Latent stress response in translocated eastern oysters (Crassostrea virginica) in the Gulf of St. Lawrence

Movement of animals between habitats, whether natural or human-driven, can expose them to environmental stressors that impact their physiology and survival. In aquaculture, understanding these stress responses is critical to improving production practices. The cultivation of eastern oysters (Crassostrea virginica (Gmelin, 1791)) in Atlantic Canada depends largely on stock transfers from natural collection sites to grow-out sites. However, significant mortality has been reported in the year following translocation. We investigated stress factors associated with oyster transfers from New Brunswick to the Magdalen Islands. Mortality was assessed in relation to transport conditions and physiological indicators (gaping behavior, condition index, and energy reserves). We found no direct effect of transport conditions on post-transfer mortality. However, oysters transported in June without temperature control experienced ~ 50% winter mortality and consistently low glycogen levels (< 27 mg.g-1 dry tissue), suggesting a link between low energy reserves and latent mortality. Condition index showed a decline in oyster health over time in this group. Behavioural assessments demonstrated comparable gaping activity across all groups immediately after transfer, reinforcing the hypothesis that transport-induced stress manifests as a delayed response rather than immediate mortality. These results emphasise the importance of the oysters' physiological state during transfer for their survival in the Gulf of St. Lawrence. Maintaining glycogen reserves above 27 mg.g-1 and a condition index above 5 may be crucial for overwintering success.