Eastern oyster (Crassostrea virginica) aquaculture is expanding rapidly in the United States. Although, oyster aquaculture is extensively studied in other states, the benefits of floating gear and the performance of oysters is lacking in Georgia. We assessed the effect OysterGro™ cages had upon shell height, shell width, shell depth, survival, and condition of diploid and triploid oysters. Diploid and triploid oysters were deployed in floating cages from December 2018 – January 2020 at two sites; an exposed, high fetch site in Wassaw Sound (WS) and a protected, low fetch site in the Skidaway River (SR). Survival and growth were monitored quarterly over the research duration with condition index assessment at the conclusion of the study.
Findings of this research indicated that triploid oysters had (p<0.001) greater shell height (89.9 mm +0.6 SE) than diploid oysters (77.4 mm +0.6 SE). Shell height differed between sites (p<0.001) with oysters in SR larger (91.6 mm +0.7 SE) than oysters in WS (75.7 mm +0.5 SE). Survival differed between ploidy in the summer (p=0.003) and fall (p=0.006) with diploids having higher survival (93.1% and 98.1%) than triploids (84.1% and 93.6%). Site survival differed in summer (p=0.002) and fall (p=0.006) with WS higher (93.8% and 97.8%) than the SR (84.0% and 93.9%). We did observe a substantial drop on triploid oyster survival in late summer and early fall at SR which was not observed in triploids at WS or in diploid oysters (Figure 1). Oyster condition was highest in diploids.
This study provides first data comparing the growth and survival of diploid and triploid oysters in OysterGro™ system in coastal Georgia. Our results indicate that floating gear is a viable option to grow market-sized oysters for harvest, but that environmental factors at growing location and ploidy can significantly affect seasonal survival and growth of oysters.