Identification of stress biomarkers for optimizing heat defouling in farmed Eastern oysters (Crassostrea virginica)

Abstract

Biofouling is a major challenge in off-bottom oyster aquaculture, increasing labor costs and negatively impacting oyster growth and quality. Precision heat defouling, a method commonly used in Asia and Europe, is an effective alternative to traditional air-exposure methods used in North America. However, the physiological effects of short-term, high temperature heat immersion treatment on Eastern oysters (Crassostrea virginica) remains poorly understood. This study examined temporal changes in targeted enzymes following a single 15 s heat immersion at 60 °C to identify temporal changes in physiological biomarkers of thermal stress. Adult oyster tissues were sampled immediately (0 h) or 0.5, 2, 8, 24, 72, and 144 h following a immersion protocol. Internal temperature was recorded in a subset of oysters to provide context for thermal exposure during immersion. Catalase (CAT) and pyruvate kinase (PK) activity were measured from extracted mantle tissue and fast- and slow-twitch adductor muscle. CAT and PK activity showed significant tissue-specific and temporal responses. In both fast- and slow-twitch adductor muscles, CAT activity increased significantly over time, peaking at 0.5 h in fast-twitch muscle and 2 h in slow-twitch muscle. In contrast, adductor muscle PK activity was highest immediately after immersion protocol, then declined at timepoints. No significant temporal changes were observed in mantle tissue for either enzyme. These results suggest that CAT and PK are useful biomarkers for assessing thermal stress in Eastern oysters, particularly in the adductor muscle. Future work will build on these findings by examining several temperature-duration combinations and oyster size classes to establish precision heat-defouling parameters that minimize oyster stress while effectively reducing biofouling.