and environmental changes to identify critical periods of physiological stress.

In 2013, the physiological health of oysters (phagocytosis, hemocyte viability, oxidative stress, lysosomal destabilization, condition index, tubule atrophy) from two culture sites in Richibucto estuary (Aldouane River, Indian Island) were evaluated monthly (10 oysters/site). Additional samples were taken during periods of expected stress (i.e., pre- and post-spawning, air drying). Air drying is a technique used by oyster growers to control fouling on culture gear and oysters.

Hemocyte mortality (8.4%) and lysosomal destabilization (40%) remained slightly above that reported in literature (5% and 30%, respectively). Phagocytic activity was normal, hovering around 20% with greater fluctuations at the Indian Island site. Oxidative stress was most apparent during summer months (June-Sept), as expected. Likewise, tubule atrophy indices were 5X higher during winter months (December–April) compared to the growing season (May–November).

Condition index remained above 30%, except in July–August (25%), due to spawning event—as confirmed through histology. Likewise, tubule atrophy was noticeably higher in pre-spawned individuals, indicative of no feeding activity. Interestingly, the other biomarkers showed no stress response to spawning. Finally, air drying was identified as a stressful event for oysters, but based solely on lysosomal destabilization. Lysosomal destabilization remains a sensitive biomarker of stress response in oysters.

Field monitoring established seasonal baseline levels for a number of physiological biomarkers of stress for oysters.

Date: OCT. 2012–JUN. 2015

Funded by: DFO–Aquaculture Collaborative Research and Development Program (DFO–ACRDP)

Co-Funded by: La Maison BeauSoleil Inc.

Project Lead: Daniel Bourque (DFO)

Project Team: Denise Méthé, Janelle McLaughlin (DFO)

Collaborators: Amédée Savoie (La Maison BeauSoleil Inc.)



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