The relationship between reproduction and mortality in triploid Crassostrea virginica: a matter of economic importance

The goal of this project is to maximize survival for commercially produced triploid Crassostrea virginica oysters in Virginia. Over the last few years, commercial oyster growers in Virginia have reported significant mortality events of triploid oysters during the spring and summer months. The summer of 2014 was the worst yet, as growers across the state reported summer mortality, most severe on the Eastern shore and in some cases as high as 85% of the crop (Karen Hudson, personal communication). Surviving oysters from some of these mortality events were sent to the Virginia Institute of Marine Science and several of the triploid oysters examined had significant gonadal development, an unexpected finding considering previous experience with triploid C. virginica suggests they are typically sterile. Genetics may be an explanation for the unusually high reproductive effort and mortality rate, as further investigation revealed much of the seed grown in Virginia is produced by crossing Virginia tetraploids with Maine diploids. The specific objectives are to determine variability in gametogenesis of triploids owing to crosses from different geographic origins and to establish the relationship between this variation and mortality. In February of 2015, two tetraploid broodstocks from Virginia (V) and Louisiana (L) origins were crossed with two diploid brood stocks of Virginia (V) and Maine (M) origin to create four triploid constructs (VVV, VVM, LLV, LLM). Diploid VV, VM, MV, and MM constructs were produced as controls. Seed was deployed to three commercial sites on the Eastern Shore that have experienced severe triploid mortality, as well as to a site on the Rappahannock River and a site on the York River. Oysters will be sampled monthly during the spring and summer months of 2016. Sampling will consist of monitoring growth and survival, as well as assessing the condition, gametogenic characteristics, and reproductive effort of triploids and diploids from each culture at each commercial site. Histology will be the primary tool for assessing the gametogenic characteristics and reproductive effort of sampled oysters