Two objectives of the Pacific oyster (Crassostrea gigas) industry on the U.S. West Coast are currently (i) resistance to OsHV-1, a deadly oyster virus that is currently present in Tomales Bay and San Diego Bay, and (ii) robust triploid oysters, which are more palatable due to their inability to develop mature gonads in the summer months . The Molluscan Broodstock Program (MBP) is a Pacific oyster breeding program that works with industry stakeholders to reach these objectives. In 2018, field and laboratory trials conducted on MBP broodstock families showed that between 50% to 70% of the between-family variation in OsHV-1 survival was heritable. After one generation of genetic selection, we estimate that OsHV-1 field survival in the MBP increased by 30% using survival data collected in a laboratory trial, although a field trial is still in progress.
Triploid oysters, which are derived by crossing diploids and tetraploids, have a tendency to be sensitive to environmental fluctuations on the West Coast, and thus experience greater mortalities than diploids. One hypothesis attributes this sensitivity to the small genetic base of tetraploid Pacific oysters used by hatcheries; therefore, developing new stocks of tetraploids would allow this hypothesis to be tested. We developed a new method of selecting tetraploid larvae after polyploidy induction from diploids . The method was tested on one-day-old Kumamoto oyster (C. sikamea) larvae. After selection, larvae were returned to the hatchery system for further growth. Larval size at day five did not significantly differ between diploid ( mean: 80 μm , sd: 11 μm) and tetraploid ( mean: 74 μm , sd: 14 μm ) larvae. This method holds promise as it skips the intermediary triploid stage toward tetraploid induction, its applicability to any shellfish species with a larval stage similar to Crassostrea spp., and its ability to sidestep use of hazardous chemicals in the isolation of polyploid oysters.