Date Awarded


Document Type


Degree Name

Master of Science (M.Sc.)


Virginia Institute of Marine Science


Standish K. Allen

Committee Member

Roger L. Mann

Committee Member

Jeffrey D. Shields

Committee Member

Jessica Moss Small


Rapid growth rate and partial sterility have made triploid eastern oysters (Crassostrea virginica) the most popular crop variety for the Virginia oyster aquaculture industry, typically comprising greater than 90% of larvae and juvenile sales. Triploid advantages, however, sometimes come with the disadvantage of higher mortality in late spring and early summer, dubbed “triploid mortality.” In recent years, farms up and down the East Coast, especially Maryland and south into the Gulf of Mexico have experienced triploid mortality. Some of the reports include observations of elevated triploid fecundity. Triploid oysters are created by crossing tetraploids to diploids, and much of the commercial broodstock is acquired through the Virginia Institute of Marine Science Aquaculture Genetics and Breeding Technology Center (ABC). Tetraploid oysters are created from fecund triploid females and propagated favoring the most fertile tetraploids. We hypothesized that heritable fertility may be transferred to the commercial product, possibly yielding fertile triploid oysters. To investigate this possibility, twelve half-sibling families were produced by crossing individual tetraploid males with aliquots from a pooled source of eggs from diploid females. Tetraploid males came from tetraploid lines bred for one, two, five, or eight generations. Two replicates of each family were deployed to two sites: a site known for episodes of triploid mortality on the Eastern Shore of Chesapeake Bay, and at a control site in the Rappahannock River. Temperature and salinity exhibited typical patterns at both sites while oysters were raised to market size. When compared to the control site, cumulative mortality of triploid oysters at the Eastern Shore location was significantly higher, with significantly lower growth rate and fecundity; the latter measured by direct egg counts at peak ripeness. Diploid oysters performed similarly at both sites and exhibited significantly greater fecundity than triploids. Fecundity differed significantly among several triploid families based upon paternal lineage, but fecundity did not vary as a function of tetraploid lineage.



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