Triploid eastern oysters (Crassostrea virginica) display high susceptibility to microbial infections but only during early ontogenetic stages

Over the last two decades, oyster aquaculture has largely shifted from the use of diploids to the near-exclusive use of triploids in many regions, with some hatcheries now producing >90 % triploid oyster spat. The increased demand for triploids is primarily driven by substantial growth advantages and more consistent meat quality associated with sterile triploid animals, with most data suggesting triploids and diploids display comparable adult survivorship. Although adult performance appears similar, anecdotal reports from farmers have suggested that triploids may exhibit greater frailty during earlier age classes, particularly in response to bacterial infections. Due to the extent of triploid production now taking place, the possibility of early ontogenetic frailty in triploids could pose a significant risk to oyster aquaculture production. To evaluate these claims, two cohorts of half-sibling diploid and triploid eastern oyster lines were generated in 2020 and 2021. A subset of larvae and juveniles from these lines were then exposed to a cocktail of bacterial (Vibrio) pathogens and monitored for viability. The remaining oysters were then allowed to grow for another 2 months before being deployed in either Peconic Bay, New York (2020), or Patuxent River, Maryland (2021), where their survivorship was followed for another year. Results showed that triploids were at significantly greater risk of mortality during the larvae and juvenile stages, though differential mortality decreased with age. These trends were consistent across the two spawning events, and the extent of early ontogenetic triploid frailty was observed to vary between the lines tested. This work provides valuable data for hatchery managers and farmers alike and suggests areas where specific attention and further work are required.