Comparing Responses of Triploid and Diploid Eastern Oysters, Crassostrea virginica, to Common Farm Stressors

Abstract

Commercial off-bottom aquaculture of the Eastern oyster, Crassostrea virginica, is challenged by repeated spring and summer mortality events that disproportionally affect triploid oysters. Many farmers believe common farm practices, especially during hot summer months, may cause triploids to die. This study aimed to investigate how diploid and triploid oysters react differently to common stressors imposed by farmers such as tumbling during size grading and desiccation to prevent bio-fouling. A field experiment was run to subject diploids and triploid oysters to these stressors and monitor their responses. Additionally, lab experiments were performed to assess the responses of diploid and triploid oysters to desiccation stress using shell-closing strength. Triploid oysters did not suffer from higher mortality rates than diploid oysters exposed to the same stress treatment in the field. Furthermore, triploids oysters were less vulnerable to repeated desiccation stress than diploid oysters during the lab trials. This study did not capture the environmental conditions that caused higher mortality in triploids, but it does rule-out two common farm practices as a likely cause. Hence, other factors, potentially environmental stress or the interaction of environmental factors and farm practices may limit triploid survival and warrant further study.

Key words: oysters, triploids, mortality, stress, aquaculture, shell-closing strength, SCS