Available at: https://digitalcommons.calpoly.edu/theses/3398
Date of Award
8-2026
Degree Name
MS in Biological Sciences
Department/Program
Biological Sciences
College
College of Science and Mathematics
Advisor
Kristin Hardy & Kevin Johnson
Advisor Department
Biological Sciences
Advisor College
College of Science and Mathematics
Abstract
Aquaculture of Pacific oysters on the US West Coast is routinely impacted by seasonal unexplained mortality events. To better understand these large-scale mortality events in oyster aquaculture, shellfish growers and scientists in California have partnered together to conduct comparative, multi-estuary farm trials of discrete Pacific oyster (Crassostrea gigas) lineages. In this thesis we investigate how the more recently imported Midori lineage performs compared to the historically used Miyagi lineage, as well as a Hybrid (Midori x Miyagi) lineage. As part of a 7-month long field study from April-November of 2024 in Morro Bay and Tomales Bay, California, we evaluated whether there were differences in survival, growth, and condition index (CI) between Midori, Miyagi, and Hybrid Pacific oysters. We further explored physiological differences in stress resilience and energy reserves of each lineage via total antioxidant capacity (tAOX) and glycogen content assays in gill and mantle tissues from the Morro Bay oysters collected across the field trial. Finally, in February 2024 all three lineages reared in Morro Bay were exposed to a fully factorial lab-based stress challenge of heat (32˚C) and anoxia stressors. In both field and lab trials, Miyagi oysters demonstrated superior performance; they had the highest growth rates (as shell length and whole weight) and lowest field and lab mortality. Interestingly, Midori oysters had higher CI and gill tAOX than Miyagi oysters, while Hybrid oysters performed intermediately to both lineages in nearly every index measured in this study. The exception to this pattern was tissue glycogen content, which was found to be higher and less variable than in the other two lineages. Ultimately, Miyagi oysters appear to be the most resilient lineage for combatting unexplained seasonal mortality in West Coast aquaculture operations, though further research is needed to determine if Midori oyster performance will improve with continued selective breeding.