Triploid Oysters In The Chesapeake Bay: Comparison Of Diploid And Triploid Crassostrea Virginica

Diploid and triploid Eastern oysters, Crassostrea virginica, were tested at 3 sites characterized by low on moderate salinity regimes in the Virginia part of the Chesapeake Bay from November 2005 through October 2007. Both diploid and triploid cultures were replicated 3 times by producing separate spawns from different broodstock. Ploidy had a generally consistent effect on the performance of C. virginica at the 3 test sites. At the end of the study, in October 2007, and across all sites, triploid oysters had lower cumulative mortality than diploids (-34%), and greater shell height (+25%), whole weight (+88%), and yield (+152%), as well as a higher proportion of market-size oysters (+114%) than diploids. Both diploids and triploids were similarly infected by Perkinsus marinas and, to a lesser extent, by Haplosporidium nelsoni. In a closer look, growth parameters (shell height growth, whole weight, yield, and percentage of marketable oysters) were always higher in triploids than in diploids regardless of the parental source, strongly supporting the superior advantage of triploids. Similar results were obtained for cumulative mortality, but to a lesser extent as a result of the large variation in mortality for both diploid and triploid cohorts among sites, as well as a significant site-by-cohort interaction. Our report is the first clear illustration of variation for the cumulative mortality exhibited among different spawns in triploids, and comes with the lesson that care must be taken in experiments in which the goal is to test the effect of ploidy on this trait. Our results support the notion that selective breeding programs to reduce mortality, coupled with triploid production to increase growth, can further optimize yield. The best-performing replicate spawn had 80% survival after 2.5 y, and reached an average shell height of 92 mm, weighing 142 g

Performance of selectively-bred lines of eastern oyster, Crassostrea virginica, across eastern US estuaries

Eastern oyster, Crassostrea virginica, aquaculture has expanded greatly in recent years, but further growth of the industry is constrained by disease-related losses. Oyster breeding programs supporting the oyster aquaculture industry along the east coast of the US have targeted resistance to three prominent diseases: MSX, Dermo, and ROD, caused by Haplosporidium nelsoni, Perkinsus marinus, and Roseovarius crassostreae respectively. Consequently, selected oyster lines possess some level of resistance and/or tolerance but the extent to which these lines, derived from various programs, perform across diverse growing environments used by industry has not been tested. The performance of six selected eastern oyster lines was evaluated at five sites along the east coast of the US (Maine to Virginia) to 1) identify differences in performance among lines at each site, and 2) identify lines that perform well across all sites. Performance measures included growth, mortality, and yield over a 15-month evaluation period. During unusually high mortality events, subsets of oysters were processed for disease diagnosis. Growth trajectories were similar among lines within a site, but varied significantly across sites (78% of random variance explained). Oysters grown in Rhode Island were largest while oysters grown in Maine were smallest at the end of the study. Mortality varied greatly among lines at each site as well as among sites. Line × site interaction explained 61% of the total random variance in the mortality data. In Maine, extensive mortality was observed early in the year for all lines, coincident with increased ROD prevalence. In New Jersey and Virginia, unusually high mortality was evident in the UMFS, Clinton, and NEH-RI lines during the final months of the experiment when the prevalence of both Dermo and MSX were 100% and \u3c. 50%, respectively. NEH, DEBY, and hANA lines were less affected, demonstrating that lines selected to perform better in their native site surpassed those selected outside the area. Despite large and significant line × site interaction effects for mortality and yield, NEH, DEBY, and hANA performance was above average across all sites. These findings have important implications for oyster breeding strategies and industry practices