TESTING MATERNAL CONTRIBUTIONS IN TRIPLOID EASTERN OYSTERS (CRASSOSTREA VIRGINICA): A FIELD EVALUATION IN COASTAL ALABAMA

Abstract

With the establishment of off-bottom aquaculture in the northern Gulf of Mexico, triploid oysters have become the mainstay of production due to their well-documented advantages; however, there have been observations in recent years that triploid oysters can suffer from sudden high mortality. This study aimed to investigate the effects of broodstock origin, size, and ploidy on performance of eastern oysters (Crassostrea virginica) in coastal Alabama. Six groups of oysters were spawned from wild broodstock collected from three areas with different salinity regime histories to produce half-sibling diploids and triploids: Calcasieu Lake, Sister Lake, and Vermillion Bay in Louisiana. To determine the effect of broodstock, cohorts were deployed at three different sites in Alabama with expected differences in salinity regimes: Grand Bay, Dauphin Island, and Mobile Bay. The effect of size on diploid and triploid performance was determined by a simultaneous field experiment at Grand Bay, AL. Growth and survival were determined by monthly data collection. Both broodstock and ploidy affected growth at all three sites; at Mobile Bay and Dauphin Island broodstock and ploidy had an interactive effect, while broodstock was the only significant effect on daily growth at the Grand Bay site. However, ploidy was the only factor that had a significant effect on mortality (with triploids suffering higher mortality of varying magnitude across sites). Growth rates of Sister Lake oysters were significantly affected by size, with small size oysters growing significantly faster than both medium and large sized oyster, however size and ploidy had an interactive effect on growth rate with triploid Calcasieu Lake oysters growing significantly faster than all other treatments. Triploids experienced higher cumulative mortality than diploids in both Sister Lake and Calcasieu Lake oysters. From April to May, size and ploidy had a significant effect on interval mortality in Sister Lake oysters, with triploid large sized oysters experiencing significantly higher interval mortality than all other experimental treatments. However, triploid Calcasieu Lake oysters had significantly higher interval mortality than diploids from April to May. Evaluating and understanding the effect of these factors on triploid performance could help alleviate industry concerns and equip commercial hatcheries with information to improve seed stocks for farmers in less-than-ideal grow-out environments.